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Dillinger H, Peereboom SM, Kozerke S. Beat phenomena of oscillating readouts. Magn Reson Med 2024; 91:1498-1511. [PMID: 38173292 DOI: 10.1002/mrm.29957] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2023] [Revised: 11/15/2023] [Accepted: 11/17/2023] [Indexed: 01/05/2024]
Abstract
PURPOSE To demonstrate slowly varying, erroneous magnetic field gradients for oscillating readouts due to the mechanically resonant behavior of gradient systems. METHODS Projections of a static phantom were acquired using a one-dimensional (1D) EPI sequence with varying EPI frequencies ranging from 1121 to 1580 Hz on clinical 3T systems (30 mT/m, 200 T/m/s). Phase due to static B0 inhomogeneities was eliminated by a complex division of two separate scans with different polarities of the EPI readout. The temporal evolution of phase was evaluated and related to the mechanical resonances of the gradient systems derived from the gradient modulation transfer function. Additionally, the impact of temporally varying mechanical resonance effects on EPI was evaluated using an echo-planar spectroscopic imaging sequence. RESULTS A beat phenomenon resulting in a slowly varying phase was observed. Its temporal frequency was given by the difference between the EPI frequency and the mechanical resonance frequency of the activated gradient axis. The maximum erroneous, oscillating phase during phase encoding was ±0.5 rad for an EPI frequency of 1281 Hz. Echo-planar spectroscopic imaging images showed the resulting time-dependent stretching/compression of the FOV. CONCLUSION Oscillating readouts such as those used in EPI can result in low-frequency, erroneous phase contributions, which are explained by the beat phenomenon. Therefore, EPI phase-correction approaches may need to include beat effects for accurate image reconstruction.
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Affiliation(s)
- Hannes Dillinger
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
| | - Sophie M Peereboom
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
| | - Sebastian Kozerke
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
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2
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Burkhardt BEU, Kellenberger CJ, Callaghan FM, Valsangiacomo Buechel ER, Geiger J. Flow evaluation software for four-dimensional flow MRI: a reliability and validation study. LA RADIOLOGIA MEDICA 2023; 128:1225-1235. [PMID: 37620674 PMCID: PMC10547653 DOI: 10.1007/s11547-023-01697-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/16/2023] [Accepted: 08/09/2023] [Indexed: 08/26/2023]
Abstract
PURPOSE Four-dimensional time-resolved phase-contrast cardiovascular magnetic resonance imaging (4D flow MRI) enables blood flow quantification in multiple vessels, which is crucial for patients with congenital heart disease (CHD). We investigated net flow volumes in the ascending aorta and pulmonary arteries by four different postprocessing software packages for 4D flow MRI in comparison with 2D cine phase-contrast measurements (2D PC). MATERIAL AND METHODS 4D flow and 2D PC datasets of 47 patients with biventricular CHD (median age 16, range 0.6-52 years) were acquired at 1.5 T. Net flow volumes in the ascending aorta, the main, right, and left pulmonary arteries were measured using four different postprocessing software applications and compared to offset-corrected 2D PC data. Reliability of 4D flow postprocessing software was assessed by Bland-Altman analysis and intraclass correlation coefficient (ICC). Linear regression of internal flow controls was calculated. Interobserver reproducibility was evaluated in 25 patients. RESULTS Correlation and agreement of flow volumes were very good for all software compared to 2D PC (ICC ≥ 0.94; bias ≤ 5%). Internal controls were excellent for 2D PC (r ≥ 0.95, p < 0.001) and 4D flow (r ≥ 0.94, p < 0.001) without significant difference of correlation coefficients between methods. Interobserver reliability was good for all vendors (ICC ≥ 0.94, agreement bias < 8%). CONCLUSION Haemodynamic information from 4D flow in the large thoracic arteries assessed by four commercially available postprocessing applications matches routinely performed 2D PC values. Therefore, we consider 4D flow MRI-derived data ready for clinical use in patients with CHD.
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Affiliation(s)
- Barbara Elisabeth Ursula Burkhardt
- Paediatric Cardiology, Pediatric Heart Center, Department of Surgery, University Children's Hospital Zürich, Steinwiesstrasse 75, 8032, Zurich, Switzerland.
- Children's Research Center, University Children's Hospital Zürich, Zurich, Switzerland.
| | - Christian Johannes Kellenberger
- Department of Diagnostic Imaging, University Children's Hospital Zürich, Zurich, Switzerland
- Children's Research Center, University Children's Hospital Zürich, Zurich, Switzerland
| | - Fraser Maurice Callaghan
- Department of Diagnostic Imaging, University Children's Hospital Zürich, Zurich, Switzerland
- Children's Research Center, University Children's Hospital Zürich, Zurich, Switzerland
| | - Emanuela Regina Valsangiacomo Buechel
- Paediatric Cardiology, Pediatric Heart Center, Department of Surgery, University Children's Hospital Zürich, Steinwiesstrasse 75, 8032, Zurich, Switzerland
- Children's Research Center, University Children's Hospital Zürich, Zurich, Switzerland
| | - Julia Geiger
- Department of Diagnostic Imaging, University Children's Hospital Zürich, Zurich, Switzerland
- Children's Research Center, University Children's Hospital Zürich, Zurich, Switzerland
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3
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Srinivas S, Masutani E, Norbash A, Hsiao A. Deep learning phase error correction for cerebrovascular 4D flow MRI. Sci Rep 2023; 13:9095. [PMID: 37277401 DOI: 10.1038/s41598-023-36061-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Accepted: 05/29/2023] [Indexed: 06/07/2023] Open
Abstract
Background phase errors in 4D Flow MRI may negatively impact blood flow quantification. In this study, we assessed their impact on cerebrovascular flow volume measurements, evaluated the benefit of manual image-based correction, and assessed the potential of a convolutional neural network (CNN), a form of deep learning, to directly infer the correction vector field. With IRB waiver of informed consent, we retrospectively identified 96 MRI exams from 48 patients who underwent cerebrovascular 4D Flow MRI from October 2015 to 2020. Flow measurements of the anterior, posterior, and venous circulation were performed to assess inflow-outflow error and the benefit of manual image-based phase error correction. A CNN was then trained to directly infer the phase-error correction field, without segmentation, from 4D Flow volumes to automate correction, reserving from 23 exams for testing. Statistical analyses included Spearman correlation, Bland-Altman, Wilcoxon-signed rank (WSR) and F-tests. Prior to correction, there was strong correlation between inflow and outflow (ρ = 0.833-0.947) measurements with the largest discrepancy in the venous circulation. Manual phase error correction improved inflow-outflow correlation (ρ = 0.945-0.981) and decreased variance (p < 0.001, F-test). Fully automated CNN correction was non-inferior to manual correction with no significant differences in correlation (ρ = 0.971 vs ρ = 0.982) or bias (p = 0.82, Wilcoxon-Signed Rank test) of inflow and outflow measurements. Residual background phase error can impair inflow-outflow consistency of cerebrovascular flow volume measurements. A CNN can be used to directly infer the phase-error vector field to fully automate phase error correction.
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Affiliation(s)
- Shanmukha Srinivas
- Department of Radiology, University of California San Diego, 200 West Arbor Drive, San Diego, CA, 92103, USA
- Department of Radiology, University of California Los Angeles, 757 Westwood Plaza, Los Angeles, CA, 90095, USA
| | - Evan Masutani
- Department of Radiology, University of California San Diego, 200 West Arbor Drive, San Diego, CA, 92103, USA
| | - Alexander Norbash
- Department of Radiology, University of California San Diego, 200 West Arbor Drive, San Diego, CA, 92103, USA
| | - Albert Hsiao
- Department of Radiology, University of California San Diego, 200 West Arbor Drive, San Diego, CA, 92103, USA.
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4
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Fischer C, Wetzl J, Schaeffter T, Giese D. Fully automated background phase correction using M-estimate SAmple consensus (MSAC)-Application to 2D and 4D flow. Magn Reson Med 2022; 88:2709-2717. [PMID: 35916368 DOI: 10.1002/mrm.29363] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2022] [Revised: 05/11/2022] [Accepted: 05/25/2022] [Indexed: 11/07/2022]
Abstract
PURPOSE Flow quantification by phase-contrast MRI is hampered by spatially varying background phase offsets. Correction performance by polynomial regression on stationary tissue may be affected by outliers such as wrap-around or constant flow. Therefore, we propose an alternative, M-estimate SAmple Consensus (MSAC) to reject outliers, and improve and fully automate background phase correction. METHODS The MSAC technique fits polynomials to randomly drawn small samples from the image. Over several trials, it aims to find the best consensus set of valid pixels by rejecting outliers to the fit and minimizing the residuals of the remaining pixels. The robustness of MSAC to its few parameters was investigated and verified using third-order polynomial correction fits on a total of 118 2D flow (97 with wrap-around) and 18 4D flow data sets (14 with wrap-around), acquired at 1.5 T and 3 T. Background phase was compared with standard stationary correction and phantom correction. Pulmonary/systemic flow ratios in 2D flow were derived, and exemplary 4D flow analysis was performed. RESULTS The MSAC technique is robust over a range of parameter choices, and a unique set of parameters is suitable for both 2D and 4D flow. In 2D flow, phase errors were significantly reduced by MSAC compared with stationary correction (p = 0.005), and stationary correction shows larger errors in pulmonary/systemic flow ratios compared with MSAC. In 4D flow, MSAC shows similar performance as stationary correction. CONCLUSIONS The MSAC method provides fully automated background phase correction to 2D and 4D flow data and shows improved robustness over stationary correction, especially with outliers present.
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Affiliation(s)
- Carola Fischer
- Department of Medical Imaging, Technical University of Berlin, Berlin, Germany.,Magnetic Resonance, Siemens Healthcare, Erlangen, Germany
| | - Jens Wetzl
- Magnetic Resonance, Siemens Healthcare, Erlangen, Germany
| | - Tobias Schaeffter
- Department of Medical Imaging, Technical University of Berlin, Berlin, Germany.,Biomedical Imaging, Physikalisch-Technische Bundesanstalt, Braunschweig and Berlin, Berlin, Germany.,School of Imaging Sciences and Biomedical Engineering, King's College London, London, UK
| | - Daniel Giese
- Magnetic Resonance, Siemens Healthcare, Erlangen, Germany.,Institute of Radiology, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), University Hospital Erlangen, Erlangen, Germany
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Gilbert KM, Dubovan PI, Gati JS, Menon RS, Baron CA. Integration of an RF coil and commercial field camera for ultrahigh-field MRI. Magn Reson Med 2021; 87:2551-2565. [PMID: 34932225 DOI: 10.1002/mrm.29130] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Revised: 11/16/2021] [Accepted: 12/03/2021] [Indexed: 11/08/2022]
Abstract
PURPOSE To develop an RF coil with an integrated commercial field camera for ultrahigh field (7T) neuroimaging. The RF coil would operate within a head-only gradient coil and be subject to the corresponding design constraints. The RF coil can thereafter be used for subject-specific correction of k-space trajectories-notably in gradient-sensitive sequences such as single-shot spiral imaging. METHODS The transmit and receive performance was evaluated before and after the integration of field probes, whereas field probes were evaluated when in an optimal configuration external to the coil and after their integration. Diffusion-weighted EPI and single-shot spiral acquisitions were employed to evaluate the efficacy of correcting higher order field perturbations and the consequent effect on image quality. RESULTS Field probes had a negligible effect on RF-coil performance, including the transmit efficiency, transmit uniformity, and mean SNR over the brain. Modest reductions in field-probe signal lifetimes were observed, caused primarily by nonidealities in the gradient and shim fields of the head-only gradient coil at the probe positions. The field-monitoring system could correct up to second-order field perturbations in single-shot spiral imaging. CONCLUSION The integrated RF coil and field camera was capable of concurrent-field monitoring within a 7T head-only scanner and facilitated the subsequent correction of k-space trajectories during spiral imaging.
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Affiliation(s)
- Kyle M Gilbert
- Centre for Functional and Metabolic Mapping, The University of Western Ontario, London, Ontario, Canada.,Department of Medical Biophysics, The University of Western Ontario, London, Ontario, Canada
| | - Paul I Dubovan
- Centre for Functional and Metabolic Mapping, The University of Western Ontario, London, Ontario, Canada.,Department of Medical Biophysics, The University of Western Ontario, London, Ontario, Canada
| | - Joseph S Gati
- Centre for Functional and Metabolic Mapping, The University of Western Ontario, London, Ontario, Canada.,Department of Medical Biophysics, The University of Western Ontario, London, Ontario, Canada
| | - Ravi S Menon
- Centre for Functional and Metabolic Mapping, The University of Western Ontario, London, Ontario, Canada.,Department of Medical Biophysics, The University of Western Ontario, London, Ontario, Canada
| | - Corey A Baron
- Centre for Functional and Metabolic Mapping, The University of Western Ontario, London, Ontario, Canada.,Department of Medical Biophysics, The University of Western Ontario, London, Ontario, Canada
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Yavuz Ilik S, Otani T, Yamada S, Watanabe Y, Wada S. A subject-specific assessment of measurement errors and their correction in cerebrospinal fluid velocity maps using 4D flow MRI. Magn Reson Med 2021; 87:2412-2423. [PMID: 34866235 DOI: 10.1002/mrm.29111] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2021] [Revised: 11/17/2021] [Accepted: 11/17/2021] [Indexed: 11/05/2022]
Abstract
PURPOSE Phase-contrast MRI (PC-MRI) of cerebrospinal fluid (CSF) velocity is used to evaluate the characteristics of intracranial diseases, such as normal-pressure hydrocephalus (NPH). Nevertheless, PC-MRI has several potential error sources, with eddy-current-based phase offset error being non-negligible in CSF measurement. In this study, we assess the measurement error of CSF velocity maps obtained using 4D flow MRI and evaluate correction methods. METHODS CSF velocity maps of 10 patients with NPH were acquired using 4D flow MRI (velocity-encoding = 5 cm/s). Distributed phase offset error was estimated for a whole 3D background field by polynomial fitting using robust regression analysis. This estimated phase offset error was then used to correct the CSF velocity maps. The estimated error profiles were compared with those obtained using an existing 2D correction approach involving local background information near the region of interest. RESULTS The residual standard error of the polynomial fitting against the phase offset error extracted from the measured velocities was within 0.2 cm/s. The spatial dependencies of the phase offset errors showed similar tendencies in all cases, but sufficient differences in these values were found to indicate requirement of velocity correction. Differences of the estimated errors among other correction approaches were in the order of 10-2 cm/s, and the estimated errors were in good agreement with those obtained using existing approaches. CONCLUSION Our method is capable of estimating the measurement error of CSF velocity maps obtained from 4D flow MRI and provides quantitatively reasonable characteristics for the main CSF profile in the cerebral aqueduct in patients with NPH.
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Affiliation(s)
- Selin Yavuz Ilik
- Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan
| | - Tomohiro Otani
- Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan
| | - Shigeki Yamada
- Department of Neurosurgery, Shiga University of Medical Science, Otsu, Shiga, Japan
| | - Yoshiyuki Watanabe
- Department of Radiology, Shiga University of Medical Science, Otsu, Shiga, Japan
| | - Shigeo Wada
- Department of Mechanical Science and Bioengineering, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan
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7
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Minderhoud SCS, van der Velde N, Wentzel JJ, van der Geest RJ, Attrach M, Wielopolski PA, Budde RPJ, Helbing WA, Roos-Hesselink JW, Hirsch A. The clinical impact of phase offset errors and different correction methods in cardiovascular magnetic resonance phase contrast imaging: a multi-scanner study. J Cardiovasc Magn Reson 2020; 22:68. [PMID: 32938483 PMCID: PMC7495876 DOI: 10.1186/s12968-020-00659-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2020] [Accepted: 08/06/2020] [Indexed: 01/04/2023] Open
Abstract
BACKGROUND Cardiovascular magnetic resonance (CMR) phase contrast (PC) flow measurements suffer from phase offset errors. Background subtraction based on stationary phantom measurements can most reliably be used to overcome this inaccuracy. Stationary tissue correction is an alternative and does not require additional phantom scanning. The aim of this study was 1) to compare measurements with and without stationary tissue correction to phantom corrected measurements on different GE Healthcare CMR scanners using different software packages and 2) to evaluate the clinical implications of these methods. METHODS CMR PC imaging of both the aortic and pulmonary artery flow was performed in patients on three different 1.5 T CMR scanners (GE Healthcare) using identical scan parameters. Uncorrected, first, second and third order stationary tissue corrected flow measurement were compared to phantom corrected flow measurements, our reference method, using Medis QFlow, Circle cvi42 and MASS software. The optimal (optimized) stationary tissue order was determined per scanner and software program. Velocity offsets, net flow, clinically significant difference (deviation > 10% net flow), and regurgitation severity were assessed. RESULTS Data from 175 patients (28 (17-38) years) were included, of which 84% had congenital heart disease. First, second and third order and optimized stationary tissue correction did not improve the velocity offsets and net flow measurements. Uncorrected measurements resulted in the least clinically significant differences in net flow compared to phantom corrected data. Optimized stationary tissue correction per scanner and software program resulted in net flow differences (> 10%) in 19% (MASS) and 30% (Circle cvi42) of all measurements compared to 18% (MASS) and 23% (Circle cvi42) with no correction. Compared to phantom correction, regurgitation reclassification was the least common using uncorrected data. One CMR scanner performed worse and significant net flow differences of > 10% were present both with and without stationary tissue correction in more than 30% of all measurements. CONCLUSION Phase offset errors had a significant impact on net flow quantification, regurgitation assessment and varied greatly between CMR scanners. Background phase correction using stationary tissue correction worsened accuracy compared to no correction on three GE Healthcare CMR scanners. Therefore, careful assessment of phase offset errors at each individual scanner is essential to determine whether routine use of phantom correction is necessary. TRIAL REGISTRATION Observational Study.
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Affiliation(s)
- Savine C. S. Minderhoud
- Department of Cardiology, Erasmus Medical Center, University Medical Center Rotterdam, P.O. Box 2040, Room Rg-419, Rotterdam, 3000 CA the Netherlands
- Department of Radiology and Nuclear Medicine, Erasmus Medical Center, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Nikki van der Velde
- Department of Cardiology, Erasmus Medical Center, University Medical Center Rotterdam, P.O. Box 2040, Room Rg-419, Rotterdam, 3000 CA the Netherlands
- Department of Radiology and Nuclear Medicine, Erasmus Medical Center, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Jolanda J. Wentzel
- Department of Cardiology, Erasmus Medical Center, University Medical Center Rotterdam, P.O. Box 2040, Room Rg-419, Rotterdam, 3000 CA the Netherlands
| | - Rob J. van der Geest
- Department of Radiology, Division of Image Processing, Leiden University Medical Center, Leiden, The Netherlands
| | - Mohammed Attrach
- Department of Radiology and Nuclear Medicine, Erasmus Medical Center, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Piotr A. Wielopolski
- Department of Radiology and Nuclear Medicine, Erasmus Medical Center, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Ricardo P. J. Budde
- Department of Cardiology, Erasmus Medical Center, University Medical Center Rotterdam, P.O. Box 2040, Room Rg-419, Rotterdam, 3000 CA the Netherlands
- Department of Radiology and Nuclear Medicine, Erasmus Medical Center, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Willem A. Helbing
- Department of Radiology and Nuclear Medicine, Erasmus Medical Center, University Medical Center Rotterdam, Rotterdam, The Netherlands
- Division of Pediatric Cardiology, Department of Pediatrics, Erasmus Medical Center, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Jolien W. Roos-Hesselink
- Department of Cardiology, Erasmus Medical Center, University Medical Center Rotterdam, P.O. Box 2040, Room Rg-419, Rotterdam, 3000 CA the Netherlands
| | - Alexander Hirsch
- Department of Cardiology, Erasmus Medical Center, University Medical Center Rotterdam, P.O. Box 2040, Room Rg-419, Rotterdam, 3000 CA the Netherlands
- Department of Radiology and Nuclear Medicine, Erasmus Medical Center, University Medical Center Rotterdam, Rotterdam, The Netherlands
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Fold-Over Oversampling Effects in the Measurements of Cerebral Cerebrospinal Fluid and Blood Flows with 2D Cine Phase-Contrast MRI. Diagnostics (Basel) 2020; 10:diagnostics10060387. [PMID: 32526946 PMCID: PMC7345509 DOI: 10.3390/diagnostics10060387] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2020] [Revised: 06/04/2020] [Accepted: 06/05/2020] [Indexed: 11/16/2022] Open
Abstract
This prospective study investigated the effects of fold-over oversampling on phase-offset background errors with 2D-Cine phase contrast (Cine-PC) magnetic resonance imaging (MRI). It was performed on brain MRI and compared to conventional Full-field of view FOV coverage and it was tested with two different velocity encoding (Venc) values. We chose Venc = 100 mm/s to encode cerebrospinal fluid (CSF) flows in the aqueduct and 600 mm/s to encode blood flow in the carotid artery. Cine-PC was carried out on 10 healthy adult volunteers followed simultaneously by an acquisition on static agar-gel phantom to measure the phase-offset background errors. Pixel-wise correction of both the CSF and the blood flows was calculated through 32 points of the cardiac-cycle. We compared the velocity-to-noise ratio, the section area, the absolute and the corrected velocity (peak; mean and minimum), the net flow, and the stroke volume before and after correction. We performed the statistical T-test to compare Full-FOV and fold-over and Bland–Altman plots to analyze their differences. Our results showed that following phase-offset error correction, the blood stroke-volume was significantly higher with Full-FOV compared to fold-over. We observed a significantly higher CSF mean velocity and net flow values in the fold-over option. Compared to Full-FOV, fold-over provides a significantly larger section area and significantly lower peak velocity-offset in the aqueduct. No significant difference between the two coverages was reported before and after phase-offset in blood flow measurements. In conclusion, fold-over oversampling can be chosen as an alternative to increase spatial resolution and accurate cerebral flow quantification in Cine-PC.
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Williamson NH, Komlosh ME, Benjamini D, Basser PJ. Limits to flow detection in phase contrast MRI. JOURNAL OF MAGNETIC RESONANCE OPEN 2020; 2-3:100004. [PMID: 33345200 PMCID: PMC7745993 DOI: 10.1016/j.jmro.2020.100004] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
Pulsed gradient spin echo (PGSE) complex signal behavior becomes dominated by attenuation rather than oscillation when displacements due to flow are similar or less than diffusive displacements. In this "slow-flow" regime, the optimal displacement encoding parameter q for phase contrast velocimetry depends on the diffusive length scale q s l o w = 1 / l D = 1 / 2 D Δ rather than the velocity encoding parameter v enc = π/(qΔ). The minimum detectable mean velocity using the difference between the phase at +q slow and -q slow is 〈 v m i n 〉 = 1 / SNR D / Δ . These theories are then validated and applied to MRI by performing PGSE echo planar imaging experiments on water flowing through a column with a bulk region and a beadpack region at controlled flow rates. Velocities as slow as 6 μm/s are detected with velocimetry. Theories, MRI experimental protocols, and validation on a controlled phantom help to bridge the gap between porous media NMR and pre-clinical phase contrast and diffusion MRI.
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Affiliation(s)
- Nathan H. Williamson
- National Institute of General Medical Sciences, National Institutes of Health, Bethesda, MD, USA
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
- Corresponding author: Nathan H. Williamson,
| | - Michal E. Komlosh
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
- The Center for Neuroscience and Regenerative Medicine, Uniformed Service University of the Health Sciences, Bethesda, MD, USA
| | - Dan Benjamini
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
- The Center for Neuroscience and Regenerative Medicine, Uniformed Service University of the Health Sciences, Bethesda, MD, USA
| | - Peter J. Basser
- Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
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Paul EA, Solana AB, Duong J, Shah AM, Lai WW, Tan ET, Hardy CJ, Chelliah A. Evaluation of self-calibrated non-linear phase-contrast correction in pediatric and congenital cardiovascular magnetic resonance imaging. Pediatr Radiol 2020; 50:656-663. [PMID: 32047987 DOI: 10.1007/s00247-020-04623-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/09/2019] [Revised: 11/10/2019] [Accepted: 01/21/2020] [Indexed: 11/25/2022]
Abstract
BACKGROUND The need for background error correction in phase-contrast flow analysis has historically posed a challenge in cardiac magnetic resonance (MR) imaging. While previous studies have shown that phantom correction improves flow measurements, it impedes scanner workflow. OBJECTIVE To evaluate the efficacy of self-calibrated non-linear phase-contrast correction on flows in pediatric and congenital cardiac MR compared to phantom correction as the standard. MATERIALS AND METHODS We retrospectively identified children who had great-vessel phase-contrast and static phantom sequences acquired between January 2015 and June 2015. We applied a novel correction method to each phase-contrast sequence post hoc. Uncorrected, non-linear, and phantom-corrected flows were compared using intraclass correlation. We used paired t-tests to compare how closely non-linear and uncorrected flows approximated phantom-corrected flows. In children without intra- or extracardiac shunts or significant semilunar valvular regurgitation, we used paired t-tests to compare how closely the uncorrected pulmonary-to-systemic flow ratio (Qp:Qs) and non-linear Qp:Qs approximated phantom-corrected Qp:Qs. RESULTS We included 211 diagnostic-quality phase-contrast sequences (93 aorta, 74 main pulmonary artery [MPA], 21 left pulmonary artery [LPA], 23 right pulmonary artery [RPA]) from 108 children (median age 15 years, interquartile range 11-18 years). Intraclass correlation showed strong agreement between non-linear and phantom-corrected flow measurements but also between uncorrected and phantom-corrected flow measurements. Non-linear flow measurements did not more closely approximate phantom-corrected measurements than did uncorrected measurements for any vessel. In 39 children without significant shunting or regurgitation, mean non-linear Qp:Qs (1.07; 95% confidence interval [CI] = 1.01, 1.13) was no closer than mean uncorrected Qp:Qs (1.06; 95% CI = 1.00, 1.13) to mean phantom-corrected Qp:Qs (1.02; 95% CI = 0.98, 1.06). CONCLUSION Despite strong agreement between self-calibrated non-linear and phantom correction, cardiac flows and shunt calculations with non-linear correction were no closer to phantom-corrected measurements than those without background correction. However, phantom-corrected flows also demonstrated minimal differences from uncorrected flows. These findings suggest that in the current era, more accurate phase-contrast flow measurements might limit the need for background correction. Further investigation of the clinical impact and optimal methods of background correction in the pediatric and congenital cardiac population is needed.
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Affiliation(s)
- Erin A Paul
- Division of Pediatric Cardiology, Department of Pediatrics, New York-Presbyterian Morgan Stanley Children's Hospital, Columbia University Medical Center, 3959 Broadway, New York, NY, 10032, USA.
| | | | - Jimmy Duong
- Department of Biostatistics, Mailman School of Public Health, Columbia University Medical Center, New York, NY, USA
| | - Amee M Shah
- Division of Pediatric Cardiology, Department of Pediatrics, New York-Presbyterian Morgan Stanley Children's Hospital, Columbia University Medical Center, 3959 Broadway, New York, NY, 10032, USA
| | - Wyman W Lai
- Department of Pediatric Cardiology, Children's Hospital of Orange County, Orange, CA, USA
| | - Ek T Tan
- GE Global Research, Niskayuna, NY, USA
| | | | - Anjali Chelliah
- Division of Pediatric Cardiology, Department of Pediatrics, New York-Presbyterian Morgan Stanley Children's Hospital, Columbia University Medical Center, 3959 Broadway, New York, NY, 10032, USA
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Magdoom KN, Sarntinoranont M, Mareci TH. An MRI-based switched gradient impulse response characterization method with uniform eigenmode excitation. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 313:106720. [PMID: 32217424 PMCID: PMC7245110 DOI: 10.1016/j.jmr.2020.106720] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/06/2020] [Revised: 03/14/2020] [Accepted: 03/16/2020] [Indexed: 06/10/2023]
Abstract
Switching gradients generate eddy currents and mechanical vibrations of the gradient assembly causing errors in the gradient time integrals. This results in image distortions in k-space and inaccuracies in q-space imaging. The purpose of this work is to develop an MRI based unbiased measurement of the switched gradient impulse response function (sGIRF). A new gradient pattern, called the Tukey windowed Shifted Sine-Integral (Tw-SSI) pulse, is introduced to excite the gradient eigenmodes uniformly over a user-defined bandwidth. A 3D MRI-based method with Hadamard encoding was developed to map the spatiotemporal magnetic field generated after the excitation pulse to obtain the sGIRF for all the three gradient axes simultaneously. Compared to an energy-equivalent traditional trapezoidal pulse, the Tw-SSI pulse is able to excite the weak bandlimited cross-terms of the sGIRF by uniformly distributing the energy across eigenmodes. The developed field mapping method is sensitive enough to capture both the direct and cross-terms in the sGIRF. The various mechanical resonant modes of the gradient coils are also revealed, which were found to last longer than eddy currents in the shielded gradient coil studied. Tunable Tw-SSI pulse offers the flexibility to perform unbiased sGIRF measurements over a bandwidth of interest. Rapid MRI field mapping can be easily implemented in any MRI system. The method may be used to perform gradient pre-emphasis, to evaluate new gradient coil designs, and to characterize higher order shims.
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Affiliation(s)
- Kulam Najmudeen Magdoom
- Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, United States.
| | - Malisa Sarntinoranont
- Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, United States; J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL, United States
| | - Thomas H Mareci
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL, United States; Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL, United States
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Stationary tissue background correction increases the precision of clinical evaluation of intra-cardiac shunts by cardiovascular magnetic resonance. Sci Rep 2020; 10:5053. [PMID: 32193468 PMCID: PMC7081189 DOI: 10.1038/s41598-020-61812-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Accepted: 03/02/2020] [Indexed: 11/18/2022] Open
Abstract
We aimed to evaluate the clinical utility of stationary tissue background phase correction for affecting precision in the measurement of Qp/Qs by cardiovascular magnetic resonance (CMR). We enrolled consecutive patients (n = 91) referred for CMR at 1.5T without suspicion of cardiac shunt, and patients (n = 10) with verified cardiac shunts in this retrospective study. All patients underwent phase contrast flow quantification in the ascending aorta and pulmonary trunk. Flow was quantified using two semi-automatic software platforms (SyngoVia VA30, Vendor 1; Segment 2.0R4534, Vendor 2). Measurements were performed both uncorrected and corrected for linear (Vendor 1 and Vendor 2) or quadratic (Vendor 2) background phase. The proportion of patients outside the normal range of Qp/Qs was compared using the McNemar’s test. Compared to uncorrected measurements, there were fewer patients with a Qp/Qs outside the normal range following linear correction using Vendor 1 (10% vs 18%, p < 0.001), and Vendor 2 (10% vs 18%, p < 0.001), and following quadratic correction using Vendor 2 (7% vs 18%, p < 0.001). No patient with known shunt was reclassified as normal following stationary background correction. Therefore, we conclude that stationary tissue background correction reduces the number of patients with a Qp/Qs ratio outside the normal range in a consecutive clinical population, while simultaneously not reclassifying any patient with known cardiac shunts as having a normal Qp/Qs. Stationary tissue background correction may be used in clinical patients to increase diagnostic precision.
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Wilm BJ, Dietrich BE, Reber J, Vannesjo SJ, Pruessmann KP. Gradient Response Harvesting for Continuous System Characterization During MR Sequences. IEEE TRANSACTIONS ON MEDICAL IMAGING 2020; 39:806-815. [PMID: 31425067 DOI: 10.1109/tmi.2019.2936107] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
MRI gradient systems are required to generate magnetic field gradient waveforms with very high fidelity. This is commonly implemented by gradient system calibration and pre-emphasis. However, a number of mechanisms, particularly thermal changes, cause variation in the gradient response over time, which cannot be addressed by calibration approaches. To overcome this limitation, we present a novel method termed gradient response harvesting, where the gradient response is continuously characterized during the course of a normal MR sequence. Snippets of field measurements are repeatedly acquired during an MR sequence, and from these multiple field measurements and the known nominal MR sequence gradients, the gradient response and gradient/field offsets are calculated. The calculation is implemented in a model-based and a model-free variant. The method is demonstrated for EPI with high gradient duty-cycle, where the continuous gradient characterization is used to obtain k-space trajectory estimates that are employed in the subsequent image reconstruction. During the course of the MR sequence, changes in both the envelope and the phase of the gradient response functions were observed, including shifts of mechanical resonances. The gradient response changes were also reflected in the calculated uninterrupted gradient waveforms and thus in the k-space trajectories. Using the updated encoding information in the image reconstruction removed ghosting artifacts, that otherwise impaired the image quality. We introduced the concept of gradient response harvesting and demonstrated its feasibility. The obtained gradient response functions may be used for quality assurance/preventive maintenance, real-time adaptation of gradient pre-emphasis or to calculate uninterrupted gradient field evolutions.
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Callaghan FM, Burkhardt B, Geiger J, Valsangiacomo Buechel ER, Kellenberger CJ. Flow quantification dependency on background phase correction techniques in 4D‐flow MRI. Magn Reson Med 2019; 83:2264-2275. [DOI: 10.1002/mrm.28085] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2019] [Revised: 10/09/2019] [Accepted: 10/24/2019] [Indexed: 12/23/2022]
Affiliation(s)
- Fraser M. Callaghan
- Center for MR Research University Children's Hospital Zurich Switzerland
- Children's Research Center University Children's Hospital Zurich Switzerland
| | - Barbara Burkhardt
- Children's Research Center University Children's Hospital Zurich Switzerland
- Division of Pediatric Cardiology University Children's Hospital Zurich Switzerland
| | - Julia Geiger
- Children's Research Center University Children's Hospital Zurich Switzerland
- Department of Diagnostic Imaging University Children's Hospital Zurich Switzerland
| | - Emanuela R. Valsangiacomo Buechel
- Children's Research Center University Children's Hospital Zurich Switzerland
- Division of Pediatric Cardiology University Children's Hospital Zurich Switzerland
| | - Christian J. Kellenberger
- Children's Research Center University Children's Hospital Zurich Switzerland
- Department of Diagnostic Imaging University Children's Hospital Zurich Switzerland
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Sieren MM, Berlin C, Oechtering TH, Hunold P, Drömann D, Barkhausen J, Frydrychowicz A. Comparison of 4D Flow MRI to 2D Flow MRI in the pulmonary arteries in healthy volunteers and patients with pulmonary hypertension. PLoS One 2019; 14:e0224121. [PMID: 31648286 PMCID: PMC6812822 DOI: 10.1371/journal.pone.0224121] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2018] [Accepted: 10/06/2019] [Indexed: 01/23/2023] Open
Abstract
Purpose 4D and 2D phase-contrast MRI (2D Flow MRI, 4D Flow MRI, respectively) are increasingly being used to noninvasively assess pulmonary hypertension (PH). The goals of this study were i) to evaluate whether established quantitative parameters in 2D Flow MRI associated with pulmonary hypertension can be assessed using 4D Flow MRI; ii) to compare results from 4D Flow MRI on a digital broadband 3T MR system with data from clinically established MRI-techniques as well as conservation of mass analysis and phantom correction and iii) to elaborate on the added value of secondary flow patterns in detecting PH. Methods 11 patients with PH (4f, 63 ± 16y), 15 age-matched healthy volunteers (9f, 56 ± 11y), and 20 young healthy volunteers (13f, 23 ± 2y) were scanned on a 3T MR scanner (Philips Ingenia). Subjects were examined with a 4D Flow, a 2D Flow and a bSSFP sequence. For extrinsic comparison, quantitative parameters measured with 4D Flow MRI were compared to i) a static phantom, ii) 2D Flow acquisitions and iii) stroke volume derived from a bSSFP sequence. For intrinsic comparison conservation of mass-analysis was employed. Dedicated software was used to extract various flow, velocity, and anatomical parameters. Visualization of blood flow was performed to detect secondary flow patterns. Results Overall, there was good agreement between all techniques, 4D Flow results revealed a considerable spread. Data improved after phantom correction. Both 4D and 2D Flow MRI revealed concordant results to differentiate patients from healthy individuals, especially based on values derived from anatomical parameters. The visualization of a vortex, indicating the presence of PH was achieved in 9 /11 patients and 2/35 volunteers. Discussion This study confirms that quantitative parameters used for characterizing pulmonary hypertension can be gathered using 4D Flow MRI within clinically reasonable limits of agreement. Despite its unfavorable spatial and lesser temporal resolution and a non-neglible spread of results, the identification of diseased study participants was possible.
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Affiliation(s)
- Malte Maria Sieren
- Department of Radiology and Nuclear Medicine, University Hospital Schleswig-Holstein, Lübeck, Germany
- * E-mail:
| | - Clara Berlin
- Department of Radiology and Nuclear Medicine, University Hospital Schleswig-Holstein, Lübeck, Germany
| | - Thekla Helene Oechtering
- Department of Radiology and Nuclear Medicine, University Hospital Schleswig-Holstein, Lübeck, Germany
| | - Peter Hunold
- Department of Radiology and Nuclear Medicine, University Hospital Schleswig-Holstein, Lübeck, Germany
| | - Daniel Drömann
- Department of Pneumology, University Hospital Schleswig-Holstein, Lübeck, Germany
| | - Jörg Barkhausen
- Department of Radiology and Nuclear Medicine, University Hospital Schleswig-Holstein, Lübeck, Germany
| | - Alex Frydrychowicz
- Department of Radiology and Nuclear Medicine, University Hospital Schleswig-Holstein, Lübeck, Germany
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Hofman MBM, Rodenburg MJA, Markenroth Bloch K, Werner B, Westenberg JJM, Valsangiacomo Buechel ER, Nijveldt R, Spruijt OA, Kilner PJ, van Rossum AC, Gatehouse PD. In-vivo validation of interpolation-based phase offset correction in cardiovascular magnetic resonance flow quantification: a multi-vendor, multi-center study. J Cardiovasc Magn Reson 2019; 21:30. [PMID: 31104632 PMCID: PMC6526620 DOI: 10.1186/s12968-019-0538-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2018] [Accepted: 04/03/2019] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND A velocity offset error in phase contrast cardiovascular magnetic resonance (CMR) imaging is a known problem in clinical assessment of flow volumes in vessels around the heart. Earlier studies have shown that this offset error is clinically relevant over different systems, and cannot be removed by protocol optimization. Correction methods using phantom measurements are time consuming, and assume reproducibility of the offsets which is not the case for all systems. An alternative previously published solution is to correct the in-vivo data in post-processing, interpolating the velocity offset from stationary tissue within the field-of-view. This study aims to validate this interpolation-based offset correction in-vivo in a multi-vendor, multi-center setup. METHODS Data from six 1.5 T CMR systems were evaluated, with two systems from each of the three main vendors. At each system aortic and main pulmonary artery 2D flow studies were acquired during routine clinical or research examinations, with an additional phantom measurement using identical acquisition parameters. To verify the phantom acquisition, a region-of-interest (ROI) at stationary tissue in the thorax wall was placed and compared between in-vivo and phantom measurements. Interpolation-based offset correction was performed on the in-vivo data, after manually excluding regions of spatial wraparound. Correction performance of different spatial orders of interpolation planes was evaluated. RESULTS A total of 126 flow measurements in 82 subjects were included. At the thorax wall the agreement between in-vivo and phantom was - 0.2 ± 0.6 cm/s. Twenty-eight studies were excluded because of a difference at the thorax wall exceeding 0.6 cm/s from the phantom scan, leaving 98. Before correction, the offset at the vessel as assessed in the phantom was - 0.4 ± 1.5 cm/s, which resulted in a - 5 ± 16% error in cardiac output. The optimal order of the interpolation correction plane was 1st order, except for one system at which a 2nd order plane was required. Application of the interpolation-based correction revealed a remaining offset velocity of 0.1 ± 0.5 cm/s and 0 ± 5% error in cardiac output. CONCLUSIONS This study shows that interpolation-based offset correction reduces the offset with comparable efficacy as phantom measurement phase offset correction, without the time penalty imposed by phantom scans. TRIAL REGISTRATION The study was registered in The Netherlands National Trial Register (NTR) under TC 4865 . Registered 19 September 2014. Retrospectively registered.
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Affiliation(s)
- Mark B. M. Hofman
- Radiology and Nuclear Medicine, ICaR-VU, VU University Medical Center, PO Box 7057, 1007 MB Amsterdam, the Netherlands
| | - Manouk J. A. Rodenburg
- Radiology and Nuclear Medicine, ICaR-VU, VU University Medical Center, PO Box 7057, 1007 MB Amsterdam, the Netherlands
| | - Karin Markenroth Bloch
- Lund University Bioimaging Center, Lund University, SE-221 85 Lund, Sweden
- Philips Healthcare, SE-164 85 Stockholm, Sweden
| | - Beat Werner
- Department Diagnostic Imaging, University Children’s Hospital, Steinwiesstrasse 75, 8032 Zürich, Switzerland
| | - Jos J. M. Westenberg
- Radiology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, the Netherlands
| | | | - Robin Nijveldt
- Cardiology, ICaR-VU, VU University Medical Center, PO Box 7057, 1007 MB Amsterdam, the Netherlands
| | - Onno A. Spruijt
- Pulmonology, ICaR-VU, VU University Medical Center, PO Box 7057, 1007 MB Amsterdam, the Netherlands
| | - Philip J. Kilner
- Cardiovascular Magnetic Resonance Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP UK
| | - Albert C. van Rossum
- Cardiology, ICaR-VU, VU University Medical Center, PO Box 7057, 1007 MB Amsterdam, the Netherlands
| | - Peter D. Gatehouse
- Cardiovascular Magnetic Resonance Unit, Royal Brompton Hospital, Sydney Street, London, SW3 6NP UK
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Segmental differences of cervical spinal cord motion: advancing from confounders to a diagnostic tool. Sci Rep 2019; 9:7415. [PMID: 31092891 PMCID: PMC6520379 DOI: 10.1038/s41598-019-43908-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2019] [Accepted: 05/02/2019] [Indexed: 01/01/2023] Open
Abstract
Increased cranio-caudal spinal cord motion is associated with clinical impairment in degenerative cervical myelopathy. However, whether spinal cord motion holds potential as a neuroimaging biomarker requires further validation. Different confounders (i.e. subject characteristics, methodological problems such as phase drift, etc.) on spinal cord motion readouts have to be considered. Twenty-two healthy subjects underwent phase contrast MRI, a subset of subjects (N = 9) had repeated scans. Parameters of interest included amplitude of velocity signal, maximum cranial respectively maximum caudal velocity, displacement (=area under curve of the velocity signal). The cervical spinal cord showed pulse synchronic oscillatory motions with significant differences in all readouts across cervical segments, with a maximum at C5. The Inter-rater reliability was excellent for all readouts. The test-retest reliability was excellent for all parameters at C2 to C6, but not for maximum cranial velocity at C6 and all readouts at C7. Spinal cord motion was correlated with spinal canal size, heart rate and body size. This is the first study to propose a standardized MRI measurement of spinal cord motion for further clinical implementation based on satisfactory phase drift correction and excellent reliability. Understanding the influence of confounders (e.g. structural conditions of the spine) is essential for introducing cord motion into the diagnostic work up.
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Spinner GR, Stoeck CT, Mathez L, von Deuster C, Federau C, Kozerke S. On probing intravoxel incoherent motion in the heart‐spin‐echo versus stimulated‐echo DWI. Magn Reson Med 2019; 82:1150-1163. [DOI: 10.1002/mrm.27777] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2018] [Revised: 03/06/2019] [Accepted: 03/27/2019] [Indexed: 02/06/2023]
Affiliation(s)
- Georg R. Spinner
- Institute for Biomedical Engineering University and ETH Zurich Zurich Switzerland
| | - Christian T. Stoeck
- Institute for Biomedical Engineering University and ETH Zurich Zurich Switzerland
| | - Linda Mathez
- Institute for Biomedical Engineering University and ETH Zurich Zurich Switzerland
| | | | - Christian Federau
- Institute for Biomedical Engineering University and ETH Zurich Zurich Switzerland
| | - Sebastian Kozerke
- Institute for Biomedical Engineering University and ETH Zurich Zurich Switzerland
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Peters K, Weiss K, Maintz D, Giese D. Influence of respiration-induced B 0 variations in real-time phase-contrast echo planar imaging of the cervical cerebrospinal fluid. Magn Reson Med 2019; 82:647-657. [PMID: 30957288 DOI: 10.1002/mrm.27748] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Revised: 02/25/2019] [Accepted: 03/04/2019] [Indexed: 11/08/2022]
Abstract
PURPOSE Respiration induces temporal variations of the main magnetic field B0 along the spinal cord. These variations are typically not compensated for in velocity quantifications using phase-contrast MRI. The goal of this study was to analyze errors caused by respiration-induced B0 variations in real-time phase-contrast echo planar imaging (PCEPI) of cervical cerebrospinal fluid (CSF) velocity measurements and to evaluate this effect for various sequence parameters using numerical simulations. METHODS Real-time B0 measurements with double gradient echo sequence and PCEPI measurements were acquired in the cervical CSF of 10 healthy subjects. Dynamic phase offsets attributed to respiration-induced B0 variations were analyzed by quantifying amplitudes and comparing the temporal behavior with respiratory signals. In experiments and simulations, the influence of the echo time (TE) and the delay between PCEPI images (Δt) with respect to respiration on the dynamic phase offsets were investigated. RESULTS A good agreement was found between phase offsets extracted from both acquisition types. Furthermore, respiratory signals qualitatively matched the temporal behavior of the measured phase offsets showing a dependency on subject-dependent local B0 distribution and respiration physiology. Simulations revealed residual background phases in PCEPI velocity quantification varying with TE and Δt. CONCLUSION Respiration-induced B0 variations result in dynamic background phases in real-time PCEPI velocity quantifications of the CSF in the cervical spine. The current work underlines that these background phases need to be corrected to avoid confounding effects.
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Affiliation(s)
- Kristina Peters
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Institute for Diagnostic and Interventional Radiology, Cologne, Germany
| | - Kilian Weiss
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Institute for Diagnostic and Interventional Radiology, Cologne, Germany.,Philips GmbH, Hamburg, Germany
| | - David Maintz
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Institute for Diagnostic and Interventional Radiology, Cologne, Germany
| | - Daniel Giese
- University of Cologne, Faculty of Medicine and University Hospital Cologne, Institute for Diagnostic and Interventional Radiology, Cologne, Germany
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Magdoom KN, Zeinomar A, Lonser RR, Sarntinoranont M, Mareci TH. Phase contrast MRI of creeping flows using stimulated echo. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2019; 299:49-58. [PMID: 30579226 PMCID: PMC6402592 DOI: 10.1016/j.jmr.2018.12.009] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/10/2018] [Revised: 12/10/2018] [Accepted: 12/13/2018] [Indexed: 05/30/2023]
Abstract
Creeping flows govern many important physiological phenomena such as elevated interstitial fluid flows in tumors, glymphatic flows in the brain, among other applications. However, few methods exist to measure such slow flows non-invasively in optically opaque biological tissues in vivo. Phase-contrast MRI is a velocimetry technique routinely used in the clinic to measure fast flows in biological tissues, such as blood and cerebrospinal fluid (CSF), in the order of cm/s. Use of this technique to encode slower flows is hampered by diffusion weighting and phase error introduced by gradient hardware imperfections. In this study, a new PC-MRI technique is developed using stimulated echo preparation to overcome these challenges. Flows as slow as 1 μm/s are measured and validated using controlled water flow through a pipe at 4.7 T. The error in measured flow rate obtained by integrating the measured velocity over the cross-sectional area of the pipe is less than 10%. The developed method was also able to capture slow natural convection flows appearing in liquids placed inside a horizontal bore magnet. Monitoring the 4D velocity vector field revealed that the natural convection flows decay exponentially with time. This method could be applied in future to study creeping flows, e.g. in tissue.
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Affiliation(s)
- Kulam Najmudeen Magdoom
- Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, USA.
| | - Ahmad Zeinomar
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL, USA
| | - Russell R Lonser
- Department of Neurological Surgery, Wexner Medical Center, The Ohio State University, Columbus, OH, USA
| | - Malisa Sarntinoranont
- Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL, USA; J. Crayton Pruitt Family Department of Biomedical Engineering, 1275 Center Drive, Biomedical Sciences Building, Gainesville, FL, USA
| | - Thomas H Mareci
- Department of Biochemistry and Molecular Biology, University of Florida, Gainesville, FL, USA; J. Crayton Pruitt Family Department of Biomedical Engineering, 1275 Center Drive, Biomedical Sciences Building, Gainesville, FL, USA
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Kim M, Collier GJ, Wild JM, Chung YM. Effect of upper airway on tracheobronchial fluid dynamics. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2018; 34:e3112. [PMID: 29856119 DOI: 10.1002/cnm.3112] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 05/24/2018] [Accepted: 05/27/2018] [Indexed: 05/17/2023]
Abstract
The upper airways play a significant role in the tracheal flow dynamics. Despite many previous studies, however, the effect of the upper airways on the ventilation distribution in distal airways has remained a challenge. The aim of this study is to experimentally and computationally investigate the dynamic behaviour in the intratracheal flow induced by the upper respiratory tract and to assess its influence on the subsequent tributaries. Patient-specific images from 2 different modalities (magnetic resonance imaging of the upper airways and computed tomography of the lower airways) were segmented and combined. An experimental phantom of patient-specific airways (including the oral cavity, larynx, trachea, down to generations 6-8) was generated using 3D printing. The flow velocities in this phantom model were measured by the flow-sensitised phase contrast magnetic resonance imaging technique and compared with the computational fluid dynamics simulations. Both experimental and computational results show a good agreement in the time-averaged velocity fields as well as fluctuating velocity. The flows in the proximal trachea were complex and unsteady under both lower- and higher-flow rate conditions. Computational fluid dynamics simulations were also performed with an airways model without the upper airways. Although the flow near the carina remained unstable only when the inflow rate was high, the influence of the upper airways caused notable changes in distal flow distributions when the 2 airways models were compared with and without the upper airways. The results suggest that the influence of the upper airways should be included in the respiratory flow assessment as the upper airways extensively affect the flows in distal airways and consequent ventilation distribution in the lungs.
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Affiliation(s)
- Minsuok Kim
- School of Engineering, University of Warwick, Coventry, UK
| | - Guilhem J Collier
- Academic Unit of Radiology, Institute for In Silico Medicine, University of Sheffield, Sheffield, UK
| | - Jim M Wild
- Academic Unit of Radiology, Institute for In Silico Medicine, University of Sheffield, Sheffield, UK
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Magnetic Resonance Imaging technology-bridging the gap between noninvasive human imaging and optical microscopy. Curr Opin Neurobiol 2018; 50:250-260. [PMID: 29753942 DOI: 10.1016/j.conb.2018.04.026] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2017] [Revised: 04/20/2018] [Accepted: 04/24/2018] [Indexed: 12/23/2022]
Abstract
Technological advances in Magnetic Resonance Imaging (MRI) have provided substantial gains in the sensitivity and specificity of functional neuroimaging. Mounting evidence demonstrates that the hemodynamic changes utilized in functional MRI can be far more spatially and thus neuronally specific than previously believed. This has motivated a push toward novel, high-resolution MR imaging strategies that can match this biological resolution limit while recording from the entire human brain. Although sensitivity increases are a necessary component, new MR encoding technologies are required to convert improved sensitivity into higher resolution. These new sampling strategies improve image acquisition efficiency and enable increased image encoding in the time-frame needed to follow hemodynamic changes associated with brain activation.
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Ragunathan S, Pipe JG. Radiofrequency saturation induced bias in aqueductal cerebrospinal fluid flow quantification obtained using two-dimensional cine phase contrast magnetic resonance imaging. Magn Reson Med 2017; 79:2067-2076. [PMID: 28833454 DOI: 10.1002/mrm.26883] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2017] [Revised: 07/28/2017] [Accepted: 07/31/2017] [Indexed: 12/31/2022]
Abstract
PURPOSE To explore the extent of bias in cerebrospinal fluid flow estimates due to radiofrequency saturation, and its possible impact on the use of two-dimensional cine phase contrast magnetic resonance imaging in the diagnosis and characterization of normal pressure hydrocephalus in patients. THEORY AND METHODS Theoretical signal equations were generated to describe saturation dependence on velocity. An experimental set of phase contrast magnetic resonance imaging scans with two different flip angles was used to show bias in flow estimates in a flow phantom, and in six different healthy volunteers. The cerebral aqueduct was targeted as the flow region of interest. RESULTS Data from a constant flow phantom showed a spatial distribution of voxels with significant bias in flow at the periphery of the flow region. The velocity difference (bias) maps of the cerebral aqueduct correlated with the spatial velocity gradients around peak systole and peak diastole, and high correlation with temporal velocity gradients during transition between systole and diastole. The aqueductal stroke volume for θ = 30° were found to be significantly higher than for θ = 10° using a Wilcoxon signed rank test. CONCLUSION This work shows the extent of bias in cerebrospinal fluid flow quantification due to radiofrequency saturation effects. This clinical relevance of this error was presented with respect to shunt responsiveness among normal pressure hydrocephalus patients. Magn Reson Med 79:2067-2076, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
| | - James G Pipe
- Barrow Neurological Institute, Imaging Research, Phoenix, Arizona, USA
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Frydrychowicz A, Roldan-Alzate A, Winslow E, Consigny D, Campo CA, Motosugi U, Johnson KM, Wieben O, Reeder SB. Comparison of radial 4D Flow-MRI with perivascular ultrasound to quantify blood flow in the abdomen and introduction of a porcine model of pre-hepatic portal hypertension. Eur Radiol 2017; 27:5316-5324. [PMID: 28656461 DOI: 10.1007/s00330-017-4862-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2016] [Revised: 03/22/2017] [Accepted: 04/20/2017] [Indexed: 02/07/2023]
Abstract
OBJECTIVES Objectives of this study were to compare radial time-resolved phase contrast magnetic resonance imaging (4D Flow-MRI) with perivascular ultrasound (pvUS) and to explore a porcine model of acute pre-hepatic portal hypertension (PHTN). METHODS Abdominal 4D Flow-MRI and pvUS in portal and splenic vein, hepatic and both renal arteries were performed in 13 pigs of approximately 60 kg. In six pigs, measurements were repeated after partial portal vein (PV) ligature. Inter- and intra-reader comparisons and statistical analysis including Bland-Altman (BA) comparison, paired Student's t tests and linear regression were performed. RESULTS PvUS and 4D Flow-MRI measurements agreed well; flow before partial PV ligature was 322 ± 30 ml/min in pvUS and 297 ± 27 ml/min in MRI (p = 0.294), and average BA difference was 25 ml/min [-322; 372]. Inter- and intra-reader results differed very little, revealed excellent correlation (R 2 = 0.98 and 0.99, respectively) and resulted in BA differences of -5 ml/min [-161; 150] and -2 ml/min [-28; 25], respectively. After PV ligature, PV flow decreased from 356 ± 50 to 298 ± 61 ml/min (p = 0.02), and hepatic arterial flow increased from 277 ± 36 to 331 ± 65 ml/min (p = n.s.). CONCLUSION The successful in vivo comparison of radial 4D Flow-MRI to perivascular ultrasound revealed good agreement of abdominal blood flow although with considerable spread of results. A model of pre-hepatic PHTN was successfully introduced and acute responses monitored. KEY POINTS • Radial 4D Flow-MRI in the abdomen was successfully compared to perivascular ultrasound. • Inter- and intra-reader testing demonstrated excellent reproducibility of upper abdominal 4D Flow-MRI. • A porcine model of acute pre-hepatic portal hypertension was successfully introduced. • 4D Flow-MRI successfully monitored acute changes in a model of portal hypertension.
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Affiliation(s)
- A Frydrychowicz
- Department of Radiology, School of Medicine and Public Health, E3/366 Clinical Science Center, University of Wisconsin - Madison, 600 Highland Avenue, Madison, WI, 53792-3252, USA.
- Clinic for Radiology and Nuclear Medicine, University Hospital Schleswig-Holstein, Campus Lübeck, Ratzeburger Allee 160, 23562, Lübeck, Germany.
- University of Lübeck, Lübeck, Germany.
| | - A Roldan-Alzate
- Department of Radiology, School of Medicine and Public Health, E3/366 Clinical Science Center, University of Wisconsin - Madison, 600 Highland Avenue, Madison, WI, 53792-3252, USA
- Department of Mechanical Engineering, University of Wisconsin, Madison, USA
| | - E Winslow
- Department of Surgery, University of Wisconsin, Madison, USA
| | - D Consigny
- Department of Radiology, School of Medicine and Public Health, E3/366 Clinical Science Center, University of Wisconsin - Madison, 600 Highland Avenue, Madison, WI, 53792-3252, USA
| | - C A Campo
- Department of Radiology, School of Medicine and Public Health, E3/366 Clinical Science Center, University of Wisconsin - Madison, 600 Highland Avenue, Madison, WI, 53792-3252, USA
| | - U Motosugi
- Department of Radiology, School of Medicine and Public Health, E3/366 Clinical Science Center, University of Wisconsin - Madison, 600 Highland Avenue, Madison, WI, 53792-3252, USA
| | - K M Johnson
- Department of Medical Physics, University of Wisconsin, Madison, USA
| | - O Wieben
- Department of Radiology, School of Medicine and Public Health, E3/366 Clinical Science Center, University of Wisconsin - Madison, 600 Highland Avenue, Madison, WI, 53792-3252, USA
- Department of Medical Physics, University of Wisconsin, Madison, USA
| | - S B Reeder
- Department of Radiology, School of Medicine and Public Health, E3/366 Clinical Science Center, University of Wisconsin - Madison, 600 Highland Avenue, Madison, WI, 53792-3252, USA
- Department of Medical Physics, University of Wisconsin, Madison, USA
- Department of Biomedical Engineering, University of Wisconsin, Madison, USA
- Department of Medicine, University of Wisconsin, Madison, USA
- Department of Emergency Medicine, University of Wisconsin, Madison, USA
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25
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Oster J, Clifford GD. Acquisition of electrocardiogram signals during magnetic resonance imaging. Physiol Meas 2017; 38:R119-R142. [PMID: 28430109 DOI: 10.1088/1361-6579/aa6e8c] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The recording of the electrocardiogram (ECG) during magnetic resonance imaging (MRI) acquisition is of great interest and importance. Firstly, MRI acquisition is a relatively slow process, which therefore complicates the imaging of moving organs. Cardiac MRI requires the development of strategies for acquiring high quality images, which is mainly achieved by synchronising the image acquisition with a specific time during the cardiac cycle. The ECG is used to monitor the heart's activity, and the detection of the largest and steepest peak in the cardiac cycle (the QRS complex) triggers the acquisition of slices of the k-space. Secondly, patients undergoing an MRI examination need to be monitored for safety during the procedure, and therefore ECG signals are used to track their cardiovascular state in real time. However, there are significant barriers to the accurate observation and processing of the ECG during MRI acquisition. In particular, the flow of charged blood particles through the large applied magnetic field leads to an extra current source, known as the magnetohdrodymanic (MHD) effect. This review article discusses these barriers and state-of-the-art solutions. An overview of the relevant technology including hardware and applications are described. The development of new software tools for the processing of the ECG signals acquired during MRI is also detailed. These developments include the design of specific QRS detection algorithms, which are able to distinguish QRS complexes from the MHD effect but also the gradient artefacts. Different techniques for the suppression of the gradient artefacts are also presented as well as the most challenging problem to-date-the problem of separating the MHD effect from the ECG. The article concludes by summarising the advantages of using ECG signals during MRI, but also presents the current limitations of modern analysis techniques in this domain. The most promising avenues of research are also discussed and suggestions for new methodological analyses for the development of this field are given.
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Affiliation(s)
- Julien Oster
- IADI, U947, INSERM, Université de Lorraine, CHRU Nancy, Vandoeuvre-les-Nancy, France
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Busch J, Giese D, Kozerke S. Image-based background phase error correction in 4D flow MRI revisited. J Magn Reson Imaging 2017; 46:1516-1525. [PMID: 28225577 DOI: 10.1002/jmri.25668] [Citation(s) in RCA: 37] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Accepted: 01/26/2017] [Indexed: 11/07/2022] Open
Affiliation(s)
- Julia Busch
- Institute for Biomedical Engineering; University of Zurich and ETH Zurich; Zurich Switzerland
| | - Daniel Giese
- Department of Radiology; University Hospital Cologne; Cologne Germany
| | - Sebastian Kozerke
- Institute for Biomedical Engineering; University of Zurich and ETH Zurich; Zurich Switzerland
- Division of Imaging Science and Biomedical Engineering; King's College London; London UK
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27
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Heidari Pahlavian S, Bunck AC, Thyagaraj S, Giese D, Loth F, Hedderich DM, Kröger JR, Martin BA. Accuracy of 4D Flow Measurement of Cerebrospinal Fluid Dynamics in the Cervical Spine: An In Vitro Verification Against Numerical Simulation. Ann Biomed Eng 2016; 44:3202-3214. [PMID: 27043214 PMCID: PMC5050060 DOI: 10.1007/s10439-016-1602-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2016] [Accepted: 03/29/2016] [Indexed: 11/30/2022]
Abstract
Abnormal alterations in cerebrospinal fluid (CSF) flow are thought to play an important role in pathophysiology of various craniospinal disorders such as hydrocephalus and Chiari malformation. Three directional phase contrast MRI (4D Flow) has been proposed as one method for quantification of the CSF dynamics in healthy and disease states, but prior to further implementation of this technique, its accuracy in measuring CSF velocity magnitude and distribution must be evaluated. In this study, an MR-compatible experimental platform was developed based on an anatomically detailed 3D printed model of the cervical subarachnoid space and subject specific flow boundary conditions. Accuracy of 4D Flow measurements was assessed by comparison of CSF velocities obtained within the in vitro model with the numerically predicted velocities calculated from a spatially averaged computational fluid dynamics (CFD) model based on the same geometry and flow boundary conditions. Good agreement was observed between CFD and 4D Flow in terms of spatial distribution and peak magnitude of through-plane velocities with an average difference of 7.5 and 10.6% for peak systolic and diastolic velocities, respectively. Regression analysis showed lower accuracy of 4D Flow measurement at the timeframes corresponding to low CSF flow rate and poor correlation between CFD and 4D Flow in-plane velocities.
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Affiliation(s)
- Soroush Heidari Pahlavian
- Conquer Chiari Research Center, The University of Akron, Akron, OH, USA
- Department of Mechanical Engineering, The University of Akron, Akron, OH, USA
| | - Alexander C Bunck
- Department of Radiology, University Hospital of Cologne, Cologne, Germany
- Department of Radiology, University Hospital of Muenster, Muenster, Germany
| | - Suraj Thyagaraj
- Conquer Chiari Research Center, The University of Akron, Akron, OH, USA
- Department of Mechanical Engineering, The University of Akron, Akron, OH, USA
| | - Daniel Giese
- Department of Radiology, University Hospital of Cologne, Cologne, Germany
| | - Francis Loth
- Conquer Chiari Research Center, The University of Akron, Akron, OH, USA
- Department of Mechanical Engineering, The University of Akron, Akron, OH, USA
| | - Dennis M Hedderich
- Department of Radiology, University Hospital of Cologne, Cologne, Germany
| | - Jan Robert Kröger
- Department of Radiology, University Hospital of Muenster, Muenster, Germany
| | - Bryn A Martin
- Department of Biological Engineering, The University of Idaho, 875 Perimeter Drive MS 0904, Moscow, ID, 83844-0904, USA.
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Valvano G, Martini N, Huber A, Santelli C, Binter C, Chiappino D, Landini L, Kozerke S. Accelerating 4D flow MRI by exploiting low-rank matrix structure and hadamard sparsity. Magn Reson Med 2016; 78:1330-1341. [PMID: 27787911 DOI: 10.1002/mrm.26508] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2016] [Revised: 09/23/2016] [Accepted: 09/23/2016] [Indexed: 11/11/2022]
Affiliation(s)
- Giuseppe Valvano
- Department of Information Engineering; University of Pisa; Pisa Italy
- Fondazione G. Monasterio CNR-Regione Toscana; Massa Italy
| | - Nicola Martini
- Fondazione G. Monasterio CNR-Regione Toscana; Massa Italy
| | - Adrian Huber
- Institute for Biomedical Engineering; University and ETH Zurich; Zurich Switzerland
| | - Claudio Santelli
- Institute for Biomedical Engineering; University and ETH Zurich; Zurich Switzerland
| | - Christian Binter
- Institute for Biomedical Engineering; University and ETH Zurich; Zurich Switzerland
| | | | - Luigi Landini
- Department of Information Engineering; University of Pisa; Pisa Italy
- Fondazione G. Monasterio CNR-Regione Toscana; Massa Italy
| | - Sebastian Kozerke
- Institute for Biomedical Engineering; University and ETH Zurich; Zurich Switzerland
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Advanced flow MRI: emerging techniques and applications. Clin Radiol 2016; 71:779-95. [PMID: 26944696 DOI: 10.1016/j.crad.2016.01.011] [Citation(s) in RCA: 85] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2015] [Revised: 12/10/2015] [Accepted: 01/10/2016] [Indexed: 12/12/2022]
Abstract
Magnetic resonance imaging (MRI) techniques provide non-invasive and non-ionising methods for the highly accurate anatomical depiction of the heart and vessels throughout the cardiac cycle. In addition, the intrinsic sensitivity of MRI to motion offers the unique ability to acquire spatially registered blood flow simultaneously with the morphological data, within a single measurement. In clinical routine, flow MRI is typically accomplished using methods that resolve two spatial dimensions in individual planes and encode the time-resolved velocity in one principal direction, typically oriented perpendicular to the two-dimensional (2D) section. This review describes recently developed advanced MRI flow techniques, which allow for more comprehensive evaluation of blood flow characteristics, such as real-time flow imaging, 2D multiple-venc phase contrast MRI, four-dimensional (4D) flow MRI, quantification of complex haemodynamic properties, and highly accelerated flow imaging. Emerging techniques and novel applications are explored. In addition, applications of these new techniques for the improved evaluation of cardiovascular (aorta, pulmonary arteries, congenital heart disease, atrial fibrillation, coronary arteries) as well as cerebrovascular disease (intra-cranial arteries and veins) are presented.
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Phase Error Correction in Time-Averaged 3D Phase Contrast Magnetic Resonance Imaging of the Cerebral Vasculature. PLoS One 2016; 11:e0149930. [PMID: 26910600 PMCID: PMC4765993 DOI: 10.1371/journal.pone.0149930] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Accepted: 02/05/2016] [Indexed: 11/19/2022] Open
Abstract
Purpose Volume flow rate (VFR) measurements based on phase contrast (PC)-magnetic resonance (MR) imaging datasets have spatially varying bias due to eddy current induced phase errors. The purpose of this study was to assess the impact of phase errors in time averaged PC-MR imaging of the cerebral vasculature and explore the effects of three common correction schemes (local bias correction (LBC), local polynomial correction (LPC), and whole brain polynomial correction (WBPC)). Methods Measurements of the eddy current induced phase error from a static phantom were first obtained. In thirty healthy human subjects, the methods were then assessed in background tissue to determine if local phase offsets could be removed. Finally, the techniques were used to correct VFR measurements in cerebral vessels and compared statistically. Results In the phantom, phase error was measured to be <2.1 ml/s per pixel and the bias was reduced with the correction schemes. In background tissue, the bias was significantly reduced, by 65.6% (LBC), 58.4% (LPC) and 47.7% (WBPC) (p < 0.001 across all schemes). Correction did not lead to significantly different VFR measurements in the vessels (p = 0.997). In the vessel measurements, the three correction schemes led to flow measurement differences of -0.04 ± 0.05 ml/s, 0.09 ± 0.16 ml/s, and -0.02 ± 0.06 ml/s. Although there was an improvement in background measurements with correction, there was no statistical difference between the three correction schemes (p = 0.242 in background and p = 0.738 in vessels). Conclusions While eddy current induced phase errors can vary between hardware and sequence configurations, our results showed that the impact is small in a typical brain PC-MR protocol and does not have a significant effect on VFR measurements in cerebral vessels.
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Klug G, Reinstadler SJ, Feistritzer HJ, Kremser C, Schwaiger JP, Reindl M, Mair J, Müller S, Mayr A, Franz WM, Metzler B. Cardiac index after acute ST-segment elevation myocardial infarction measured with phase-contrast cardiac magnetic resonance imaging. Eur Radiol 2015; 26:1999-2008. [PMID: 26385805 DOI: 10.1007/s00330-015-4022-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2015] [Revised: 09/02/2015] [Accepted: 09/09/2015] [Indexed: 01/03/2023]
Abstract
OBJECTIVES Phase-contrast CMR (PC-CMR) might provide a fast and robust non-invasive determination of left ventricular function in patients after ST-segment elevation myocardial infarction (STEMI). METHODS Cine sequences in the left-ventricular (LV) short-axis and free-breathing, retrospectively gated PC-CMR were performed in 90 patients with first acute STEMI and 15 healthy volunteers. Inter- and intra-observer agreement was determined. The correlations of clinical variables (age, gender, ejection fraction, NT pro-brain natriuretic peptide [NT-proBNP] with cardiac index (CI) were calculated. RESULTS For CI, there was a strong agreement of cine CMR with PC-CMR in healthy volunteers (r: 0.82, mean difference: -0.14 l/min/m(2), error ± 23 %). Agreement was lower in STEMI patients (r: 0.61, mean difference: -0.17 l/min/m(2), error ± 32 %). In STEMI patients, CI measured with PC-CMR showed lower intra-observer (1 % vs. 9 %) and similar inter-observer variability (9 % vs. 12 %) compared to cine CMR. CI was significantly correlated with age, ejection fraction and NT-proBNP values in STEMI patients. DISCUSSION The agreement of PC-CMR and cine CMR for the determination of CI is lower in STEMI patients than in healthy volunteers. After acute STEMI, CI measured with PC-CMR decreases with age, LV ejection fraction and higher NT-proBNP. KEY POINTS • Cine CMR and PC-CMR correlate well in healthy volunteers. • Agreement is lower in STEMI patients. • Cardiac Output should be measured with one method longitudinally. • Cardiac output decreases with age after myocardial infarction.
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Affiliation(s)
- Gert Klug
- University Clinic of Internal Medicine III, Cardiology and Angiology, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria.
| | - Sebastian Johannes Reinstadler
- University Clinic of Internal Medicine III, Cardiology and Angiology, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria
| | - Hans-Josef Feistritzer
- University Clinic of Internal Medicine III, Cardiology and Angiology, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria
| | - Christian Kremser
- Department of Radiology, Medical University of Innsbruck, Innsbruck, Austria
| | - Johannes P Schwaiger
- University Clinic of Internal Medicine III, Cardiology and Angiology, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria
| | - Martin Reindl
- University Clinic of Internal Medicine III, Cardiology and Angiology, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria
| | - Johannes Mair
- University Clinic of Internal Medicine III, Cardiology and Angiology, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria
| | - Silvana Müller
- University Clinic of Internal Medicine III, Cardiology and Angiology, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria
| | - Agnes Mayr
- Department of Radiology, Medical University of Innsbruck, Innsbruck, Austria
| | - Wolfgang-Michael Franz
- University Clinic of Internal Medicine III, Cardiology and Angiology, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria
| | - Bernhard Metzler
- University Clinic of Internal Medicine III, Cardiology and Angiology, Medical University of Innsbruck, Anichstraße 35, 6020, Innsbruck, Austria
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Boye D, Springer O, Wassmer F, Scheidegger S, Remonda L, Berberat J. Effects of contour propagation and background corrections in different MRI flow software packages. Acta Radiol Open 2015; 4:2058460115589124. [PMID: 26346318 PMCID: PMC4548733 DOI: 10.1177/2058460115589124] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2014] [Accepted: 05/07/2015] [Indexed: 11/23/2022] Open
Abstract
Background Velocity-encoded magnetic resonance imaging (VENC-MRI) is a commonly used technique in cardiac examinations. This technique utilizes the phase shift properties of protons moving along a magnetic field gradient. VENC-MRI offers a unique way of measuring the severity of valve regurgitation by directly quantifying the regurgitation flow volume. Purpose To compare flow analysis results of different software programs and to assess the effect of background correction in sample patient cases. Material and Methods A phantom was built out of Polymethyl methacrylate (PMMA) which provides tubes of different diameters. These tubes can be connected to an external water circuit to generate a water flow inside the tubes. Expected absolute flow quantities inside the tubes were determined from preset tube- and flow-parameters. Different flow conditions were measured with a VENC-MRI sequence and the images evaluated using different software packages. In a second step six randomly selected patients showing different degrees of aortic insufficiency were evaluated in clinical terms. Results The contour propagation algorithms used in the software packages performed differently even on static phantom geometry. In terms of clinical evaluation the software packages performed similarly. Enabling background correction or leaving out manual correction of propagated contours changed results for severity of aortic insufficiency. Conclusion Turning on background correction and manual correction of propagated contours in MRI flow volume measurements is strongly recommended.
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Affiliation(s)
- D Boye
- Cantonal Hospital Aarau, Department of Neuroradiology, Aarau, Switzerland
| | - O Springer
- Cantonal Hospital Aarau, Department of Radiology, Aarau, Switzerland
| | - F Wassmer
- Zurich University of Applied Sciences, Institute of Applied Mathematics and Physics, Winterthur, Switzerland
| | - S Scheidegger
- Zurich University of Applied Sciences, Institute of Applied Mathematics and Physics, Winterthur, Switzerland
| | - L Remonda
- Cantonal Hospital Aarau, Department of Neuroradiology, Aarau, Switzerland
| | - J Berberat
- Cantonal Hospital Aarau, Department of Neuroradiology, Aarau, Switzerland
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Dyverfeldt P, Bissell M, Barker AJ, Bolger AF, Carlhäll CJ, Ebbers T, Francios CJ, Frydrychowicz A, Geiger J, Giese D, Hope MD, Kilner PJ, Kozerke S, Myerson S, Neubauer S, Wieben O, Markl M. 4D flow cardiovascular magnetic resonance consensus statement. J Cardiovasc Magn Reson 2015; 17:72. [PMID: 26257141 PMCID: PMC4530492 DOI: 10.1186/s12968-015-0174-5] [Citation(s) in RCA: 548] [Impact Index Per Article: 60.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2015] [Accepted: 07/17/2015] [Indexed: 02/07/2023] Open
Abstract
Pulsatile blood flow through the cavities of the heart and great vessels is time-varying and multidirectional. Access to all regions, phases and directions of cardiovascular flows has formerly been limited. Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has enabled more comprehensive access to such flows, with typical spatial resolution of 1.5×1.5×1.5 - 3×3×3 mm(3), typical temporal resolution of 30-40 ms, and acquisition times in the order of 5 to 25 min. This consensus paper is the work of physicists, physicians and biomedical engineers, active in the development and implementation of 4D Flow CMR, who have repeatedly met to share experience and ideas. The paper aims to assist understanding of acquisition and analysis methods, and their potential clinical applications with a focus on the heart and greater vessels. We describe that 4D Flow CMR can be clinically advantageous because placement of a single acquisition volume is straightforward and enables flow through any plane across it to be calculated retrospectively and with good accuracy. We also specify research and development goals that have yet to be satisfactorily achieved. Derived flow parameters, generally needing further development or validation for clinical use, include measurements of wall shear stress, pressure difference, turbulent kinetic energy, and intracardiac flow components. The dependence of measurement accuracy on acquisition parameters is considered, as are the uses of different visualization strategies for appropriate representation of time-varying multidirectional flow fields. Finally, we offer suggestions for more consistent, user-friendly implementation of 4D Flow CMR acquisition and data handling with a view to multicenter studies and more widespread adoption of the approach in routine clinical investigations.
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Affiliation(s)
- Petter Dyverfeldt
- Division of Cardiovascular Medicine, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
- Center for Medical Image Science and Visualization, Linköping University, Linköping, Sweden.
| | - Malenka Bissell
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford Centre for Clinical Magnetic Resonance Research, Oxford, UK.
| | - Alex J Barker
- Department of Radiology, Northwestern University, Chicago, USA.
| | - Ann F Bolger
- Division of Cardiovascular Medicine, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
- Center for Medical Image Science and Visualization, Linköping University, Linköping, Sweden.
- Department of Medicine, University of California San Francisco, San Francisco, CA, United States.
| | - Carl-Johan Carlhäll
- Division of Cardiovascular Medicine, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
- Center for Medical Image Science and Visualization, Linköping University, Linköping, Sweden.
- Department of Clinical Physiology, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
| | - Tino Ebbers
- Division of Cardiovascular Medicine, Department of Medical and Health Sciences, Linköping University, Linköping, Sweden.
- Center for Medical Image Science and Visualization, Linköping University, Linköping, Sweden.
| | | | - Alex Frydrychowicz
- Klinik für Radiologie und Nuklearmedizin, University Hospital Schleswig-Holstein, Campus Lübeck, Lübeck, Germany.
| | - Julia Geiger
- Department of Radiology, University Children's Hospital Zurich, Zurich, Switzerland.
| | - Daniel Giese
- Department of Radiology, University Hospital of Cologne, Cologne, Germany.
| | - Michael D Hope
- Department of Radiology, University of California San Francisco, San Francisco, CA, United States.
| | - Philip J Kilner
- NIHR Cardiovascular Biomedical Research Unit, Royal Brompton and Harefield NHS Foundation Trust, National Heart and Lung Institute, Imperial College, London, UK.
| | - Sebastian Kozerke
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland.
| | - Saul Myerson
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford Centre for Clinical Magnetic Resonance Research, Oxford, UK.
| | - Stefan Neubauer
- Division of Cardiovascular Medicine, Radcliffe Department of Medicine, University of Oxford Centre for Clinical Magnetic Resonance Research, Oxford, UK.
| | - Oliver Wieben
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA.
- Department of Medical Physics, University of Wisconsin, Madison, Wisconsin, USA.
| | - Michael Markl
- Department of Radiology, Northwestern University, Chicago, USA.
- Department of Biomedical Engineering, Northwestern University, Chicago, IL, USA.
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Nayak KS, Nielsen JF, Bernstein MA, Markl M, D Gatehouse P, M Botnar R, Saloner D, Lorenz C, Wen H, S Hu B, Epstein FH, N Oshinski J, Raman SV. Cardiovascular magnetic resonance phase contrast imaging. J Cardiovasc Magn Reson 2015; 17:71. [PMID: 26254979 PMCID: PMC4529988 DOI: 10.1186/s12968-015-0172-7] [Citation(s) in RCA: 154] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Accepted: 07/16/2015] [Indexed: 11/10/2022] Open
Abstract
Cardiovascular magnetic resonance (CMR) phase contrast imaging has undergone a wide range of changes with the development and availability of improved calibration procedures, visualization tools, and analysis methods. This article provides a comprehensive review of the current state-of-the-art in CMR phase contrast imaging methodology, clinical applications including summaries of past clinical performance, and emerging research and clinical applications that utilize today's latest technology.
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Affiliation(s)
- Krishna S Nayak
- Ming Hsieh Department of Electrical Engineering, University of Southern California, 3740 McClintock Ave, EEB 406, Los Angeles, California, 90089-2564, USA.
| | - Jon-Fredrik Nielsen
- Department of Biomedical Engineering, University of Michigan, Ann Arbor, MI, USA.
| | | | - Michael Markl
- Department of Radiology, Northwestern University, Chicago, IL, USA.
| | - Peter D Gatehouse
- Cardiovascular Biomedical Research Unit, Royal Brompton Hospital, London, UK.
| | - Rene M Botnar
- Cardiovascular Imaging, Imaging Sciences Division, Kings's College London, London, UK.
| | - David Saloner
- Department of Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, CA, USA.
| | - Christine Lorenz
- Center for Applied Medical Imaging, Siemens Corporation, Baltimore, MD, USA.
| | - Han Wen
- Imaging Physics Laboratory, National Heart Lung and Blood Institute, Bethesda, MD, USA.
| | - Bob S Hu
- Palo Alto Medical Foundation, Palo Alto, CA, USA.
| | - Frederick H Epstein
- Departments of Radiology and Biomedical Engineering, University of Virginia, Charlottesville, VA, USA.
| | - John N Oshinski
- Departments of Radiology and Biomedical Engineering, Emory University School of Medicine, Atlanta, GA, USA.
| | - Subha V Raman
- Division of Cardiovascular Medicine, The Ohio State University, Columbus, OH, USA.
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Santelli C, Loecher M, Busch J, Wieben O, Schaeffter T, Kozerke S. Accelerating 4D flow MRI by exploiting vector field divergence regularization. Magn Reson Med 2015; 75:115-25. [PMID: 25684112 DOI: 10.1002/mrm.25563] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2014] [Revised: 11/12/2014] [Accepted: 11/12/2014] [Indexed: 11/10/2022]
Abstract
PURPOSE To improve velocity vector field reconstruction from undersampled four-dimensional (4D) flow MRI by penalizing divergence of the measured flow field. THEORY AND METHODS Iterative image reconstruction in which magnitude and phase are regularized separately in alternating iterations was implemented. The approach allows incorporating prior knowledge of the flow field being imaged. In the present work, velocity data were regularized to reduce divergence, using either divergence-free wavelets (DFW) or a finite difference (FD) method using the ℓ1-norm of divergence and curl. The reconstruction methods were tested on a numerical phantom and in vivo data. Results of the DFW and FD approaches were compared with data obtained with standard compressed sensing (CS) reconstruction. RESULTS Relative to standard CS, directional errors of vector fields and divergence were reduced by 55-60% and 38-48% for three- and six-fold undersampled data with the DFW and FD methods. Velocity vector displays of the numerical phantom and in vivo data were found to be improved upon DFW or FD reconstruction. CONCLUSION Regularization of vector field divergence in image reconstruction from undersampled 4D flow data is a valuable approach to improve reconstruction accuracy of velocity vector fields.
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Affiliation(s)
- Claudio Santelli
- Imaging Sciences and Biomedical Engineering, King's College London, United Kingdom.,Institute for Biomedical Engineering, University and ETH Zurich, Switzerland
| | - Michael Loecher
- Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Julia Busch
- Institute for Biomedical Engineering, University and ETH Zurich, Switzerland
| | - Oliver Wieben
- Department of Medical Physics, University of Wisconsin-Madison, Madison, Wisconsin, USA.,Department of Radiology, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Tobias Schaeffter
- Imaging Sciences and Biomedical Engineering, King's College London, United Kingdom
| | - Sebastian Kozerke
- Imaging Sciences and Biomedical Engineering, King's College London, United Kingdom.,Institute for Biomedical Engineering, University and ETH Zurich, Switzerland
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Busch J, Vannesjo SJ, Barmet C, Pruessmann KP, Kozerke S. Analysis of temperature dependence of background phase errors in phase-contrast cardiovascular magnetic resonance. J Cardiovasc Magn Reson 2014; 16:97. [PMID: 25497004 PMCID: PMC4263200 DOI: 10.1186/s12968-014-0097-6] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2014] [Accepted: 11/14/2014] [Indexed: 11/16/2022] Open
Abstract
BACKGROUND The accuracy of phase-contrast cardiovascular magnetic resonance (PC-CMR) can be compromised by background phase errors. It is the objective of the present work to provide an analysis of the temperature dependence of background phase errors in PC-CMR by means of gradient mount temperature sensing and magnetic field monitoring. METHODS Background phase errors were measured for various temperatures of the gradient mount using magnetic field monitoring and validated in a static phantom. The effect of thermal changes during k-space acquisition was simulated and confirmed with measurements in a stationary phantom. RESULTS The temperature of the gradient mount was found to increase by 20-30 K during PC-CMR measurements of 6-12 min duration. Associated changes in background phase errors of up to 11% or 0.35 radian were measured at 10 cm from the magnet's iso-center as a result of first order offsets. Zeroth order phase errors exhibited little thermal dependence. CONCLUSIONS It is concluded that changes in gradient mount temperature significantly modify background phase errors during PC-CMR with high gradient duty cycle. Since temperature increases significantly during the first minutes of scanning the results presented are also of relevance for single-slice or multi-slice PC-CMR scans. The findings prompt for further studies to investigate advanced correction methods taking into account gradient temperature and/or the use of concurrent field-monitoring to map gradient-induced fields throughout the scan.
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Affiliation(s)
- Julia Busch
- />Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland
| | - S Johanna Vannesjo
- />Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland
| | - Christoph Barmet
- />Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland
- />Skope Magnetic Resonance Technologies, Zurich, Switzerland
| | - Klaas P Pruessmann
- />Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland
| | - Sebastian Kozerke
- />Institute for Biomedical Engineering, University of Zurich and ETH Zurich, Zurich, Switzerland
- />Division of Imaging Science and Biomedical Engineering, King’s College London, London, UK
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Aitken AP, Giese D, Tsoumpas C, Schleyer P, Kozerke S, Prieto C, Schaeffter T. Improved UTE-based attenuation correction for cranial PET-MR using dynamic magnetic field monitoring. Med Phys 2014; 41:012302. [PMID: 24387523 DOI: 10.1118/1.4837315] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
PURPOSE Ultrashort echo time (UTE) MRI has been proposed as a way to produce segmented attenuation maps for PET, as it provides contrast between bone, air, and soft tissue. However, UTE sequences require samples to be acquired during rapidly changing gradient fields, which makes the resulting images prone to eddy current artifacts. In this work it is demonstrated that this can lead to misclassification of tissues in segmented attenuation maps (AC maps) and that these effects can be corrected for by measuring the true k-space trajectories using a magnetic field camera. METHODS The k-space trajectories during a dual echo UTE sequence were measured using a dynamic magnetic field camera. UTE images were reconstructed using nominal trajectories and again using the measured trajectories. A numerical phantom was used to demonstrate the effect of reconstructing with incorrect trajectories. Images of an ovine leg phantom were reconstructed and segmented and the resulting attenuation maps were compared to a segmented map derived from a CT scan of the same phantom, using the Dice similarity measure. The feasibility of the proposed method was demonstrated in in vivo cranial imaging in five healthy volunteers. Simulated PET data were generated for one volunteer to show the impact of misclassifications on the PET reconstruction. RESULTS Images of the numerical phantom exhibited blurring and edge artifacts on the bone-tissue and air-tissue interfaces when nominal k-space trajectories were used, leading to misclassification of soft tissue as bone and misclassification of bone as air. Images of the tissue phantom and the in vivo cranial images exhibited the same artifacts. The artifacts were greatly reduced when the measured trajectories were used. For the tissue phantom, the Dice coefficient for bone in MR relative to CT was 0.616 using the nominal trajectories and 0.814 using the measured trajectories. The Dice coefficients for soft tissue were 0.933 and 0.934 for the nominal and measured cases, respectively. For air the corresponding figures were 0.991 and 0.993. Compared to an unattenuated reference image, the mean error in simulated PET uptake in the brain was 9.16% when AC maps derived from nominal trajectories was used, with errors in the SUV max for simulated lesions in the range of 7.17%-12.19%. Corresponding figures when AC maps derived from measured trajectories were used were 0.34% (mean error) and -0.21% to +1.81% (lesions). CONCLUSIONS Eddy current artifacts in UTE imaging can be corrected for by measuring the true k-space trajectories during a calibration scan and using them in subsequent image reconstructions. This improves the accuracy of segmented PET attenuation maps derived from UTE sequences and subsequent PET reconstruction.
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Affiliation(s)
- A P Aitken
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St. Thomas Hospital, London SE1 7EH, United Kingdom
| | - D Giese
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St. Thomas Hospital, London SE1 7EH, United Kingdom
| | - C Tsoumpas
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St. Thomas Hospital, London SE1 7EH, United Kingdom
| | - P Schleyer
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St. Thomas Hospital, London SE1 7EH, United Kingdom
| | - S Kozerke
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St. Thomas Hospital, London SE1 7EH, United Kingdom
| | - C Prieto
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St. Thomas Hospital, London SE1 7EH, United Kingdom
| | - T Schaeffter
- Department of Biomedical Engineering, Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St. Thomas Hospital, London SE1 7EH, United Kingdom
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38
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Chan RW, von Deuster C, Giese D, Stoeck CT, Harmer J, Aitken AP, Atkinson D, Kozerke S. Characterization and correction of eddy-current artifacts in unipolar and bipolar diffusion sequences using magnetic field monitoring. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2014; 244:74-84. [PMID: 24880880 DOI: 10.1016/j.jmr.2014.04.018] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2013] [Revised: 04/25/2014] [Accepted: 04/30/2014] [Indexed: 06/03/2023]
Abstract
Diffusion tensor imaging (DTI) of moving organs is gaining increasing attention but robust performance requires sequence modifications and dedicated correction methods to account for system imperfections. In this study, eddy currents in the "unipolar" Stejskal-Tanner and the velocity-compensated "bipolar" spin-echo diffusion sequences were investigated and corrected for using a magnetic field monitoring approach in combination with higher-order image reconstruction. From the field-camera measurements, increased levels of second-order eddy currents were quantified in the unipolar sequence relative to the bipolar diffusion sequence while zeroth and linear orders were found to be similar between both sequences. Second-order image reconstruction based on field-monitoring data resulted in reduced spatial misalignment artifacts and residual displacements of less than 0.43 mm and 0.29 mm (in the unipolar and bipolar sequences, respectively) after second-order eddy-current correction. Results demonstrate the need for second-order correction in unipolar encoding schemes but also show that bipolar sequences benefit from second-order reconstruction to correct for incomplete intrinsic cancellation of eddy-currents.
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Affiliation(s)
- Rachel W Chan
- Centre for Medical Imaging, University College London, London, United Kingdom.
| | - Constantin von Deuster
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom
| | - Daniel Giese
- Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom
| | - Christian T Stoeck
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
| | - Jack Harmer
- Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom
| | - Andrew P Aitken
- Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom
| | - David Atkinson
- Centre for Medical Imaging, University College London, London, United Kingdom
| | - Sebastian Kozerke
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland; Division of Imaging Sciences and Biomedical Engineering, King's College London, London, United Kingdom
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Giese D, Wong J, Greil GF, Buehrer M, Schaeffter T, Kozerke S. Towards highly accelerated Cartesian time-resolved 3D flow cardiovascular magnetic resonance in the clinical setting. J Cardiovasc Magn Reson 2014; 16:42. [PMID: 24942253 PMCID: PMC4230248 DOI: 10.1186/1532-429x-16-42] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2014] [Accepted: 05/02/2014] [Indexed: 11/17/2022] Open
Abstract
BACKGROUND The clinical applicability of time-resolved 3D flow cardiovascular magnetic resonance (CMR) remains compromised by the long scan times associated with phase-contrast imaging. The present work demonstrates the applicability of 8-fold acceleration of Cartesian time-resolved 3D flow CMR in 10 volunteers and in 9 patients with different congenital heart diseases (CHD). It is demonstrated that accelerated 3D flow CMR data acquisition and image reconstruction using k-t PCA (principal component analysis) can be implemented into clinical workflow and results are sufficiently accurate relative to conventional 2D flow CMR to permit for comprehensive flow quantification in CHD patients. METHODS The fidelity of k-t PCA was first investigated on retrospectively undersampled data for different acceleration factors and compared to k-t SENSE and fully sampled reference data. Subsequently, k-t PCA with 8-fold nominal undersampling was applied on 10 healthy volunteers and 9 CHD patients on a clinical 1.5 T MR scanner. Quantitative flow validation was performed in vessels of interest on the 3D flow datasets and compared to 2D through-plane flow acquisitions. Particle trace analysis was used to qualitatively visualise flow patterns in patients. RESULTS Accelerated time-resolved 3D flow data were successfully acquired in all subjects with 8-fold nominal scan acceleration. Nominal scan times excluding navigator efficiency were on the order of 6 min and 7 min in patients and volunteers. Mean differences in stroke volume in selected vessels of interest were 2.5 ± 8.4 ml and 1.63 ± 4.8 ml in volunteers and patients, respectively. Qualitative flow pattern analysis in the time-resolved 3D dataset revealed valuable insights into hemodynamics including circular and helical patterns as well as flow distributions and origin in the Fontan circulation. CONCLUSION Highly accelerated time-resolved 3D flow using k-t PCA is readily applicable in clinical routine protocols of CHD patients. Nominal scan times of 6 min are well tolerated and allow for quantitative and qualitative flow assessment in all great vessels.
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Affiliation(s)
- Daniel Giese
- Division of Imaging Sciences and Biomedical Engineering, King’s College London, London, UK
- Department of Radiology, University of Cologne, Cologne, Germany
| | - James Wong
- Division of Imaging Sciences and Biomedical Engineering, King’s College London, London, UK
| | - Gerald F Greil
- Division of Imaging Sciences and Biomedical Engineering, King’s College London, London, UK
| | - Martin Buehrer
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
| | - Tobias Schaeffter
- Division of Imaging Sciences and Biomedical Engineering, King’s College London, London, UK
| | - Sebastian Kozerke
- Division of Imaging Sciences and Biomedical Engineering, King’s College London, London, UK
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
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40
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Nilsson A, Revstedt J, Heiberg E, Ståhlberg F, Bloch KM. Volumetric velocity measurements in restricted geometries using spiral sampling: a phantom study. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2014; 28:103-18. [PMID: 24838252 DOI: 10.1007/s10334-014-0449-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/10/2014] [Revised: 03/28/2014] [Accepted: 04/24/2014] [Indexed: 10/25/2022]
Abstract
OBJECT The aim of this study was to evaluate the accuracy of maximum velocity measurements using volumetric phase-contrast imaging with spiral readouts in a stenotic flow phantom. MATERIALS AND METHODS In a phantom model, maximum velocity, flow, pressure gradient, and streamline visualizations were evaluated using volumetric phase-contrast magnetic resonance imaging (MRI) with velocity encoding in one (extending on current clinical practice) and three directions (for characterization of the flow field) using spiral readouts. Results of maximum velocity and pressure drop were compared to computational fluid dynamics (CFD) simulations, as well as corresponding low-echo-time (TE) Cartesian data. Flow was compared to 2D through-plane phase contrast (PC) upstream from the restriction. RESULTS Results obtained with 3D through-plane PC as well as 4D PC at shortest TE using a spiral readout showed excellent agreements with the maximum velocity values obtained with CFD (<1 % for both methods), while larger deviations were seen using Cartesian readouts (-2.3 and 13 %, respectively). Peak pressure drop calculations from 3D through-plane PC and 4D PC spiral sequences were respectively 14 and 13 % overestimated compared to CFD. CONCLUSION Identification of the maximum velocity location, as well as the accurate velocity quantification can be obtained in stenotic regions using short-TE spiral volumetric PC imaging.
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Affiliation(s)
- Anders Nilsson
- Department of Medical Radiation Physics, Lund University, Lund, Sweden,
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Lam A, Clement-Guinaudeau S, Padala M, Eisner RL, Thourani V, Vadnais D, Hurst S, Guyton RA, Oshinksi JN. Postsurgical hemodynamics of the aortic valve bypass operation evaluated with phase contrast magnetic resonance. J Magn Reson Imaging 2014; 40:899-905. [PMID: 24811700 DOI: 10.1002/jmri.24423] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2013] [Accepted: 08/28/2013] [Indexed: 11/06/2022] Open
Abstract
PURPOSE To characterize the postsurgical hemodynamics in aortic valve bypass (AVB) patients, and to determine the relationship between presurgical native aortic valve pressure gradient and postsurgical hemodynamics. MATERIALS AND METHODS Twenty patients scheduled for AVB surgery underwent presurgical transthoracic Doppler echocardiography to assess the degree of aortic stenosis and postsurgical cardiac magnetic resonance imaging (MRI) to acquire phase contrast magnetic resonance (PCMR) flow values along the ascending and descending aorta, and in the conduit. Net flow values were calculated from the PCMR images and compared to presurgical aortic valve pressure gradient measurements. RESULTS PCMR showed that: 1) The blood flow split between the aorta and the conduit was 35%:65% of cardiac output and 2) 60% of patients had net retrograde blood flow in the superior thoracic aorta over the cardiac cycle. Patients with presurgical pressure gradient (ΔP) > 45 mmHg had significantly less blood flow out of the native aorta than patients with ΔP < 45 mmHg, and had significantly more retrograde flow in the superior thoracic aorta postsurgery. CONCLUSION In patients undergoing AVB, presurgical aortic valve pressure gradient is associated with the volume of blood flow out the aorta and the direction of blood flow in the superior thoracic aorta after conduit addition as measured by PCMR.
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Affiliation(s)
- Adrian Lam
- Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, Georgia, USA
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Vannesjo SJ, Dietrich BE, Pavan M, Brunner DO, Wilm BJ, Barmet C, Pruessmann KP. Field camera measurements of gradient and shim impulse responses using frequency sweeps. Magn Reson Med 2013; 72:570-83. [PMID: 24105800 DOI: 10.1002/mrm.24934] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2013] [Revised: 07/19/2013] [Accepted: 08/01/2013] [Indexed: 11/09/2022]
Abstract
PURPOSE Applications of dynamic shimming require high field fidelity, and characterizing the shim field dynamics is therefore necessary. Modeling the system as linear and time-invariant, the purpose of this work was to measure the impulse response function with optimal sensitivity. THEORY AND METHODS Frequency-swept pulses as inputs are analyzed theoretically, showing that the sweep speed is a key factor for the measurement sensitivity. By adjusting the sweep speed it is possible to achieve any prescribed noise profile in the measured system response. Impulse response functions were obtained for the third-order shim system of a 7 Tesla whole-body MR scanner. Measurements of the shim fields were done with a dynamic field camera, yielding also cross-term responses. RESULTS The measured shim impulse response functions revealed system characteristics such as response bandwidth, eddy currents and specific resonances, possibly of mechanical origin. Field predictions based on the shim characterization were shown to agree well with directly measured fields, also in the cross-terms. CONCLUSION Frequency sweeps provide a flexible tool for shim or gradient system characterization. This may prove useful for applications involving dynamic shimming by yielding accurate estimates of the shim fields and a basis for setting shim pre-emphasis.
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Affiliation(s)
- S Johanna Vannesjo
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
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Tresoldi D, Cadioli M, Ponzini R, Esposito A, De Cobelli F, Morbiducci U, Rizzo G. Mapping aortic hemodynamics using 3D cine phase contrast magnetic resonance parallel imaging: Evaluation of an anisotropic diffusion filter. Magn Reson Med 2013; 71:1621-31. [DOI: 10.1002/mrm.24811] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Revised: 04/24/2013] [Accepted: 04/25/2013] [Indexed: 11/08/2022]
Affiliation(s)
- D. Tresoldi
- Institute of Molecular Bioimaging and Physiology, CNR; Segrate (Milan) Italy
- Bioengineering Department; Politecnico di Milano; Milan Italy
| | | | | | - A. Esposito
- Department of Radiology; Scientific Institute H. S. Raffaele; Milan Italy
| | - F. De Cobelli
- Department of Radiology; Scientific Institute H. S. Raffaele; Milan Italy
| | - U. Morbiducci
- Department of Mechanical and Aerospace Engineering; Politecnico di Torino; Turin Italy
| | - G. Rizzo
- Institute of Molecular Bioimaging and Physiology, CNR; Segrate (Milan) Italy
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Gatehouse PD, Rolf MP, Bloch KM, Graves MJ, Kilner PJ, Firmin DN, Hofman MBM. A multi-center inter-manufacturer study of the temporal stability of phase-contrast velocity mapping background offset errors. J Cardiovasc Magn Reson 2012; 14:72. [PMID: 23083397 PMCID: PMC3514147 DOI: 10.1186/1532-429x-14-72] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2011] [Accepted: 10/01/2012] [Indexed: 11/24/2022] Open
Abstract
BACKGROUND Phase-contrast velocity images often contain a background or baseline offset error, which adds an unknown offset to the measured velocities. For accurate flow measurements, this offset must be shown negligible or corrected. Some correction techniques depend on replicating the clinical flow acquisition using a uniform stationary phantom, in order to measure the baseline offset at the region of interest and subtract it from the clinical study. Such techniques assume that the background offset is stable over the time of a patient scan, or even longer if the phantom scans are acquired later, or derived from pre-stored background correction images. There is no published evidence regarding temporal stability of the background offset. METHODS This study assessed the temporal stability of the background offset on 3 different manufacturers' scanners over 8 weeks, using a retrospectively-gated phase-contrast cine acquisition with fixed parameters and at a fixed location, repeated 5 times in rapid succession each week. A significant offset was defined as 0.6 cm/s within 50 mm of isocenter, based upon an accuracy of 10% in a typical cardiac shunt measurement. RESULTS Over the 5 repeated cine acquisitions, temporal drift in the baseline offset was insignificant on two machines (0.3 cm/s, 0.2 cm/s), and marginally insignificant on the third machine (0.5 cm/s) due to an apparent heating effect. Over a longer timescale of 8 weeks, insignificant drift (0.4 cm/s) occurred on one, with larger drifts (0.9 cm/s, 0.6 cm/s) on the other machines. CONCLUSIONS During a typical patient study, background drift was insignificant. Extended high gradient power scanning with work requires care to avoid drift on some machines. Over the longer term of 8 weeks, significant drift is likely, preventing accurate correction by delayed phantom corrections or derivation from pre-stored background offset data.
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Affiliation(s)
| | - Marijn P Rolf
- VU University Medical Center, ICaR-VU, Amsterdam, Netherlands
| | | | | | | | | | - Mark BM Hofman
- VU University Medical Center, ICaR-VU, Amsterdam, Netherlands
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Vannesjo SJ, Haeberlin M, Kasper L, Pavan M, Wilm BJ, Barmet C, Pruessmann KP. Gradient system characterization by impulse response measurements with a dynamic field camera. Magn Reson Med 2012; 69:583-93. [PMID: 22499483 DOI: 10.1002/mrm.24263] [Citation(s) in RCA: 133] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2011] [Revised: 02/03/2012] [Accepted: 02/25/2012] [Indexed: 11/06/2022]
Abstract
This work demonstrates a fast, sensitive method of characterizing the dynamic performance of MR gradient systems. The accuracy of gradient time-courses is often compromised by field imperfections of various causes, including eddy currents and mechanical oscillations. Characterizing these perturbations is instrumental for corrections by pre-emphasis or post hoc signal processing. Herein, a gradient chain is treated as a linear time-invariant system, whose impulse response function is determined by measuring field responses to known gradient inputs. Triangular inputs are used to probe the system and response measurements are performed with a dynamic field camera consisting of NMR probes. In experiments on a whole-body MR system, it is shown that the proposed method yields impulse response functions of high temporal and spectral resolution. Besides basic properties such as bandwidth and delay, it also captures subtle features such as mechanically induced field oscillations. For validation, measured response functions were used to predict gradient field evolutions, which was achieved with an error below 0.2%. The field camera used records responses of various spatial orders simultaneously, rendering the method suitable also for studying cross-responses and dynamic shim systems. It thus holds promise for a range of applications, including pre-emphasis optimization, quality assurance, and image reconstruction.
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Affiliation(s)
- Signe J Vannesjo
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
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