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Walheim J, Dillinger H, Kozerke S. Multipoint 5D flow cardiovascular magnetic resonance - accelerated cardiac- and respiratory-motion resolved mapping of mean and turbulent velocities. J Cardiovasc Magn Reson 2019; 21:42. [PMID: 31331353 PMCID: PMC6647085 DOI: 10.1186/s12968-019-0549-0] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2018] [Accepted: 06/05/2019] [Indexed: 01/24/2023] Open
Abstract
BACKGROUND Volumetric quantification of mean and fluctuating velocity components of transient and turbulent flows promises a comprehensive characterization of valvular and aortic flow characteristics. Data acquisition using standard navigator-gated 4D Flow cardiovascular magnetic resonance (CMR) is time-consuming and actual scan times depend on the breathing pattern of the subject, limiting the applicability of the method in a clinical setting. We sought to develop a 5D Flow CMR framework which combines undersampled data acquisition including multipoint velocity encoding with low-rank image reconstruction to provide cardiac- and respiratory-motion resolved assessment of velocity maps and turbulent kinetic energy in fixed scan times. METHODS Data acquisition and data-driven motion state detection was performed using an undersampled Cartesian tiny Golden angle approach. Locally low-rank (LLR) reconstruction was implemented to exploit correlations among heart phases and respiratory motion states. To ensure accurate quantification of mean and turbulent velocities, a multipoint encoding scheme with two velocity encodings per direction was incorporated. Velocity-vector fields and turbulent kinetic energy (TKE) were obtained using a Bayesian approach maximizing the posterior probability given the measured data. The scan time of 5D Flow CMR was set to 4 min. 5D Flow CMR with acceleration factors of 19 .0 ± 0.21 (mean ± std) and velocity encodings (VENC) of 0.5 m/s and 1.5 m/s per axis was compared to navigator-gated 2x SENSE accelerated 4D Flow CMR with VENC = 1.5 m/s in 9 subjects. Peak velocities and peak flow were compared and magnitude images, velocity and TKE maps were assessed. RESULTS While net scan time of 5D Flow CMR was 4 min independent of individual breathing patterns, the scan times of the standard 4D Flow CMR protocol varied depending on the actual navigator gating efficiency and were 17.8 ± 3.9 min on average. Velocity vector fields derived from 5D Flow CMR in the end-expiratory state agreed well with data obtained from the navigated 4D protocol (normalized root-mean-square error 8.9 ± 2.1%). On average, peak velocities assessed with 5D Flow CMR were higher than for the 4D protocol (3.1 ± 4.4%). CONCLUSIONS Respiratory-motion resolved multipoint 5D Flow CMR allows mapping of mean and turbulent velocities in the aorta in 4 min.
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Affiliation(s)
- Jonas Walheim
- Institute for Biomedical Engineering, University and ETH Zurich, Gloriastrasse 35 8092, Zurich, Switzerland
| | - Hannes Dillinger
- Institute for Biomedical Engineering, University and ETH Zurich, Gloriastrasse 35 8092, Zurich, Switzerland
| | - Sebastian Kozerke
- Institute for Biomedical Engineering, University and ETH Zurich, Gloriastrasse 35 8092, Zurich, Switzerland
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Ma LE, Markl M, Chow K, Huh H, Forman C, Vali A, Greiser A, Carr J, Schnell S, Barker AJ, Jin N. Aortic 4D flow MRI in 2 minutes using compressed sensing, respiratory controlled adaptive k-space reordering, and inline reconstruction. Magn Reson Med 2019; 81:3675-3690. [PMID: 30803006 DOI: 10.1002/mrm.27684] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2018] [Revised: 01/14/2019] [Accepted: 01/15/2019] [Indexed: 01/09/2023]
Abstract
PURPOSE To evaluate the accuracy and feasibility of a free-breathing 4D flow technique using compressed sensing (CS), where 4D flow imaging of the thoracic aorta is performed in 2 min with inline image reconstruction on the MRI scanner in less than 5 min. METHODS The 10 in vitro 4D flow MRI scans were performed with different acceleration rates on a pulsatile flow phantom (9 CS acceleration factors [R = 5.4-14.1], 1 generalized autocalibrating partially parallel acquisition [GRAPPA] R = 2). Based on in vitro results, CS-accelerated 4D flow of the thoracic aorta was acquired in 20 healthy volunteers (38.3 ± 15.2 years old) and 11 patients with aortic disease (61.3 ± 15.1 years) with R = 7.7. A conventional 4D flow scan was acquired with matched spatial coverage and temporal resolution. RESULTS CS depicted similar hemodynamics to conventional 4D flow in vitro, and in vivo, with >70% reduction in scan time (volunteers: 1:52 ± 0:25 versus 7:25 ± 2:35 min). Net flow values were within 3.5% in healthy volunteers, and voxel-by-voxel comparison demonstrated good agreement. CS significantly underestimated peak velocities (vmax ) and peak flow (Qmax ) in both volunteers and patients (volunteers: vmax , -16.2% to -9.4%, Qmax : -11.6% to -2.9%, patients: vmax , -11.2% to -4.0%; Qmax , -10.2% to -5.8%). CONCLUSION Aortic 4D flow with CS is feasible in a two minute scan with less than 5 min for inline reconstruction. While net flow agreement was excellent, CS with R = 7.7 produced underestimation of Qmax and vmax ; however, these were generally within 13% of conventional 4D flow-derived values. This approach allows 4D flow to be feasible in clinical practice for comprehensive assessment of hemodynamics.
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Affiliation(s)
- Liliana E Ma
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois.,Department of Biomedical Engineering, Northwestern University, Chicago, Illinois
| | - Michael Markl
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois.,Department of Biomedical Engineering, Northwestern University, Chicago, Illinois
| | - Kelvin Chow
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois.,Cardiovascular MR R&D, Siemens Medical Solutions USA, Inc, Chicago, Illinois
| | - Hyungkyu Huh
- Daegu-Gyeongbuk Medical Innovation Foundation, Medical Device Development Center, Daegu, South Korea
| | | | - Alireza Vali
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois
| | | | - James Carr
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois
| | - Susanne Schnell
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois
| | - Alex J Barker
- Department of Radiology, Children's Hospital Colorado, University of Colorado, Anschutz Medical Campus, Denver, Colorado.,Department of Bioengineering, University of Colorado, Anschutz Medical Campus, Denver, Colorado
| | - Ning Jin
- Cardiovascular MR R&D, Siemens Medical Solutions USA, Inc, Cleveland, Ohio
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Garcia J, Barker AJ, Markl M. The Role of Imaging of Flow Patterns by 4D Flow MRI in Aortic Stenosis. JACC Cardiovasc Imaging 2019; 12:252-266. [DOI: 10.1016/j.jcmg.2018.10.034] [Citation(s) in RCA: 85] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/15/2018] [Revised: 10/16/2018] [Accepted: 10/19/2018] [Indexed: 11/30/2022]
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Wang L, Nie H, Wang Q, Zhang G, Li G, Bai L, Hua T, Wei S. Use of magnetic resonance imaging combined with gene analysis for the diagnosis of fetal congenital heart disease. BMC Med Imaging 2019; 19:12. [PMID: 30683072 PMCID: PMC6347844 DOI: 10.1186/s12880-019-0314-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Accepted: 01/16/2019] [Indexed: 12/17/2022] Open
Abstract
BACKGROUND Fetal deformity is a disease caused by abnormal chromosome structure, which may be influenced by genetic factors as well as the maternal and external environment. Magnetic resonance imaging (MRI) may be used to effectively diagnose fetus deformities. However it has been reported that gene analysis is a more accurate diagnostic method. The aim of the present study was to investigate the effectiveness of MRI in combination with gene analysis for the diagnosis of fetal congenital heart disease, a form of fetus deformity. METHODS MRI, array comparative genome hybridization analysis and fluorescence in situ hybridization were used to analyze the effectiveness of the two methods in a total of 78 pregnant women with suspected fetal congenital heart disease. RESULTS Our findings demonstrated that the combination of MRI and gene analysis resulted in significantly improved diagnostic accuracy, sensitivity and specificity for fetal congenital heart disease compared with either method alone. MRI combined with gene analysis confirmed 42 fetuses with pulmonary stenosis, 24 with aortic stenosis and 12 healthy fetuses, which was significantly improved compared with MRI or gene analysis alone. It was also observed that gene analysis was a more efficient method of diagnosis compared with MRI; however, the combination of the two methods was the most effective. CONCLUSION In conclusion, the results of the present study suggest that MRI combined with gene analysis may be a more effective diagnostic method for fetal congenital heart disease compared with the current protocol.
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Affiliation(s)
- Lishun Wang
- Department of Radiology, Maternity and Child Care Center of Qinhuangdao, Qinhuangdao Maternal and Child Health Hospital, Qinhuangdao, Hebei, 066000, People's Republic of China.
| | - Hongyan Nie
- Department of Ultrasound, Maternity and Child Care Center of Qinhuangdao, Qinhuangdao Maternal and Child Health Hospital, Qinhuangdao, Hebei, 066000, People's Republic of China
| | - Qichen Wang
- Department of Radiology, Maternity and Child Care Center of Qinhuangdao, Qinhuangdao Maternal and Child Health Hospital, Qinhuangdao, Hebei, 066000, People's Republic of China
| | - Guoliang Zhang
- Department of Radiology, Maternity and Child Care Center of Qinhuangdao, Qinhuangdao Maternal and Child Health Hospital, Qinhuangdao, Hebei, 066000, People's Republic of China
| | - Gang Li
- Department of Anesthesiology, Maternity and Child Care Center of Qinhuangdao, Qinhuangdao Maternal and Child Health Hospital, qinhuangdao, Hebei, 066000, People's Republic of China
| | - Liwei Bai
- Prenatal Diagnosis Center, Maternity and Child Care Center of Qinhuangdao, Qinhuangdao Maternal and Child Health Hospital, Qinhuangdao, Hebei, 066000, People's Republic of China
| | - Tianshu Hua
- Department of Epigenetics, Maternity and Child Care Center of Qinhuangdao, Qinhuangdao Maternal and Child Health Hospital, Qinhuangdao, Hebei, 066000, People's Republic of China
| | - Shuzhang Wei
- Department of Radiology, Maternity and Child Care Center of Liuzhou, Liuzhou, Guangxi Zhuang Autonomous Region, 545000, People's Republic of China
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Feneis JF, Kyubwa E, Atianzar K, Cheng JY, Alley MT, Vasanawala SS, Demaria AN, Hsiao A. 4D flow MRI quantification of mitral and tricuspid regurgitation: Reproducibility and consistency relative to conventional MRI. J Magn Reson Imaging 2018; 48:1147-1158. [PMID: 29638024 PMCID: PMC7962150 DOI: 10.1002/jmri.26040] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2018] [Accepted: 03/20/2018] [Indexed: 11/11/2022] Open
Abstract
BACKGROUND In patients with mitral or tricuspid valve regurgitation, evaluation of regurgitant severity is essential for determining the need for surgery. While transthoracic echocardiography is widely accessible, it has limited reproducibility for grading inlet valve regurgitation. Multiplanar cardiac MRI is the quantitative standard but requires specialized local expertise, and is thus not widely available. Volumetric 4D flow MRI has potential for quantitatively grading the severity of inlet valve regurgitation in adult patients. PURPOSE To evaluate the accuracy and reproducibility of volumetric 4D flow MRI for quantification of inlet valvular regurgitation compared to conventional multiplanar MRI, which may simplify and improve accessibility of cardiac MRI. STUDY TYPE This retrospective, HIPAA-compliant imaging-based comparison study was conducted at a single institution. SUBJECTS Twenty-one patients who underwent concurrent multiplanar and 4D flow cardiac MRI between April 2015 and January 2017. FIELD STRENGTH/SEQUENCES 3T; steady-state free-precession (SSFP), 2D phase contrast (2D-PC), and postcontrast 4D flow. ASSESSMENT We evaluated the intertechnique (4D flow vs. 2D-PC), intermethod (direct vs. indirect measurement), interobserver and intraobserver reproducibility of measurements of regurgitant flow volume (RFV), fraction (RF), and volume (RVol). STATISTICAL TESTS Statistical analysis included Pearson correlation, Bland-Altman statistics, and intraclass correlation coefficients. RESULTS There was high concordance between 4D flow and multiplanar MRI, whether using direct or indirect methods of quantifying regurgitation (r = 0.813-0.985). Direct interrogation of the regurgitant jet with 4D flow showed high intraobserver consistency (r = 0.976-0.999) and interobserver consistency (r = 0.861-0.992), and correlated well with traditional indirect measurements obtained as the difference between stroke volume and forward outlet valve flow. DATA CONCLUSION 4D flow MRI provides highly reproducible measurements of mitral and tricuspid regurgitant volume, and may be used in place of conventional multiplanar MRI. LEVEL OF EVIDENCE 4 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:1147-1158.
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Affiliation(s)
| | - Espoir Kyubwa
- Department of Radiology, UC San Diego, La Jolla, California, USA
| | - Kimberly Atianzar
- Department of Cardiovascular Disease, Swedish Heart and Vascular Institute, Seattle, WA
| | | | | | | | | | - Albert Hsiao
- Department of Radiology, UC San Diego, La Jolla, California, USA
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Walheim J, Gotschy A, Kozerke S. On the limitations of partial Fourier acquisition in phase-contrast MRI of turbulent kinetic energy. Magn Reson Med 2018; 81:514-523. [PMID: 30265753 DOI: 10.1002/mrm.27397] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Revised: 05/04/2018] [Accepted: 05/20/2018] [Indexed: 11/11/2022]
Abstract
PURPOSE To investigate limitations of partial Fourier acquisition in phase-contrast MRI of turbulent kinetic energy (TKE). METHODS To assess the validity of partial Fourier reconstruction of TKE and phase images, computational fluid dynamics data of mean and turbulent velocities in a stenotic U-bend phantom was used. Partial Fourier acquisition with 75% k-space coverage was simulated and TKE data were reconstructed using zero-filling, homodyne reconstruction, and the method of projections onto convex sets (POCS). Results were compared to data from fully sampled k-space and 75% symmetric sampling. In addition, compressed sensing (CS) reconstruction was compared for a standard variable density sampling pattern and a variable density sampling pattern combined with 75% partial Fourier. For illustration purposes, in vivo examples of velocity magnitude and TKE maps of aortic flow reconstructed with the different methods are provided. RESULTS In accordance with theory, partial Fourier reconstruction of TKE maps from phase-contrast data results in artifacts relative to fully sampled data. It is demonstrated that neither homodyne reconstruction nor POCS can improve reconstruction of TKE data with respect to zero-filling reconstruction when compared to ground-truth (RMS error: 4.70%, 4.34%, and 2.45% for homodyne, POCS, and zero-filling reconstruction of in vivo data, respectively). CS reconstruction from data acquired with partial Fourier did not recover the resolution loss incurred by partial Fourier sampling. CONCLUSION Partial Fourier reconstruction of TKE maps from phase-contrast data does not yield a benefit over zero-filling reconstruction. In consequence, symmetric sampling is preferred over partial Fourier acquisition for a given number of phase-encodes in phase-contrast MRI.
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Affiliation(s)
- Jonas Walheim
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
| | - Alexander Gotschy
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland.,Department of Cardiology, University Hospital Zurich, Zurich, Switzerland
| | - Sebastian Kozerke
- Institute for Biomedical Engineering, University and ETH Zurich, Zurich, Switzerland
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Zhou Z, Han F, Yoshida T, Nguyen KL, Finn JP, Hu P. Improved 4D cardiac functional assessment for pediatric patients using motion-weighted image reconstruction. MAGNETIC RESONANCE MATERIALS IN PHYSICS BIOLOGY AND MEDICINE 2018; 31:747-756. [PMID: 30043124 DOI: 10.1007/s10334-018-0694-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Revised: 07/06/2018] [Accepted: 07/08/2018] [Indexed: 01/07/2023]
Abstract
OBJECTIVE Our aim was to develop and evaluate a motion-weighted reconstruction technique for improved cardiac function assessment in 4D magnetic resonance imaging (MRI). MATERIALS AND METHODS A flat-topped, two-sided Gaussian kernel was used to weigh k-space data in each target cardiac phase and adjacent two temporal phases during the proposed phase-by-phase reconstruction algorithm. The proposed method (Strategy 3) was used to reconstruct 18 cardiac phases based on data acquired using a previously proposed technique [4D multiphase steady-state imaging with contrast enhancement (MUSIC) technique and its self-gated extension using rotating Cartesian k-space (ROCK-MUSIC) from 12 pediatric patients. As a comparison, the same data set was reconstructed into nine phases using a phase-by-phase method (Strategy 1), 18 phases using view sharing (Strategy 4), and 18 phases using a temporal regularized method (Strategy 2). Regional image sharpness and left ventricle volumetric measurements were used to compare the four reconstructions quantitatively. RESULTS Strategies 1 and 4 generated significantly sharper images of static structures (P ≤ 0.018) than Strategies 2 and 3 but significantly more blurry (P ≤ 0.021) images of the heart. Left ventricular volumetric measurements from the nine-phase reconstruction (Strategy 1) correlated moderately (r < 0.8) with the 2D cine, whereas the remaining three techniques had a higher correlation (r > 0.9). The computational burden of Strategy 2 was six times that of Strategy 3. CONCLUSION The proposed method of motion-weighted reconstruction improves temporal resolution in 4D cardiac imaging with a clinically practical workflow.
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Affiliation(s)
- Ziwu Zhou
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
- Department of Bioengineering, University of California, Los Angeles, CA, USA
| | - Fei Han
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
- Department of Bioengineering, University of California, Los Angeles, CA, USA
| | - Takegawa Yoshida
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
| | - Kim-Lien Nguyen
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
- Division of Cardiology, VA Greater Los Angeles Healthcare System, Los Angeles, CA, USA
| | - John Paul Finn
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, CA, USA
- Biomedical Physics Inter-Departmental Graduate Program, University of California, Los Angeles, CA, USA
| | - Peng Hu
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, CA, USA.
- Biomedical Physics Inter-Departmental Graduate Program, University of California, Los Angeles, CA, USA.
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, 300 UCLA Medical Plaza Suite B119, Los Angeles, CA, 90095, USA.
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Abstract
BACKGROUND Ferumoxytol, an "off-label" contrast agent, allows for better cardiac MRI quality as compared with gadolinium-based contrast agents. However, hypotension has been reported with the use of ferumoxytol for indications other than cardiac MRI. The purpose of our investigation was to evaluate the safety of ferumoxytol in children undergoing general anaesthesia for cardiac MRI. METHODS Medical records of children undergoing general anaesthesia for cardiac MRI were reviewed. Baseline demographic and medical characteristics, as well as imaging and anaesthetic duration and technique, were collected. The incidence of hypotension or other adverse events', need for vasoactive support, or airway intervention throughout the anaesthetic, was recorded. RESULTS A total of 95 patients were identified, 61 received ferumoxytol and 34 received gadolinium. There were no significant differences between groups with respect to age, weight, or baseline blood pressure. The incidence of low blood pressure - systolic or mean - after contrast administration did not differ between groups, and there was no difference in sustained hypotension or use of vasopressors between groups. One patient who received ferumoxytol had possible anaphylaxis. The image acquisition time (45 versus 68 min, p=0.002) and anaesthesia duration (100 versus 132 min, p=0.02) were shorter in the ferumoxytol group. CONCLUSION Transient low blood pressure was common in children undergoing cardiac MRI with anaesthesia, but the incidence of hypotension did not differ between ferumoxytol and gadolinium groups. The use of ferumoxytol was associated with significantly shorter scan time and anaesthesia duration, as well as a decreased need for airway intervention.
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Priya S, Thomas R, Nagpal P, Sharma A, Steigner M. Congenital anomalies of the aortic arch. Cardiovasc Diagn Ther 2018; 8:S26-S44. [PMID: 29850417 DOI: 10.21037/cdt.2017.10.15] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Congenital anomalies of the aortic arch include diverse subgroups of malformations that may be clinically silent or may present with severe respiratory or esophageal symptoms especially when associated with complete vascular rings. These anomalies may be isolated or may be associated with other congenital heart diseases. Volume rendered computed tomography (CT) and magnetic resonance angiography (MRA) help in preoperative surgical planning by providing information about the complex relationship of aortic arch and its branches to the trachea and esophagus. Three dimensional capabilities of both computed tomography angiography (CTA) and MRA are helpful in determining evidence of tracheal or esophageal compression or other high-risk features in patients with a complete vascular ring.
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Affiliation(s)
- Sarv Priya
- Division of Non-Invasive Cardiovascular Imaging, Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
| | - Richard Thomas
- Division of Non-Invasive Cardiovascular Imaging, Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
| | - Prashant Nagpal
- Department of Radiology, University of Iowa Hospitals and Clinics, Iowa, USA
| | - Arun Sharma
- Department of Cardiovascular Radiology, All India Institute of Medical Sciences, New Delhi, India
| | - Michael Steigner
- Division of Non-Invasive Cardiovascular Imaging, Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA, USA
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Masutani EM, Contijoch F, Kyubwa E, Cheng J, Alley MT, Vasanawala S, Hsiao A. Volumetric segmentation-free method for rapid visualization of vascular wall shear stress using 4D flow MRI. Magn Reson Med 2018. [PMID: 29516632 DOI: 10.1002/mrm.27159] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
PURPOSE To develop a rapid segmentation-free method to visualize and compute wall shear stress (WSS) throughout the aorta using 4D Flow MRI data. WSS is the drag force-per-area the vessel endothelium exerts on luminal blood; abnormal levels of WSS are associated with cardiovascular pathologies. Previous methods for computing WSS are bottlenecked by labor-intensive manual segmentation of vessel boundaries. A rapid automated segmentation-free method for computing WSS is presented. THEORY AND METHODS Shear stress is the dot-product of the viscous stress tensor and the inward normal vector. The inward normal vectors are approximated as the gradient of fluid speed at every voxel. Subsequently, a 4D map of shear stress is computed as the partial derivatives of velocity with respect to the inward normal vectors. We highlight the shear stress near the wall by fusing visualization with edge-emphasized anatomical data. RESULTS As a proof-of-concept, four cases with aortic pathologies are presented. Visualization allows for rapid localization of pathologic WSS. Subsequent analysis of these pathological regions enables quantification of WSS. Average WSS during peak systole measures approximately 50-60 cPa in nonpathological regions of the aorta and is elevated in regions of stenosis, coarctation, and dissection. WSS is reduced in regions of aneurysm. CONCLUSION A volumetric technique for calculation and visualization of WSS from 4D Flow MRI data is presented. Traditional labor-intensive methods for WSS rely on explicit manual segmentation of vessel boundaries before visualization. This automated volumetric strategy for visualization and quantification of WSS may facilitate its clinical translation.
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Affiliation(s)
- Evan M Masutani
- Medical Scientist Training Program, University of California, San Diego, La Jolla, California.,Department of Medicine, University of California, San Diego, La Jolla, California
| | - Francisco Contijoch
- Department of Bioengineering, University of California, San Diego, La Jolla, California.,Department of Radiology, University of California, San Diego, La Jolla, California
| | - Espoir Kyubwa
- Medical Scientist Training Program, University of California, San Diego, La Jolla, California.,Department of Medicine, University of California, San Diego, La Jolla, California
| | - Joseph Cheng
- Department of Radiology, Stanford University, Stanford, California
| | - Marcus T Alley
- Department of Radiology, Stanford University, Stanford, California
| | | | - Albert Hsiao
- Department of Radiology, University of California, San Diego, La Jolla, California
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Pelvic Blood Flow Predicts Fibroid Volume and Embolic Required for Uterine Fibroid Embolization: A Pilot Study With 4D Flow MR Angiography. AJR Am J Roentgenol 2017; 210:189-200. [PMID: 29090998 DOI: 10.2214/ajr.17.18127] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
OBJECTIVE We report here an initial experience using 4D flow MRI in pelvic imaging-specifically, in imaging uterine fibroids. We hypothesized that blood flow might correlate with fibroid volume and that quantifying blood flow might help to predict the amount of embolic required to achieve stasis at subsequent uterine fibroid embolization (UFE). MATERIALS AND METHODS Thirty-three patients with uterine fibroids and seven control subjects underwent pelvic MRI with 4D flow imaging. Of the patients with fibroids, 10 underwent 4D flow imaging before UFE and seven after UFE; in the remaining 16 patients with fibroids, UFE had yet to be performed. Four-dimensional flow measurements were performed using Arterys CV Flow. The flow fraction of the internal iliac artery was expressed as the ratio of internal iliac artery flow to external iliac artery flow and was compared between groups. The flow ratios between the internal iliac arteries on each side were calculated. Fibroid volume versus internal iliac flow fraction, embolic volume versus internal iliac flow fraction, and embolic volume ratio between sides versus the ratio of internal iliac artery flows between sides were compared. RESULTS The mean internal iliac flow fraction was significantly higher in the 26 patients who underwent imaging before UFE (mean ± standard error, 0.78 ± 0.06) than in the seven patients who underwent imaging after UFE (0.48 ± 0.07, p < 0.01) and in the seven control patients without fibroids (0.48 ± 0.08, p < 0.0001). The internal iliac flow fraction correlated well with fibroid volumes before UFE (r = 0.7754, p < 0.0001) and did not correlate with fibroid volumes after UFE (r = -0.3051, p = 0.51). The ratio of embolic required to achieve stasis between sides showed a modest correlation with the ratio of internal iliac flow (r = 0.6776, p = 0.03). CONCLUSION Internal iliac flow measured by 4D flow MRI correlates with fibroid volume and is predictive of the ratio of embolic required to achieve stasis on each side at subsequent UFE and may be useful for preprocedural evaluation of patients with uterine fibroids.
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Comprehensive Multi-Dimensional MRI for the Simultaneous Assessment of Cardiopulmonary Anatomy and Physiology. Sci Rep 2017; 7:5330. [PMID: 28706270 PMCID: PMC5509743 DOI: 10.1038/s41598-017-04676-8] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Accepted: 05/18/2017] [Indexed: 01/22/2023] Open
Abstract
Diagnostic testing often assesses the cardiovascular or respiratory systems in isolation, ignoring the major pathophysiologic interactions between the systems in many diseases. When both systems are assessed currently, multiple modalities are utilized in costly fashion with burdensome logistics and decreased accessibility. Thus, we have developed a new acquisition and reconstruction paradigm using the flexibility of MRI to enable a comprehensive exam from a single 5-15 min scan. We constructed a compressive-sensing approach to pseudo-randomly acquire highly subsampled, multi-dimensionally-encoded and time-stamped data from which we reconstruct volumetric cardiac and respiratory motion phases, contrast-agent dynamics, and blood flow velocity fields. The proposed method, named XD flow, is demonstrated for (a) evaluating congenital heart disease, where the impact of bulk motion is reduced in a non-sedated neonatal patient and (b) where the observation of the impact of respiration on flow is necessary for diagnostics; (c) cardiopulmonary imaging, where cardiovascular flow, function, and anatomy information is needed along with pulmonary perfusion quantification; and in (d) renal function imaging, where blood velocities and glomerular filtration rates are simultaneously measured, which highlights the generality of the technique. XD flow has the ability to improve quantification and to provide additional data for patient diagnosis for comprehensive evaluations.
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Toth GB, Varallyay CG, Horvath A, Bashir MR, Choyke PL, Daldrup-Link HE, Dosa E, Finn JP, Gahramanov S, Harisinghani M, Macdougall I, Neuwelt A, Vasanawala SS, Ambady P, Barajas R, Cetas JS, Ciporen J, DeLoughery TJ, Doolittle ND, Fu R, Grinstead J, Guimaraes AR, Hamilton BE, Li X, McConnell HL, Muldoon LL, Nesbit G, Netto JP, Petterson D, Rooney WD, Schwartz D, Szidonya L, Neuwelt EA. Current and potential imaging applications of ferumoxytol for magnetic resonance imaging. Kidney Int 2017; 92:47-66. [PMID: 28434822 PMCID: PMC5505659 DOI: 10.1016/j.kint.2016.12.037] [Citation(s) in RCA: 204] [Impact Index Per Article: 29.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2016] [Revised: 11/17/2016] [Accepted: 12/06/2016] [Indexed: 01/18/2023]
Abstract
Contrast-enhanced magnetic resonance imaging is a commonly used diagnostic tool. Compared with standard gadolinium-based contrast agents, ferumoxytol (Feraheme, AMAG Pharmaceuticals, Waltham, MA), used as an alternative contrast medium, is feasible in patients with impaired renal function. Other attractive imaging features of i.v. ferumoxytol include a prolonged blood pool phase and delayed intracellular uptake. With its unique pharmacologic, metabolic, and imaging properties, ferumoxytol may play a crucial role in future magnetic resonance imaging of the central nervous system, various organs outside the central nervous system, and the cardiovascular system. Preclinical and clinical studies have demonstrated the overall safety and effectiveness of this novel contrast agent, with rarely occurring anaphylactoid reactions. The purpose of this review is to describe the general and organ-specific properties of ferumoxytol, as well as the advantages and potential pitfalls associated with its use in magnetic resonance imaging. To more fully demonstrate the applications of ferumoxytol throughout the body, an imaging atlas was created and is available online as supplementary material.
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Affiliation(s)
- Gerda B Toth
- Department of Neurology, Oregon Health & Science University, Portland, Oregon, USA
| | - Csanad G Varallyay
- Department of Radiology, Oregon Health & Science University, Portland, Oregon, USA
| | - Andrea Horvath
- Department of Neurology, Oregon Health & Science University, Portland, Oregon, USA
| | - Mustafa R Bashir
- Department of Radiology, Duke University Medical Center, 3808, Durham, North Carolina, USA; Center for Advanced Magnetic Resonance Development, Duke University Medical Center, Durham, North Carolina, USA
| | - Peter L Choyke
- Molecular Imaging Program, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Heike E Daldrup-Link
- Department of Radiology, Section of Pediatric Radiology, Lucile Packard Children's Hospital, Stanford University, 725 Welch Rd, Stanford, California, USA
| | - Edit Dosa
- Heart and Vascular Center, Semmelweis University, Budapest, Hungary
| | - John Paul Finn
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, California, USA
| | - Seymur Gahramanov
- Department of Neurosurgery, University of New Mexico Health Sciences Center, Albuquerque, New Mexico, USA
| | - Mukesh Harisinghani
- Department of Radiology, Harvard Medical School, Massachusetts General Hospital, Boston, Massachusetts, USA
| | - Iain Macdougall
- Department of Renal Medicine, King's College Hospital, London, UK
| | - Alexander Neuwelt
- Division of Medical Oncology, University of Colorado Denver, Aurora, Colorado, USA
| | | | - Prakash Ambady
- Department of Neurology, Oregon Health & Science University, Portland, Oregon, USA
| | - Ramon Barajas
- Department of Radiology, Oregon Health & Science University, Portland, Oregon, USA
| | - Justin S Cetas
- Department of Neurosurgery, Oregon Health & Science University, Portland, Oregon, USA
| | - Jeremy Ciporen
- Department of Neurosurgery, Oregon Health & Science University, Portland, Oregon, USA
| | - Thomas J DeLoughery
- Department of Hematology and Medical Oncology, Oregon Health & Science University, Portland, Oregon, USA
| | - Nancy D Doolittle
- Department of Neurology, Oregon Health & Science University, Portland, Oregon, USA
| | - Rongwei Fu
- School of Public Health, Oregon Health & Science University, Portland, Oregon, USA; Department of Medical Informatics and Clinical Epidemiology, Oregon Health & Science University, Portland, Oregon, USA
| | | | | | - Bronwyn E Hamilton
- Department of Radiology, Oregon Health & Science University, Portland, Oregon, USA
| | - Xin Li
- Advanced Imaging Research Center, Oregon Health & Science University, Portland, Oregon, USA
| | - Heather L McConnell
- Department of Neurology, Oregon Health & Science University, Portland, Oregon, USA
| | - Leslie L Muldoon
- Department of Neurology, Oregon Health & Science University, Portland, Oregon, USA
| | - Gary Nesbit
- Department of Radiology, Oregon Health & Science University, Portland, Oregon, USA
| | - Joao P Netto
- Department of Neurology, Oregon Health & Science University, Portland, Oregon, USA; Department of Radiology, Oregon Health & Science University, Portland, Oregon, USA
| | - David Petterson
- Department of Radiology, Oregon Health & Science University, Portland, Oregon, USA
| | - William D Rooney
- Advanced Imaging Research Center, Oregon Health & Science University, Portland, Oregon, USA
| | - Daniel Schwartz
- Department of Neurology, Oregon Health & Science University, Portland, Oregon, USA; Advanced Imaging Research Center, Oregon Health & Science University, Portland, Oregon, USA
| | - Laszlo Szidonya
- Department of Neurology, Oregon Health & Science University, Portland, Oregon, USA
| | - Edward A Neuwelt
- Department of Neurology, Oregon Health & Science University, Portland, Oregon, USA; Department of Neurosurgery, Oregon Health & Science University, Portland, Oregon, USA; Portland Veterans Affairs Medical Center, Portland, Oregon, USA.
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Zucker EJ, Cheng JY, Haldipur A, Carl M, Vasanawala SS. Free-breathing pediatric chest MRI: Performance of self-navigated golden-angle ordered conical ultrashort echo time acquisition. J Magn Reson Imaging 2017; 47:200-209. [PMID: 28570032 DOI: 10.1002/jmri.25776] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2017] [Accepted: 05/09/2017] [Indexed: 12/18/2022] Open
Abstract
PURPOSE To assess the feasibility and performance of conical k-space trajectory free-breathing ultrashort echo time (UTE) chest magnetic resonance imaging (MRI) versus four-dimensional (4D) flow and effects of 50% data subsampling and soft-gated motion correction. MATERIALS AND METHODS Thirty-two consecutive children who underwent both 4D flow and UTE ferumoxytol-enhanced chest MR (mean age: 5.4 years, range: 6 days to 15.7 years) in one 3T exam were recruited. From UTE k-space data, three image sets were reconstructed: 1) one with all data, 2) one using the first 50% of data, and 3) a final set with soft-gating motion correction, leveraging the signal magnitude immediately after each excitation. Two radiologists in blinded fashion independently scored image quality of anatomical landmarks on a 5-point scale. Ratings were compared using Wilcoxon rank-sum, Wilcoxon signed-ranks, and Kruskal-Wallis tests. Interobserver agreement was assessed with the intraclass correlation coefficient (ICC). RESULTS For fully sampled UTE, mean scores for all structures were ≥4 (good-excellent). Full UTE surpassed 4D flow for lungs and airways (P < 0.001), with similar pulmonary artery (PA) quality (P = 0.62). 50% subsampling only slightly degraded all landmarks (P < 0.001), as did motion correction. Subsegmental PA visualization was possible in >93% scans for all techniques (P = 0.27). Interobserver agreement was excellent for combined scores (ICC = 0.83). CONCLUSION High-quality free-breathing conical UTE chest MR is feasible, surpassing 4D flow for lungs and airways, with equivalent PA visualization. Data subsampling only mildly degraded images, favoring lesser scan times. Soft-gating motion correction overall did not improve image quality. LEVEL OF EVIDENCE 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:200-209.
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Affiliation(s)
- Evan J Zucker
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Joseph Y Cheng
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Anshul Haldipur
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Michael Carl
- Applied Science Laboratory, GE Healthcare, San Diego, California, USA
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Moghari MH, Uecker M, Roujol S, Sabbagh M, Geva T, Powell AJ. Accelerated whole-heart MR angiography using a variable-density poisson-disc undersampling pattern and compressed sensing reconstruction. Magn Reson Med 2017; 79:761-769. [PMID: 28497620 DOI: 10.1002/mrm.26730] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2016] [Revised: 03/09/2017] [Accepted: 04/02/2017] [Indexed: 11/07/2022]
Abstract
PURPOSE To accelerate whole-heart three-dimension MR angiography (MRA) by using a variable-density Poisson-disc undersampling pattern and a compressed sensing (CS) reconstruction algorithm, and compare the results with sensitivity encoding (SENSE). METHODS For whole-heart MRA, a prospective variable-density Poisson-disc k-space undersampling pattern was developed in which 1-2% of central part of k-space was fully sampled, and sampling in the remainder decreased exponentially toward the periphery. The undersampled data were then estimated using CS reconstruction. In patients, images using this sequence with an undersampling rate of ≈6 were compared with those using a SENSE rate of 2 (n = 15) and a SENSE rate of 6 (n = 13). RESULTS Compared with SENSE rate 2, CS rate 6 images had similar objective border sharpness, significantly lower subjective image quality scores at all four locations (all P < 0.01), and shorter scan times (P < 0.05). Compared with SENSE rate 6, CS rate 6 had similar objective border sharpness at all four locations, significantly better subjective image quality scores at three of four locations (all P < 0.01), and similar scan times (P = 0.24). CONCLUSION Compared with SENSE with a comparable acceleration rate, a variable-density Poisson-disc undersampling pattern and CS reconstruction achieved better subjective image quality and similar border sharpness. Magn Reson Med 79:761-769, 2018. © 2017 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Mehdi H Moghari
- Department of Cardiology, Boston Children's Hospital, and the Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA
| | - Martin Uecker
- German Center for Cardiovascular Research (DZHK), Partner Site Göttingen, Germany, and Department of Diagnostic and Interventional Radiology, University Medical Center, Göttingen, Germany
| | - Sébastien Roujol
- Division of Imaging Sciences and Biomedical Engineering, King's College London, King's Health Partners, St. Thomas' Hospital, London, United Kingdom
| | - Majid Sabbagh
- Department of Electrical and Computer Engineering, Northeastern University, Boston, Massachusetts, USA
| | - Tal Geva
- Department of Cardiology, Boston Children's Hospital, and the Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA
| | - Andrew J Powell
- Department of Cardiology, Boston Children's Hospital, and the Department of Pediatrics, Harvard Medical School, Boston, Massachusetts, USA
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Nguyen KL, Han F, Zhou Z, Brunengraber DZ, Ayad I, Levi DS, Satou GM, Reemtsen BL, Hu P, Finn JP. 4D MUSIC CMR: value-based imaging of neonates and infants with congenital heart disease. J Cardiovasc Magn Reson 2017; 19:40. [PMID: 28366171 PMCID: PMC5376692 DOI: 10.1186/s12968-017-0352-8] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2016] [Accepted: 03/03/2017] [Indexed: 12/05/2022] Open
Abstract
BACKGROUND 4D Multiphase Steady State Imaging with Contrast (MUSIC) acquires high-resolution volumetric images of the beating heart during uninterrupted ventilation. We aim to evaluate the diagnostic performance and clinical impact of 4D MUSIC in a cohort of neonates and infants with congenital heart disease (CHD). METHODS Forty consecutive neonates and infants with CHD (age range 2 days to 2 years, weight 1 to 13 kg) underwent 3.0 T CMR with ferumoxytol enhancement (FE) at a single institution. Independently, two readers graded the diagnostic image quality of intra-cardiac structures and related vascular segments on FE-MUSIC and breath held FE-CMRA images using a four-point scale. Correlation of the CMR findings with surgery and other imaging modalities was performed in all patients. Clinical impact was evaluated in consensus with referring surgeons and cardiologists. One point was given for each of five key outcome measures: 1) change in overall management, 2) change in surgical approach, 3) reduction in the need for diagnostic catheterization, 4) improved assessment of risk-to-benefit for planned intervention and discussion with parents, 5) accurate pre-procedural roadmap. RESULTS All FE-CMR studies were completed successfully, safely and without adverse events. On a four-point scale, the average FE-MUSIC image quality scores were >3.5 for intra-cardiac structures and >3.0 for coronary arteries. Intra-cardiac morphology and vascular anatomy were well visualized with good interobserver agreement (r = 0.46). Correspondence between the findings on MUSIC, surgery, correlative imaging and autopsy was excellent. The average clinical impact score was 4.2 ± 0.9. In five patients with discordant findings on echo/MUSIC (n = 5) and catheter angiography/MUSIC (n = 1), findings on FE-MUSIC were shown to be accurate at autopsy (n = 1) and surgery (n = 4). The decision to undertake biventricular vs univentricular repair was amended in 2 patients based on FE-MUSIC findings. Plans for surgical approaches which would have involved circulatory arrest were amended in two of 28 surgical cases. In all 28 cases requiring procedural intervention, FE-MUSIC provided accurate dynamic 3D roadmaps and more confident risk-to-benefit assessments for proposed interventions. CONCLUSIONS FE-MUSIC CMR has high clinical impact by providing accurate, high quality, simple and safe dynamic 3D imaging of cardiac and vascular anatomy in neonates and infants with CHD. The findings influenced patient management in a positive manner.
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Affiliation(s)
- Kim-Lien Nguyen
- Diagnostic Cardiovascular Imaging Laboratory, Department of Radiological Sciences, David Geffen School of Medicine at UCLA, Los Angeles, CA USA
- Division of Cardiology, David Geffen School of Medicine at UCLA and VA Greater Los Angeles Healthcare System, Los Angeles, CA USA
| | - Fei Han
- Diagnostic Cardiovascular Imaging Laboratory, Department of Radiological Sciences, David Geffen School of Medicine at UCLA, Los Angeles, CA USA
- Department of Biomedical Physics, University of California, Los Angeles, CA USA
- Department of Radiological Sciences, University of California at Los Angeles, Peter V. Ueberroth Building Suite 3371, 10945 Le Conte Ave., Los Angeles, CA 90095-7206 USA
| | - Ziwu Zhou
- Diagnostic Cardiovascular Imaging Laboratory, Department of Radiological Sciences, David Geffen School of Medicine at UCLA, Los Angeles, CA USA
- Department of Biomedical Physics, University of California, Los Angeles, CA USA
- Department of Radiological Sciences, University of California at Los Angeles, Peter V. Ueberroth Building Suite 3371, 10945 Le Conte Ave., Los Angeles, CA 90095-7206 USA
| | - Daniel Z. Brunengraber
- Diagnostic Cardiovascular Imaging Laboratory, Department of Radiological Sciences, David Geffen School of Medicine at UCLA, Los Angeles, CA USA
- Department of Radiological Sciences, University of California at Los Angeles, Peter V. Ueberroth Building Suite 3371, 10945 Le Conte Ave., Los Angeles, CA 90095-7206 USA
| | - Ihab Ayad
- Department of Anesthesiology, David Geffen School of Medicine at UCLA, Los Angeles, CA USA
| | - Daniel S. Levi
- Division of Pediatric Cardiology, David Geffen School of Medicine at UCLA, Los Angeles, CA USA
| | - Gary M. Satou
- Division of Pediatric Cardiology, David Geffen School of Medicine at UCLA, Los Angeles, CA USA
| | - Brian L. Reemtsen
- Division of Cardiothoracic Surgery, David Geffen School of Medicine at UCLA, Los Angeles, CA USA
| | - Peng Hu
- Diagnostic Cardiovascular Imaging Laboratory, Department of Radiological Sciences, David Geffen School of Medicine at UCLA, Los Angeles, CA USA
- Department of Biomedical Physics, University of California, Los Angeles, CA USA
- Department of Radiological Sciences, University of California at Los Angeles, Peter V. Ueberroth Building Suite 3371, 10945 Le Conte Ave., Los Angeles, CA 90095-7206 USA
| | - J. Paul Finn
- Diagnostic Cardiovascular Imaging Laboratory, Department of Radiological Sciences, David Geffen School of Medicine at UCLA, Los Angeles, CA USA
- Department of Biomedical Physics, University of California, Los Angeles, CA USA
- Department of Radiological Sciences, University of California at Los Angeles, Peter V. Ueberroth Building Suite 3371, 10945 Le Conte Ave., Los Angeles, CA 90095-7206 USA
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68
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Dwork N, Lasry EM, Pauly JM, Balbás J. Formulation of image fusion as a constrained least squares optimization problem. J Med Imaging (Bellingham) 2017; 4:014003. [PMID: 28331885 DOI: 10.1117/1.jmi.4.1.014003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Accepted: 02/08/2017] [Indexed: 12/13/2022] Open
Abstract
Fusing a lower resolution color image with a higher resolution monochrome image is a common practice in medical imaging. By incorporating spatial context and/or improving the signal-to-noise ratio, it provides clinicians with a single frame of the most complete information for diagnosis. In this paper, image fusion is formulated as a convex optimization problem that avoids image decomposition and permits operations at the pixel level. This results in a highly efficient and embarrassingly parallelizable algorithm based on widely available robust and simple numerical methods that realizes the fused image as the global minimizer of the convex optimization problem.
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Affiliation(s)
- Nicholas Dwork
- Stanford University , Department of Electrical Engineering, Stanford, California, United States
| | - Eric M Lasry
- Stanford University , Pre-Collegiate Summer Institutes, Stanford, California, United States
| | - John M Pauly
- Stanford University , Department of Electrical Engineering, Stanford, California, United States
| | - Jorge Balbás
- California State University in Northridge , Department of Mathematics, Northridge, California, United States
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Bollache E, Barker AJ, Dolan RS, Carr JC, van Ooij P, Ahmadian R, Powell A, Collins JD, Geiger J, Markl M. k-t accelerated aortic 4D flow MRI in under two minutes: Feasibility and impact of resolution, k-space sampling patterns, and respiratory navigator gating on hemodynamic measurements. Magn Reson Med 2017; 79:195-207. [PMID: 28266062 DOI: 10.1002/mrm.26661] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Revised: 02/08/2017] [Accepted: 02/08/2017] [Indexed: 01/29/2023]
Abstract
PURPOSE To assess the performance of highly accelerated free-breathing aortic four-dimensional (4D) flow MRI acquired in under 2 minutes compared to conventional respiratory gated 4D flow. METHODS Eight k-t accelerated nongated 4D flow MRI (parallel MRI with extended and averaged generalized autocalibrating partially parallel acquisition kernels [PEAK GRAPPA], R = 5, TRes = 67.2 ms) using four ky -kz Cartesian sampling patterns (linear, center-out, out-center-out, random) and two spatial resolutions (SRes1 = 3.5 × 2.3 × 2.6 mm3 , SRes2 = 4.5 × 2.3 × 2.6 mm3 ) were compared in vitro (aortic coarctation flow phantom) and in 10 healthy volunteers, to conventional 4D flow (16 mm-navigator acceptance window; R = 2; TRes = 39.2 ms; SRes = 3.2 × 2.3 × 2.4 mm3 ). The best k-t accelerated approach was further assessed in 10 patients with aortic disease. RESULTS The k-t accelerated in vitro aortic peak flow (Qmax), net flow (Qnet), and peak velocity (Vmax) were lower than conventional 4D flow indices by ≤4.7%, ≤ 11%, and ≤22%, respectively. In vivo k-t accelerated acquisitions were significantly shorter but showed a trend to lower image quality compared to conventional 4D flow. Hemodynamic indices for linear and out-center-out k-space samplings were in agreement with conventional 4D flow (Qmax ≤ 13%, Qnet ≤ 13%, Vmax ≤ 17%, P > 0.05). CONCLUSION Aortic 4D flow MRI in under 2 minutes is feasible with moderate underestimation of flow indices. Differences in k-space sampling patterns suggest an opportunity to mitigate image artifacts by an optimal trade-off between scan time, acceleration, and k-space sampling. Magn Reson Med 79:195-207, 2018. © 2018 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Emilie Bollache
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Alex J Barker
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Ryan Scott Dolan
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - James C Carr
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Pim van Ooij
- Department of Radiology, Academic Medical Center, Amsterdam, the Netherlands
| | - Rouzbeh Ahmadian
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Alex Powell
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Jeremy D Collins
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
| | - Julia Geiger
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.,Department of Diagnostic and Interventional Radiology, University Hospital of Würzburg, Würzburg, Germany
| | - Michael Markl
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA.,Department of Biomedical Engineering, McCormick School of Engineering, Northwestern University, Chicago, Illinois, USA
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Finn JP, Nguyen KL, Hu P. Ferumoxytol vs. Gadolinium agents for contrast-enhanced MRI: Thoughts on evolving indications, risks, and benefits. J Magn Reson Imaging 2017; 46:919-923. [PMID: 28160356 PMCID: PMC10156572 DOI: 10.1002/jmri.25580] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2016] [Accepted: 11/21/2016] [Indexed: 12/27/2022] Open
Affiliation(s)
- J Paul Finn
- Department of Radiological Sciences, UCLA, Los Angeles, California, USA.,Medicine, David Geffen School of Medicine, UCLA, Los Angeles, California, USA.,Department of Biomedical Physics, UCLA, Los Angeles, California, USA
| | - Kim-Lien Nguyen
- Medicine, David Geffen School of Medicine, UCLA, Los Angeles, California, USA
| | - Peng Hu
- Department of Radiological Sciences, UCLA, Los Angeles, California, USA.,Department of Biomedical Physics, UCLA, Los Angeles, California, USA
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Callaghan FM, Grieve SM. Spatial resolution and velocity field improvement of 4D-flow MRI. Magn Reson Med 2016; 78:1959-1968. [DOI: 10.1002/mrm.26557] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Revised: 09/27/2016] [Accepted: 10/28/2016] [Indexed: 11/10/2022]
Affiliation(s)
- Fraser M. Callaghan
- Sydney Translational Imaging Laboratory, Heart Research Institute, Charles Perkins Centre; University of Sydney; Sydney Australia
- Sydney Medical School; University of Sydney; Camperdown Australia
| | - Stuart M. Grieve
- Sydney Translational Imaging Laboratory, Heart Research Institute, Charles Perkins Centre; University of Sydney; Sydney Australia
- Sydney Medical School; University of Sydney; Camperdown Australia
- Department of Radiology; Royal Prince Alfred Hospital; Camperdown Australia
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Abstract
PURPOSE OF REVIEW Spurred by numerous recent technological advances, cardiac MRI (CMR) is now the gold standard for anatomic evaluation, quantitative assessment of chamber size and function, flow quantification, and tissue characterization. This review focuses on recent advances in pediatric and congenital CMR, highlighting recent safety data, and discussing future directions. RECENT FINDINGS CMR has become an important component of risk stratification and procedural planning in numerous congenital and pediatric heart diseases. Innovative approaches to image acquisition and reconstruction are leading the way toward fast, high-resolution, three- and four-dimensional datasets for delineation of cardiac anatomy, function, and flow. In addition, techniques for assessing the composition of the myocardium may help elucidate the pathophysiology of late complications, identify patients at risk for heart failure, and assist in the evaluation of therapeutic strategies. SUMMARY CMR provides invaluable morphologic, hemodynamic, and functional data that help guide diagnosis, assessment, and management of pediatric and adult congenital heart disease. As imaging techniques advance and data accumulate on the relative and additive value of CMR in patient care, its role in a multimodality approach to the care of this population of patients is becoming clear and is likely to continue to evolve.
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Lai LM, Cheng JY, Alley MT, Zhang T, Lustig M, Vasanawala SS. Feasibility of ferumoxytol-enhanced neonatal and young infant cardiac MRI without general anesthesia. J Magn Reson Imaging 2016; 45:1407-1418. [PMID: 27678106 DOI: 10.1002/jmri.25482] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Accepted: 09/01/2016] [Indexed: 01/28/2023] Open
Abstract
PURPOSE To assess the feasibility of ferumoxytol-enhanced anesthesia-free cardiac MRI in neonates and young infants for complex congenital heart disease (CHD). MATERIALS AND METHODS With Institutional Review Board approval, 21 consecutive neonates and young infants (1 day to 11 weeks old; median age of 3 days) who underwent a rapid two-sequence (MR angiography [MRA] and four-dimensional [4D] flow) MRI protocol with intravenous ferumoxytol without sedation (n = 17) or light sedation (n = 4) at 3 Tesla (T) (except one case at 1.5T) between June 2014 and February 2016 were retrospectively identified. Medical records were reviewed for indication, any complications, if further diagnostic imaging was performed after MRI, and surgical findings. Two radiologists scored the images in two sessions on a 5-point scale for overall image quality and delineation of various anatomical structures. Confidence interval of proportions for likelihood of requiring additional diagnostic imaging after MRI was determined. For the possibility of reducing the protocol to a single rapid sequence, Wilcoxon-rank sum test was used to assess whether 4D flow and MRA significantly differed in anatomical delineation. RESULTS One of 21 patients (4.8%, 80% confidence interval 0-11%) required additional imaging, a computed tomography angiography to assess lung parenchyma and peripheral pulmonary arteries. Only 1 of 13 patients (7.7%) with operative confirmation had a minor discrepancy between radiology and operative reports (80% confidence interval 0-17%). 4D flow was significantly superior to MRA (P < 0.05) for the evaluation of systemic arteries, valves, ventricular trabeculae, and overall quality. Using Cohen's kappa coefficient, there was good interobserver agreement for the evaluation of systemic arteries by 4D flow (κ = 0.782), and systemic veins and pulmonary arteries by MRA (κ > 0.6). Overall 4D flow measurements (mean κ = 0.64-0.74) had better internal agreement compared with MRA (mean κ = 0.30-0.64). CONCLUSION Ferumoxytol-enhanced cardiac MRI, without anesthesia, is feasible for the evaluation of complex CHD in neonates and young infants, with a low likelihood of need for additional diagnostic studies. The decreased risk by avoiding anesthesia must be balanced against the potential for adverse reactions with ferumoxytol. LEVEL OF EVIDENCE 2 J. MAGN. RESON. IMAGING 2017;45:1407-1418.
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Affiliation(s)
- Lillian M Lai
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Joseph Y Cheng
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Marcus T Alley
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Tao Zhang
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Michael Lustig
- Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, California, USA
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Han F, Zhou Z, Han E, Gao Y, Nguyen KL, Finn JP, Hu P. Self-gated 4D multiphase, steady-state imaging with contrast enhancement (MUSIC) using rotating cartesian K-space (ROCK): Validation in children with congenital heart disease. Magn Reson Med 2016; 78:472-483. [PMID: 27529745 DOI: 10.1002/mrm.26376] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Revised: 06/27/2016] [Accepted: 07/19/2016] [Indexed: 12/27/2022]
Abstract
PURPOSE To develop and validate a cardiac-respiratory self-gating strategy for the recently proposed multiphase steady-state imaging with contrast enhancement (MUSIC) technique. METHODS The proposed SG strategy uses the ROtating Cartesian K-space (ROCK) sampling, which allows for retrospective k-space binning based on motion surrogates derived from k-space center line. The k-space bins are reconstructed using a compressed sensing algorithm. Ten pediatric patients underwent cardiac MRI for clinical reasons. The original MUSIC and 2D-CINE images were acquired as a part of the clinical protocol, followed by the ROCK-MUSIC acquisition, all under steady-state intravascular distribution of ferumoxytol. Subjective scores and image sharpness were used to compare the images of ROCK-MUSIC and original MUSIC. RESULTS All scans were completed successfully without complications. The ROCK-MUSIC acquisition took 5 ± 1 min, compared to 8 ± 2 min for the original MUSIC. Image scores of ROCK-MUSIC were significantly better than original MUSIC at the ventricular outflow tracts (3.9 ± 0.3 vs. 3.3 ± 0.6, P < 0.05). There was a strong trend toward superior image scores for ROCK-MUSIC in the other anatomic locations. CONCLUSION ROCK-MUSIC provided images of equal or superior image quality compared to original MUSIC, and this was achievable with 40% savings in scan time and without the need for physiologic signal. Magn Reson Med 78:472-483, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Fei Han
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, California, USA.,Department of Bioengineering, University of California, Los Angeles, California, USA
| | - Ziwu Zhou
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, California, USA.,Department of Bioengineering, University of California, Los Angeles, California, USA
| | - Eric Han
- Harvard Westlake School, Los Angeles, California, USA
| | - Yu Gao
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, California, USA.,Biomedical Physics Inter-Departmental Graduate Program, University of California, Los Angeles, California, USA
| | - Kim-Lien Nguyen
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, California, USA.,Division of Cardiology, VA Greater Los Angeles Healthcare System, Los Angeles, California, USA
| | - J Paul Finn
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, California, USA
| | - Peng Hu
- Department of Radiological Sciences, David Geffen School of Medicine, University of California, Los Angeles, California, USA.,Biomedical Physics Inter-Departmental Graduate Program, University of California, Los Angeles, California, USA
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75
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Zhang T, Chen Y, Bao S, Alley MT, Pauly JM, Hargreaves BA, Vasanawala SS. Resolving phase ambiguity in dual-echo dixon imaging using a projected power method. Magn Reson Med 2016; 77:2066-2076. [PMID: 27221766 DOI: 10.1002/mrm.26287] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2016] [Revised: 05/03/2016] [Accepted: 05/04/2016] [Indexed: 12/11/2022]
Abstract
PURPOSE To develop a fast and robust method to resolve phase ambiguity in dual-echo Dixon imaging. METHODS A major challenge in dual-echo Dixon imaging is to estimate the phase error resulting from field inhomogeneity. In this work, a binary quadratic optimization program was formulated to resolve the phase ambiguity. A projected power method was developed to efficiently solve the optimization problem. Both the 1-peak fat model and 6-peak fat model were applied to three-dimensional (3D) datasets. Additionally, the proposed method was extended to dynamic magnetic resonance imaging (MRI) applications using the 6-peak fat model. With institutional review board (IRB) approval and patient consent/assent, the proposed method was evaluated and compared with region growing on 29 consecutive 3D high-resolution patient datasets. RESULTS Fast and robust water/fat separation was achieved by the proposed method in different representative 3D datasets and dynamic 3D datasets. Superior water/fat separation was achieved using the 6-peak fat model compared with the 1-peak fat model. Compared to region growing, the proposed method reduced water/fat swaps from 76 to 7% of the patient cohort. CONCLUSION The proposed method can achieve fast and robust phase error estimation in dual-echo Dixon imaging. Magn Reson Med 77:2066-2076, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
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Affiliation(s)
- Tao Zhang
- Department of Radiology, Stanford University, Stanford, California, USA.,Department of Electrical Engineering, Stanford University, Stanford, California, USA
| | - Yuxin Chen
- Department of Electrical Engineering, Princeton University, Princeton, New Jersey, USA
| | - Shanshan Bao
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Marcus T Alley
- Department of Radiology, Stanford University, Stanford, California, USA
| | - John M Pauly
- Department of Electrical Engineering, Stanford University, Stanford, California, USA
| | - Brian A Hargreaves
- Department of Radiology, Stanford University, Stanford, California, USA.,Department of Electrical Engineering, Stanford University, Stanford, California, USA
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Parekh K, Markl M, Rose M, Schnell S, Popescu A, Rigsby CK. 4D flow MR imaging of the portal venous system: a feasibility study in children. Eur Radiol 2016; 27:832-840. [PMID: 27193778 DOI: 10.1007/s00330-016-4396-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Revised: 03/28/2016] [Accepted: 05/02/2016] [Indexed: 12/26/2022]
Abstract
OBJECTIVES To determine the feasibility of 4D flow MRI for visualization and quantification of the portal venous haemodynamics in children and young adults. METHODS 4D flow was performed in 28 paediatric patients (median age, 8.5 years; interquartile range, 5.2-16.5), 15 with non-operated native portal system and 13 with surgically created portal shunt. Image quality assessment for 3D flow visualization and flow pattern analyses was performed. Regional 4D flow peak velocity and net flow were compared with 2D-cine phase contrast MRI (2D-PC MR) in the post-surgical patients. RESULTS Mean 3D flow visualization quality score was excellent (mean ± SD, 4.2 ± 0.9) with good inter-rater agreement (κ,0.67). Image quality in children aged >10 years was better than children ≤10 years (p < 0.05). Flow pattern was defined for portal, superior mesenteric, splenic veins and splenic artery in all patients. 4D flow and 2D-PC MR peak velocity and net flow were similar with good correlation (peak velocity: 4D flow 22.2 ± 9.1 cm/s and 2D-PC MR 25.2 ± 11.2 cm/s, p = 0.46; r = 0.92, p < 0.0001; net flow: 4D flow 9.5 ± 7.4 ml/s and 2D-PC MR 10.1 ± 7.3 ml/s, p = 0.65; r = 0.81, p = 0.0007). CONCLUSIONS 4D flow MRI is feasible and holds promise for the comprehensive 3D visualization and quantification of portal venous flow dynamics in children and young adults. KEY POINTS • 4D flow MRI is feasible in children and young adults. • 4D flow MRI has the ability to non-invasively characterize portal haemodynamics. • Image quality of 4D flow MRI is better is older children. • 4D flow MRI can accurately quantify portal flow compared to 2D-cine PC MRI.
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Affiliation(s)
- Keyur Parekh
- Department of Medical Imaging, Ann and Robert H. Lurie Children's Hospital of Chicago, 225 E. Chicago Ave., Chicago, IL, 60611, USA. .,Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.
| | - Michael Markl
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA.,Department of Biomedical Engineering, McCormick School of Engineering, Northwestern University, Chicago, IL, USA
| | - Michael Rose
- Department of Medical Imaging, Ann and Robert H. Lurie Children's Hospital of Chicago, 225 E. Chicago Ave., Chicago, IL, 60611, USA.,Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Susanne Schnell
- Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Andrada Popescu
- Department of Medical Imaging, Ann and Robert H. Lurie Children's Hospital of Chicago, 225 E. Chicago Ave., Chicago, IL, 60611, USA.,Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
| | - Cynthia K Rigsby
- Department of Medical Imaging, Ann and Robert H. Lurie Children's Hospital of Chicago, 225 E. Chicago Ave., Chicago, IL, 60611, USA.,Department of Radiology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA
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Hanneman K, Kino A, Cheng JY, Alley MT, Vasanawala SS. Assessment of the precision and reproducibility of ventricular volume, function, and mass measurements with ferumoxytol-enhanced 4D flow MRI. J Magn Reson Imaging 2016; 44:383-92. [PMID: 26871420 DOI: 10.1002/jmri.25180] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2015] [Accepted: 01/19/2016] [Indexed: 11/11/2022] Open
Abstract
PURPOSE To compare the precision and interobserver agreement of ventricular volume, function, and mass quantification by 3D time-resolved (4D) flow MRI relative to cine steady-state free precession (SSFP). MATERIALS AND METHODS With Institutional Research Board approval, informed consent, and HIPAA compliance, 22 consecutive patients with congenital heart disease (CHD) (10 males, 6.4 ± 4.8 years) referred for 3T ferumoxytol-enhanced cardiac MRI were prospectively recruited. Complete ventricular coverage with standard 2D short-axis cine SSFP and whole chest coverage with axial 4D flow were obtained. Two blinded radiologists independently segmented images for left ventricular (LV) and right ventricular (RV) myocardium at end systole (ES) and end diastole (ED). Statistical analysis included linear regression, analysis of variance (ANOVA), Bland-Altman (BA) analysis, and intraclass correlation (ICC). RESULTS Significant positive correlations were found between 4D flow and SSFP for ventricular volumes (r = 0.808-0.972, P < 0.001), ejection fraction (EF) (r = 0.900-928, P < 0.001), and mass (r = 0.884-0.934, P < 0.001). BA relative limits of agreement for both ventricles were between -52% to 34% for volumes, -29% to 27% for EF, and -41% to 48% for mass, with wider limits of agreement for the RV compared to the LV. There was no significant difference between techniques with respect to mean square difference of ED-ES mass for either LV (F = 2.05, P = 0.159) or RV (F = 0.625, P = 0.434). Interobserver agreement was moderate to good with both 4D flow (ICC 0.523-0.993) and SSFP (ICC 0.619-0.982), with overlapping confidence intervals. CONCLUSION Quantification of ventricular volume, function, and mass can be accomplished with 4D flow MRI with precision and interobserver agreement comparable to that of cine SSFP. J. Magn. Reson. Imaging 2016;44:383-392.
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Affiliation(s)
- Kate Hanneman
- Department of Radiology, Stanford University, Stanford, California, USA.,Department of Medical Imaging, Toronto General Hospital, University of Toronto, Toronto, Ontario, Canada
| | - Aya Kino
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Joseph Y Cheng
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Marcus T Alley
- Department of Radiology, Stanford University, Stanford, California, USA
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