1
|
Xanthis CG, Jablonowski R, Bidhult-Johansson S, Nordlund D, Haidich AB, Lala T, Arheden H, Aletras AH. Unravelling the mechanisms of CE-SSFP in imaging myocardium at risk: The effect of relaxation times on myocardial contrast. Magn Reson Imaging 2024; 111:90-102. [PMID: 38579972 DOI: 10.1016/j.mri.2024.03.043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 03/29/2024] [Accepted: 03/31/2024] [Indexed: 04/07/2024]
Abstract
PURPOSE The aim of this study was to investigate the contrast mechanisms of Contrast-enhanced steady-state free-precession (CE-SSFP) through the utilization of Bloch simulations in an experimental porcine model and in patients with acute myocardial infarction. METHODS Six pigs and ten patients with myocardial infarction underwent CMR and tissue characterization at 1.5 T whereas a Bloch simulation framework was utilized to simulate the CE-SSFP signal formation and compare it against the actual CE-SSFP signal acquired from the experimental porcine model and the patient population. The relaxation times of remote, salvaged, and infarcted myocardium were calculated after the injection of gadolinium, at the time of CE-SSFP acquisition. Simulations were performed using the same CE-SSFP pulse sequence as used on the scanner on a set of spins with the calculated relaxation times from the CMR scans. RESULTS The normalized signal intensities of salvaged and infarcted myocardium obtained with simulations were lower than the corresponding normalized signal intensities obtained in vivo in pigs (p < 0.05, 134% vs 153%) and in patients (p < 0.05, 126% vs 145%). The results from simulations showed a linear relationship to the results obtained in the experimental porcine model (r2 = 0.61) and in patients (r2 = 0.69). CONCLUSION The T1 and T2 values of remote, salvaged, and infarcted myocardium only partly explain the signal intensities in CE-SSFP images. Bloch simulations suggest that there may be more elements that contribute to the CE-SSFP contrast. Integration of other aspects of the MR experiment into the simulation model could further help to fully unravel the mechanisms of CE-SSFP.
Collapse
Affiliation(s)
- Christos G Xanthis
- Clinical Physiology, Department of Clinical Sciences Lund, Lund University, Skåne University Hospital, Lund, Sweden; Laboratory of Computing, Medical Informatics and Biomedical - Imaging Technologies, School of Medicine, Aristotle University of Thessaloniki, Thessaloniki, Greece
| | - Robert Jablonowski
- Clinical Physiology, Department of Clinical Sciences Lund, Lund University, Skåne University Hospital, Lund, Sweden
| | - Sebastian Bidhult-Johansson
- Clinical Physiology, Department of Clinical Sciences Lund, Lund University, Skåne University Hospital, Lund, Sweden
| | - David Nordlund
- Clinical Physiology, Department of Clinical Sciences Lund, Lund University, Skåne University Hospital, Lund, Sweden
| | - Anna-Bettina Haidich
- Laboratory of Hygiene, Social-Preventive Medicine and Medical Statistics, School of Medicine, Faculty of Health Sciences, Aristotle University of Thessaloniki, University Campus, 54124 Thessaloniki, Greece
| | - Tania Lala
- Clinical Physiology, Department of Clinical Sciences Lund, Lund University, Skåne University Hospital, Lund, Sweden; Department of Biomedical Engineering, Faculty of Engineering, Lund University, Lund, Sweden
| | - Håkan Arheden
- Clinical Physiology, Department of Clinical Sciences Lund, Lund University, Skåne University Hospital, Lund, Sweden
| | - Anthony H Aletras
- Clinical Physiology, Department of Clinical Sciences Lund, Lund University, Skåne University Hospital, Lund, Sweden; Laboratory of Computing, Medical Informatics and Biomedical - Imaging Technologies, School of Medicine, Aristotle University of Thessaloniki, Thessaloniki, Greece.
| |
Collapse
|
2
|
Yu A, Gao H, Ma Y, Li J, Zhang H. Feasibility study of the multishot gradient-echo planar imaging sequence in non-enhanced and free-breathing whole-heart magnetic resonance coronary angiography. Clin Radiol 2024; 79:e539-e545. [PMID: 38160106 DOI: 10.1016/j.crad.2023.12.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Revised: 11/22/2023] [Accepted: 12/12/2023] [Indexed: 01/03/2024]
Abstract
AIM To investigate the feasibility of non-enhanced and free-breathing whole-heart magnetic resonance coronary angiography (MRCA) using multishot gradient-echo planar imaging (MSG-EPI). MATERIALS AND METHODS In total, 29 healthy volunteers were recruited for free-breathing whole-heart MRCA acquisition using the MSG-EPI sequence and fast gradient echo (GRE) sequence. After the examination, the actual scanning times, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) of the left main (LM) coronary artery, subjective quality scores for each segment, and evaluable length of the coronary artery were recorded and statistically analysed. RESULTS There was no significant difference between the SNRLM of the MSG-EPI sequence and fast GRE sequence (p=0.130), but the CNRLM of the MSG-EPI sequence was higher (p=0.001). The subjective quality score of the mid- and distal left anterior descending branch as well as the distal circumflex branch of the coronary artery in the MSG-EPI sequence was higher than that in the fast GRE sequence (p=0.003, 0.001, and 0.003, respectively). The evaluable length of the left anterior descending branch and the circumflex branch was better using the MSG-EPI sequence than that of the fast GRE sequence (p=0.015 and < 0.001, respectively). Moreover, the scanning time of the MSG-EPI sequence was 54.5% less than that of the fast GRE sequence (p<0.001). CONCLUSION The MSG-EPI sequence improves the subjective and objective image quality of MRCA as well as reduces the scanning time.
Collapse
Affiliation(s)
- A Yu
- Department of Radiology, Tianjin Chest Hospital, Tianjin, China
| | - H Gao
- Department of Radiology, Tianjin Chest Hospital, Tianjin, China
| | - Y Ma
- Department of Radiology, Tianjin Chest Hospital, Tianjin, China
| | - J Li
- Department of Radiology, Tianjin Chest Hospital, Tianjin, China
| | - H Zhang
- Department of Radiology, Tianjin Chest Hospital, Tianjin, China.
| |
Collapse
|
3
|
Nurzed B, Kuehne A, Aigner CS, Schmitter S, Niendorf T, Eigentler TW. Radiofrequency antenna concepts for human cardiac MR at 14.0 T. MAGMA (NEW YORK, N.Y.) 2023; 36:257-277. [PMID: 36920549 PMCID: PMC10140016 DOI: 10.1007/s10334-023-01075-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Revised: 02/23/2023] [Accepted: 02/27/2023] [Indexed: 04/28/2023]
Abstract
OBJECTIVE To examine the feasibility of human cardiac MR (CMR) at 14.0 T using high-density radiofrequency (RF) dipole transceiver arrays in conjunction with static and dynamic parallel transmission (pTx). MATERIALS AND METHODS RF arrays comprised of self-grounded bow-tie (SGBT) antennas, bow-tie (BT) antennas, or fractionated dipole (FD) antennas were used in this simulation study. Static and dynamic pTx were applied to enhance transmission field (B1+) uniformity and efficiency in the heart of the human voxel model. B1+ distribution and maximum specific absorption rate averaged over 10 g tissue (SAR10g) were examined at 7.0 T and 14.0 T. RESULTS At 14.0 T static pTx revealed a minimum B1+ROI efficiency of 0.91 μT/√kW (SGBT), 0.73 μT/√kW (BT), and 0.56 μT/√kW (FD) and maximum SAR10g of 4.24 W/kg, 1.45 W/kg, and 2.04 W/kg. Dynamic pTx with 8 kT points indicate a balance between B1+ROI homogeneity (coefficient of variation < 14%) and efficiency (minimum B1+ROI > 1.11 µT/√kW) at 14.0 T with a maximum SAR10g < 5.25 W/kg. DISCUSSION MRI of the human heart at 14.0 T is feasible from an electrodynamic and theoretical standpoint, provided that multi-channel high-density antennas are arranged accordingly. These findings provide a technical foundation for further explorations into CMR at 14.0 T.
Collapse
Affiliation(s)
- Bilguun Nurzed
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin Ultrahigh Field Facility (B.U.F.F.), Robert Rössle Strasse 10, 13125, Berlin, Germany
| | | | | | | | - Thoralf Niendorf
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin Ultrahigh Field Facility (B.U.F.F.), Robert Rössle Strasse 10, 13125, Berlin, Germany.
- MRI.TOOLS GmbH, Berlin, Germany.
- Experimental and Clinical Research Center (ECRC), a joint cooperation between the Charité Medical Faculty and the Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association, Berlin, Germany.
| | - Thomas Wilhelm Eigentler
- Max-Delbrück-Center for Molecular Medicine in the Helmholtz Association (MDC), Berlin Ultrahigh Field Facility (B.U.F.F.), Robert Rössle Strasse 10, 13125, Berlin, Germany
- Chair of Medical Engineering, Technische Universität Berlin, Berlin, Germany
| |
Collapse
|
4
|
Terekhov M, Elabyad IA, Lohr D, Hofmann U, Schreiber LM. High-resolution imaging of the excised porcine heart at a whole-body 7 T MRI system using an 8Tx/16Rx pTx coil. MAGMA (NEW YORK, N.Y.) 2023; 36:279-293. [PMID: 37027119 PMCID: PMC10140105 DOI: 10.1007/s10334-023-01077-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2022] [Revised: 03/09/2023] [Accepted: 03/14/2023] [Indexed: 04/28/2023]
Abstract
INTRODUCTION MRI of excised hearts at ultra-high field strengths ([Formula: see text]≥7 T) can provide high-resolution, high-fidelity ground truth data for biomedical studies, imaging science, and artificial intelligence. In this study, we demonstrate the capabilities of a custom-built, multiple-element transceiver array customized for high-resolution imaging of excised hearts. METHOD A dedicated 16-element transceiver loop array was implemented for operation in parallel transmit (pTx) mode (8Tx/16Rx) of a clinical whole-body 7 T MRI system. The initial adjustment of the array was performed using full-wave 3D-electromagnetic simulation with subsequent final fine-tuning on the bench. RESULTS We report the results of testing the implemented array in tissue-mimicking liquid phantoms and excised porcine hearts. The array demonstrated high efficiency of parallel transmits characteristics enabling efficient pTX-based B1+-shimming. CONCLUSION The receive sensitivity and parallel imaging capability of the dedicated coil were superior to that of a commercial 1Tx/32Rx head coil in both SNR and T2*-mapping. The array was successfully tested to acquire ultra-high-resolution (0.1 × 0.1 × 0.8 mm voxel) images of post-infarction scar tissue. High-resolution (isotropic 1.6 mm3 voxel) diffusion tensor imaging-based tractography provided high-resolution information about normal myocardial fiber orientation.
Collapse
Affiliation(s)
- Maxim Terekhov
- Comprehensive Heart Failure Center (CHFC), Department of Cardiovascular Imaging, University Hospital Würzburg, Am Schwarzenberg 15, 97078, Würzburg, Germany.
| | - Ibrahim A Elabyad
- Comprehensive Heart Failure Center (CHFC), Department of Cardiovascular Imaging, University Hospital Würzburg, Am Schwarzenberg 15, 97078, Würzburg, Germany
| | - David Lohr
- Comprehensive Heart Failure Center (CHFC), Department of Cardiovascular Imaging, University Hospital Würzburg, Am Schwarzenberg 15, 97078, Würzburg, Germany
| | - Ulrich Hofmann
- Department of Internal Medicine I / Cardiology, University Hospital Würzburg, Oberdürrbacher Straße 6, 97080, Würzburg, Germany
| | - Laura M Schreiber
- Comprehensive Heart Failure Center (CHFC), Department of Cardiovascular Imaging, University Hospital Würzburg, Am Schwarzenberg 15, 97078, Würzburg, Germany
| |
Collapse
|
5
|
Guo R, Si D, Chen Z, Dai E, Chen S, Herzka DA, Luo J, Ding H. SAturation-recovery and Variable-flip-Angle-based three-dimensional free-breathing cardiovascular magnetic resonance T 1 mapping at 3 T. NMR IN BIOMEDICINE 2022; 35:e4755. [PMID: 35485432 DOI: 10.1002/nbm.4755] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2021] [Revised: 04/25/2022] [Accepted: 04/27/2022] [Indexed: 06/14/2023]
Abstract
The purpose of the current study was to develop and validate a three-dimensional (3D) free-breathing cardiac T1 -mapping sequence using SAturation-recovery and Variable-flip-Angle (SAVA). SAVA sequentially acquires multiple electrocardiogram-triggered volumes using a multishot spoiled gradient-echo sequence. The first volume samples the equilibrium signal of the longitudinal magnetization, where a flip angle of 2° is used to reduce the time for the magnetization to return to equilibrium. The succeeding three volumes are saturation prepared with variable delays, and are acquired using a 15° flip angle to maintain the signal-to-noise ratio. A diaphragmatic navigator is used to compensate the respiratory motion. T1 is calculated using a saturation-recovery model that accounts for the flip angle. We validated SAVA by simulations, phantom, and human subject experiments at 3 T. SAVA was compared with modified Look-Locker inversion recovery (MOLLI) and saturation-recovery single-shot acquisition (SASHA) in vivo. In phantoms, T1 by SAVA had good agreement with the reference (R2 = 0.99). In vivo 3D T1 mapping by SAVA could achieve an imaging resolution of 1.25 × 1.25 × 8 mm3 . Both global and septal T1 values by SAVA (1347 ± 37 and 1332 ± 42 ms) were in between those by SASHA (1612 ± 63 and 1618 ± 51 ms) and MOLLI (1143 ± 59 and 1188 ± 65 ms). According to the standard deviation (SD) and coefficient of variation (CV), T1 precision measured by SAVA (SD: 99 ± 14 and 60 ± 8 ms; CV: 7.4% ± 0.9% and 4.5% ± 0.6%) was comparable with MOLLI (SD: 99 ± 25 and 46 ± 12 ms; CV: 8.8% ± 2.5% and 3.9% ± 1.1%) and superior to SASHA (SD: 222 ± 89 and 132 ± 33 ms; CV: 13.8% ± 5.5% and 8.1% ± 2.0%). It was concluded that the proposed free-breathing SAVA sequence enables more efficient 3D whole-heart T1 estimation with good accuracy and precision.
Collapse
Affiliation(s)
- Rui Guo
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China
- School of Medical Technology, Beijing Institute of Technology, Beijing, China
| | - Dongyue Si
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China
| | - Zhensen Chen
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China
| | - Erpeng Dai
- Department of Radiology, Stanford University, Stanford, California, USA
| | - Shuo Chen
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China
| | - Daniel A Herzka
- National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, USA
| | - Jianwen Luo
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China
| | - Haiyan Ding
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China
| |
Collapse
|
6
|
Elabyad IA, Terekhov M, Lohr D, Bille M, Hock M, Schreiber LM. A novel antisymmetric 16-element transceiver dipole antenna array for parallel transmit cardiac MRI in pigs at 7 T. NMR IN BIOMEDICINE 2022; 35:e4726. [PMID: 35277907 DOI: 10.1002/nbm.4726] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Revised: 02/23/2022] [Accepted: 03/04/2022] [Indexed: 06/14/2023]
Abstract
To improve parallel transmit (pTx) and receive performance for cardiac MRI (cMRI) in pigs at 7 T, a dedicated transmit/receive (Tx/Rx), 16-element antisymmetric dipole antenna array, which combines L-shaped and straight dipoles, was designed, implemented, and evaluated in both cadavers and animals in vivo. Electromagnetic-field simulations were performed with the new 16-element dipole antenna array loaded with a pig thorax-shaped phantom and compared with an eight-element array of straight dipoles. The new dipole array was interfaced to a 7 T scanner in pTx mode (8Tx/16Rx). Imaging performance of the novel array was validated through MRI measurements in a pig phantom, an 85 kg pig cadaver, and two pigs in vivo (74 and 81 kg). Due to the improved decoupling between interleaved L-shaped and straight dipole elements, the 16-element dipole array fits within the same outer dimensions as an eight-element array of straight dipoles. This provides improvement of both transmit and receive characteristics and additional degrees of freedom for B1+ shimming. The antisymmetric dipole array demonstrated efficient suppression of destructive interferences in the B1+ field, with up to 25% improvement in the B1+ homogeneity achieved using static pTx-RFPA B1+ shimming in comparison with the hardware-adjusted state, which was optimized for single transmit. High-resolution (0.5 × 0.5 × 4 mm3 ) anatomical images of the heart after cardiac arrest proved good transmit and receive characteristics of the novel array design. Parallel imaging with an acceleration factor up to R = 6 was possible while maintaining a mean g factor of 1.55 within the pig heart. CINE images acquired in vivo in two pigs demonstrated SNR and parallel imaging capabilities similar to those of a reference 8Tx/16Rx dedicated loop array for cMRI in pigs.
Collapse
Affiliation(s)
- Ibrahim A Elabyad
- Comprehensive Heart Failure Center (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - Maxim Terekhov
- Comprehensive Heart Failure Center (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - David Lohr
- Comprehensive Heart Failure Center (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - Maya Bille
- Comprehensive Heart Failure Center (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - Michael Hock
- Comprehensive Heart Failure Center (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - Laura M Schreiber
- Comprehensive Heart Failure Center (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| |
Collapse
|
7
|
Herz S, Stefanescu MR, Lohr D, Vogel P, Kosmala A, Terekhov M, Weng AM, Grunz JP, Bley TA, Schreiber LM. Effects of image homogeneity on stenosis visualization at 7 T in a coronary artery phantom study: With and without B1-shimming and parallel transmission. PLoS One 2022; 17:e0270689. [PMID: 35767553 PMCID: PMC9242506 DOI: 10.1371/journal.pone.0270689] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2021] [Accepted: 06/15/2022] [Indexed: 11/18/2022] Open
Abstract
Background To investigate the effects of B1-shimming and radiofrequency (RF) parallel transmission (pTX) on the visualization and quantification of the degree of stenosis in a coronary artery phantom using 7 Tesla (7 T) magnetic resonance imaging (MRI). Methods Stenosis phantoms with different grades of stenosis (0%, 20%, 40%, 60%, 80%, and 100%; 5 mm inner vessel diameter) were produced using 3D printing (clear resin). Phantoms were imaged with four different concentrations of diluted Gd-DOTA representing established arterial concentrations after intravenous injection in humans. Samples were centrally positioned in a thorax phantom of 30 cm diameter filled with a custom-made liquid featuring dielectric properties of muscle tissue. MRI was performed on a 7 T whole-body system. 2D-gradient-echo sequences were acquired with an 8-channel transmit 16-channel receive (8 Tx / 16 Rx) cardiac array prototype coil with and without pTX mode. Measurements were compared to those obtained with identical scan parameters using a commercially available 1 Tx / 16 Rx single transmit coil (sTX). To assess reproducibility, measurements (n = 15) were repeated at different horizontal angles with respect to the B0-field. Results B1-shimming and pTX markedly improved flip angle homogeneity across the thorax phantom yielding a distinctly increased signal-to-noise ratio (SNR) averaged over a whole slice relative to non-manipulated RF fields. Images without B1-shimming showed shading artifacts due to local B1+-field inhomogeneities, which hampered stenosis quantification in severe cases. In contrast, B1-shimming and pTX provided superior image homogeneity. Compared with a conventional sTX coil higher grade stenoses (60% and 80%) were graded significantly (p<0.01) more precise. Mild to moderate grade stenoses did not show significant differences. Overall, SNR was distinctly higher with B1-shimming and pTX than with the conventional sTX coil (inside the stenosis phantoms 14%, outside the phantoms 32%). Both full and half concentration (10.2 mM and 5.1 mM) of a conventional Gd-DOTA dose for humans were equally suitable for stenosis evaluation in this phantom study. Conclusions B1-shimming and pTX at 7 T can distinctly improve image homogeneity and therefore provide considerably more accurate MR image analysis, which is beneficial for imaging of small vessel structures.
Collapse
Affiliation(s)
- Stefan Herz
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Würzburg, Würzburg, Germany
- Department of Diagnostic and Interventional Radiology, University Hospital Würzburg, Würzburg, Germany
- * E-mail:
| | - Maria R. Stefanescu
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Würzburg, Würzburg, Germany
| | - David Lohr
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Würzburg, Würzburg, Germany
| | - Patrick Vogel
- Department of Experimental Physics V, University of Würzburg, Würzburg, Germany
| | - Aleksander Kosmala
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Würzburg, Würzburg, Germany
- Department of Diagnostic and Interventional Radiology, University Hospital Würzburg, Würzburg, Germany
| | - Maxim Terekhov
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Würzburg, Würzburg, Germany
| | - Andreas M. Weng
- Department of Diagnostic and Interventional Radiology, University Hospital Würzburg, Würzburg, Germany
| | - Jan-Peter Grunz
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Würzburg, Würzburg, Germany
- Department of Diagnostic and Interventional Radiology, University Hospital Würzburg, Würzburg, Germany
| | - Thorsten A. Bley
- Department of Diagnostic and Interventional Radiology, University Hospital Würzburg, Würzburg, Germany
| | - Laura M. Schreiber
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Würzburg, Würzburg, Germany
| |
Collapse
|
8
|
Goerlich E, Schär M, Bagchi S, Soleimani-Fard A, Brown TT, Sarkar S, Bonanno G, Streeb V, Gerstenblith G, Barditch-Crovo P, Weiss RG, Hays AG. Coronary Endothelial Dysfunction in People Living With HIV Is Related to Body Fat Distribution. J Acquir Immune Defic Syndr 2022; 90:201-207. [PMID: 35131972 PMCID: PMC9203878 DOI: 10.1097/qai.0000000000002932] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 01/25/2022] [Indexed: 11/26/2022]
Abstract
BACKGROUND People living with HIV (PLWH) on antiretroviral therapy (ART) are at increased risk of atherosclerotic disease. Abnormal adipose distribution is common in PLWH and may contribute to atherosclerosis. Because coronary artery endothelial function (CEF) is impaired in early atherosclerosis, predicts future cardiovascular events, and is reduced in PLWH, we investigated associations between body fat distribution and CEF in PLWH. SETTING Prospective cohort study. METHODS PLWH on stable ART underwent MRI to quantify CEF, measured as change in coronary cross-sectional area from rest to that during isometric handgrip exercise, an endothelial-dependent stressor. Abdominal visceral and subcutaneous fat area (axial L4 level) and liver fat fraction were quantified using MRI. Linear regression was used to determine associations between CEF and independent variables. RESULTS Among 84 PLWH (52 ± 11 years; 33% women), mean cross-sectional area change was 0.74 ± 11.7%, indicating impaired CEF. On univariable regression analysis, CEF was inversely related to waist circumference (R = -0.31, P = 0.014), hip circumference (R = -0.27, P = 0.037), and subcutaneous fat area (R = -0.25, P = 0.031). We did not observe significant relationships between CEF and liver fat fraction, waist/hip ratio, or visceral fat area. On multivariable regression adjusted for age, sex, and race, CEF was associated with waist circumference, hip circumference, subcutaneous fat, and liver fat fraction. CONCLUSION Waist and hip circumference and subcutaneous fat area are associated with impaired CEF, an established metric of abnormal vascular health in PLWH on stable ART, and may contribute to the increased rate of heart disease in this population.
Collapse
Affiliation(s)
- Erin Goerlich
- Division of Cardiology, Johns Hopkins University, Baltimore, MD
| | - Michael Schär
- Department of Radiology, Johns Hopkins University, Baltimore, MD
| | - Shashwatee Bagchi
- Division of Infectious Disease and Institute of Human Virology, University of Maryland, Baltimore, MD; and
| | | | | | | | - Gabriele Bonanno
- Division of Cardiology, Johns Hopkins University, Baltimore, MD
- Department of Radiology, Johns Hopkins University, Baltimore, MD
| | - Valerie Streeb
- Division of Cardiology, Johns Hopkins University, Baltimore, MD
| | | | | | - Robert G Weiss
- Division of Cardiology, Johns Hopkins University, Baltimore, MD
- Department of Radiology, Johns Hopkins University, Baltimore, MD
| | - Allison G Hays
- Division of Cardiology, Johns Hopkins University, Baltimore, MD
- Department of Radiology, Johns Hopkins University, Baltimore, MD
| |
Collapse
|
9
|
Zhu D, Ding H, Zviman MM, Halperin H, Schär M, Herzka DA. Accelerating whole-heart 3D T2 mapping: Impact of undersampling strategies and reconstruction techniques. PLoS One 2021; 16:e0252777. [PMID: 34506496 PMCID: PMC8432823 DOI: 10.1371/journal.pone.0252777] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Accepted: 05/23/2021] [Indexed: 11/18/2022] Open
Abstract
PURPOSE We aim to determine an advantageous approach for the acceleration of high spatial resolution 3D cardiac T2 relaxometry data by comparing the performance of different undersampling patterns and reconstruction methods over a range of acceleration rates. METHODS Multi-volume 3D high-resolution cardiac images were acquired fully and undersampled retrospectively using 1) optimal CAIPIRINHA and 2) a variable density random (VDR) sampling. Data were reconstructed using 1) multi-volume sensitivity encoding (SENSE), 2) joint-sparsity SENSE and 3) model-based SENSE. Four metrics were calculated on 3 naïve swine and 8 normal human subjects over a whole left-ventricular region of interest: root-mean-square error (RMSE) of image signal intensity, RMSE of T2, the bias of mean T2, and standard deviation (SD) of T2. Fully sampled data and volume-by-volume SENSE with standard equally spaced undersampling were used as references. The Jaccard index calculated from one swine with acute myocardial infarction (MI) was used to demonstrate preservation of segmentation of edematous tissues with elevated T2. RESULTS In naïve swine and normal human subjects, all methods had similar performance when the net reduction factor (Rnet) <2.5. VDR sampling with model-based SENSE showed the lowest RMSEs (10.5%-14.2%) and SDs (+1.7-2.4 ms) of T2 when Rnet>2.5, while VDR sampling with the joint-sparsity SENSE had the lowest bias of mean T2 (0.0-1.1ms) when Rnet>3. The RMSEs of parametric T2 values (9.2%-24.6%) were larger than for image signal intensities (5.2%-18.4%). In the swine with MI, VDR sampling with either joint-sparsity or model-based SENSE showed consistently higher Jaccard index for all Rnet (0.71-0.50) than volume-by-volume SENSE (0.68-0.30). CONCLUSIONS Retrospective exploration of undersampling and reconstruction in 3D whole-heart T2 parametric mapping revealed that maps were more sensitive to undersampling than images, presenting a more stringent limiting factor on Rnet. The combination of VDR sampling patterns with model-based or joint-sparsity SENSE reconstructions were more robust for Rnet>3.
Collapse
Affiliation(s)
- Dan Zhu
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
- Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Haiyan Ding
- Department of Biomedical Engineering, Tsinghua University, Beijing, China
| | - M. Muz Zviman
- Department of Medicine, Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
- Department of Radiology, Perelman School of Medicine of The University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Henry Halperin
- Department of Medicine, Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Michael Schär
- Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
| | - Daniel A. Herzka
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America
- Laboratory of Cardiovascular Intervention, National Heart Lung and Blood Institute, NIH, Bethesda, Maryland, United States of America
- * E-mail:
| |
Collapse
|
10
|
Zhu D, Bonanno G, Hays AG, Weiss RG, Schär M. Phase contrast coronary blood velocity mapping with both high temporal and spatial resolution using triggered Golden Angle rotated Spiral k-t Sparse Parallel imaging (GASSP) with shifted binning. Magn Reson Med 2021; 86:1929-1943. [PMID: 33977581 DOI: 10.1002/mrm.28837] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2020] [Revised: 03/20/2021] [Accepted: 04/21/2021] [Indexed: 12/25/2022]
Abstract
PURPOSE High temporal and spatial resolutions are required for coronary blood flow measures. Current spiral breath-hold phase contrast (PC) MRI at 3T focus on either high spatial or high temporal resolution. We propose a golden angle (GA) rotated Spiral k-t Sparse Parallel imaging (GASSP) sequence for both high spatial (0.8 mm) and high temporal (<21 ms) resolutions. METHODS GASSP PC data are acquired in left anterior descending and right coronary arteries of eight healthy subjects. Binning of GA rotated spiral data into cardiac frames may lead to large k-space gaps. To reduce those gaps, the binning window is shifted and a triggered GA scheme that resets the rotation angle every heartbeat is proposed. The gap reductions are evaluated in simulations and all subjects. Peak systolic velocity (PSV), peak diastolic velocity (PDV), coronary blood flow rate, and vessel area are validated against two reference scans, and repeatability/reproducibility are determined. RESULTS Shifted binning reduced the mean k-space gaps of the triggered GA scheme by 14°-22° in simulations and about 20° in vivo. The k-space gap across three cardiac frames was reduced with the triggered GA scheme compared to the standard GA scheme (35.3°± 3.6° vs. 43°± 13.7°, t-test P = .04). PSV, PDV, flow rate, and area had high intra-scan repeatability (0.92 ≤ intraclass correlation coefficient [ICC] ≤ 0.99), and inter-scan (0.78 ≤ ICC ≤ 0.91) and intra-observer (0.91 ≤ ICC ≤ 0.98) reproducibility. CONCLUSION GASSP enables single breath-hold coronary PC MRI with high temporal and spatial resolutions. Shifted binning and a triggered GA scheme reduce k-space gaps. Quantitative coronary flow metrics are highly reproducible, especially within the same scanning session.
Collapse
Affiliation(s)
- Dan Zhu
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Gabriele Bonanno
- Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Department of Medicine, Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Allison G Hays
- Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Department of Medicine, Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Robert G Weiss
- Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.,Department of Medicine, Division of Cardiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Michael Schär
- Russell H. Morgan Department of Radiology and Radiological Science, Division of MR Research, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| |
Collapse
|
11
|
Goerlich E, Mukherjee M, Schar M, Brown TT, Bonanno G, Weiss RG, Hays AG. Noninvasive detection of impaired pulmonary artery endothelial function in people living with HIV. AIDS 2020; 34:2231-2238. [PMID: 32826392 DOI: 10.1097/qad.0000000000002671] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
OBJECTIVE People living with HIV (PLWH) have an increased risk of pulmonary vascular disease and pulmonary hypertension. Endothelial cell dysfunction is thought to contribute, but human studies have been limited by the invasive nature of conventional measures of pulmonary artery endothelial function (PAEF). We report here a noninvasive MRI approach to measure nitric oxide mediated PAEF by quantifying changes in pulmonary artery area and blood flow during isometric handgrip exercise (IHE), an endothelial nitric oxide dependent stressor. We used this to test the hypothesis that PLWH have impaired PAEF, even before development of pulmonary hypertension. DESIGN A prospective cohort study. METHODS We enrolled 25 HIV-positive viral-suppressed individuals on stable antiretroviral therapy without known or suspected pulmonary hypertension and 19 matched seronegative control individuals (HIV-negative). Pulmonary artery area and blood flow changes in response to IHE were measured with noncontrast MRI. Data previously collected during nitric oxide-synthase inhibition were analysed to determine the role of nitric oxide in the pulmonary artery response to IHE. RESULTS Seronegative individuals exhibited the anticipated PA vasodilatory response to IHE, but this was completely absent in HIV-positive individuals who exhibited an impaired area change (-1.1 ± 1.2 vs. +7.7 ± 2.2%, HIV-positive vs. HIV-negative, mean ± SEM, respectively, P = 0.002) and blood flow response (0.2 ± 2.3 vs. 13.5 ± 4.8%, P = 0.005). The pulmonary artery vasodilatory effect of IHE in healthy individuals was fully blocked by nitric oxide-synthase, demonstrating this pulmonary artery response is predominantly nitric oxide mediated. CONCLUSION Using noninvasive MRI methods to quantify PAEF, we observed significantly impaired PAEF in PLWH compared with matched HIV-negative controls. Noninvasive PAEF testing may be useful in evaluating early HIV-related pulmonary vascular disease.
Collapse
|
12
|
Schär M, Soleimanifard S, Bonanno G, Yerly J, Hays AG, Weiss RG. Precision and accuracy of cross-sectional area measurements used to measure coronary endothelial function with spiral MRI. Magn Reson Med 2019; 81:291-302. [PMID: 30024061 PMCID: PMC6258280 DOI: 10.1002/mrm.27384] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2018] [Revised: 04/25/2018] [Accepted: 05/09/2018] [Indexed: 01/22/2023]
Abstract
PURPOSE Coronary endothelial function (CEF) reflects vascular health and conventional invasive CEF measures predict cardiovascular events. MRI can now noninvasively measure CEF by quantifying coronary artery cross-sectional area changes in response to isometric handgrip exercise, an endothelial-dependent stressor. Area changes (10 to 20% in healthy; 2 to -12% in impaired vessels) are only a few imaging voxels because of MRI's limited spatial resolution. Here, with numerical simulations and phantom studies, we test whether Fourier interpolation enables sub-pixel area measurement precision and determine the smallest detectable area change using spiral MRI. METHODS In vivo coronary SNR with the currently used CEF protocol at 3T was measured in 7 subjects for subsequent in vitro work. Area measurements of circular vessels were simulated by varying partial volume, vessel diameter, voxel size, SNR, and Fourier interpolation factor. A phantom with precision-drilled holes (diameters 3-3.42 mm) was imaged 10 times with the current CEF protocol (voxel size, Δx = 0.89 mm) and a high-resolution protocol (Δx = 0.6 mm) to determine precision, accuracy, and the smallest detectable area changes. RESULTS In vivo coronary SNR ranged from 30-76. Eight-fold Fourier interpolation improved area measurement precision by a factor 6.5 and 4.9 in the simulations and phantom scans, respectively. The current CEF protocol can detect mean area changes of 4-5% for SNR above 30, and 3-3.5% for SNR above 40 with a higher-resolution protocol. CONCLUSION Current CEF spiral MRI with in vivo SNR allows detection of a 4-5% area change and Fourier interpolation improves precision several-fold to sub-voxel dimensions.
Collapse
Affiliation(s)
- Michael Schär
- Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Sahar Soleimanifard
- Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Gabriele Bonanno
- Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD, United States
- Division of Cardiology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Jérôme Yerly
- Department of Radiology, University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland
- Center for Biomedical Imaging (CIBM), Lausanne, Switzerland
| | - Allison G. Hays
- Division of Cardiology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, MD, United States
| | - Robert G. Weiss
- Russell H. Morgan Department of Radiology and Radiological Science, The Johns Hopkins University School of Medicine, Baltimore, MD, United States
- Division of Cardiology, Department of Medicine, The Johns Hopkins University School of Medicine, Baltimore, MD, United States
| |
Collapse
|
13
|
Rincón-Domínguez T, Menini A, Solana AB, Fischer A, Kudielka G, Haase A, Burschka D. Accelerated multi-snapshot free-breathing B1+ mapping based on the dual refocusing echo acquisition mode technique (DREAM): An alternative to measure RF nonuniformity for cardiac MRI. J Magn Reson Imaging 2018; 49:499-507. [DOI: 10.1002/jmri.26234] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2018] [Accepted: 06/06/2018] [Indexed: 12/28/2022] Open
Affiliation(s)
| | | | | | | | | | - Axel Haase
- Technische Universität München; Munich Germany
| | | |
Collapse
|
14
|
Guo R, Chen Z, Herzka DA, Luo J, Ding H. A three‐dimensional free‐breathing sequence for simultaneous myocardial T
1
and T
2
mapping. Magn Reson Med 2018; 81:1031-1043. [DOI: 10.1002/mrm.27466] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2018] [Revised: 06/13/2018] [Accepted: 07/03/2018] [Indexed: 12/26/2022]
Affiliation(s)
- Rui Guo
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine Tsinghua University Beijing China
| | - Zhensen Chen
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine Tsinghua University Beijing China
| | - Daniel A. Herzka
- Department of Biomedical Engineering Johns Hopkins School of Medicine Baltimore Maryland
- Cardiovascular Interventional Program, National Heart, Lung, and Blood Institute National Institutes of Health Bethesda Maryland
| | - Jianwen Luo
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine Tsinghua University Beijing China
| | - Haiyan Ding
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine Tsinghua University Beijing China
| |
Collapse
|
15
|
Guo R, Chen Z, Wang Y, Herzka DA, Luo J, Ding H. Three-dimensional free breathing whole heart cardiovascular magnetic resonance T 1 mapping at 3 T. J Cardiovasc Magn Reson 2018; 20:64. [PMID: 30220254 PMCID: PMC6139904 DOI: 10.1186/s12968-018-0487-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2018] [Accepted: 08/28/2018] [Indexed: 12/01/2022] Open
Abstract
BACKGROUND This study demonstrates a three-dimensional (3D) free-breathing native myocardial T1 mapping sequence at 3 T. METHODS The proposed sequence acquires three differently T1-weighted volumes. The first two volumes receive a saturation pre-pulse with different recovery time. The third volume is acquired without magnetization preparation and after a significant recovery time. Respiratory navigator gating and volume-interleaved acquisition are adopted to mitigate misregistration. The proposed sequence was validated through simulation, phantom experiments and in vivo experiments in 12 healthy adult subjects. RESULTS In phantoms, good agreement on T1 measurement was achieved between the proposed sequence and the reference inversion recovery spin echo sequence (R2 = 0.99). Homogeneous 3D T1 maps were obtained from healthy adult subjects, with a T1 value of 1476 ± 53 ms and a coefficient of variation (CV) of 6.1 ± 1.4% over the whole left-ventricular myocardium. The averaged septal T1 was 1512 ± 60 ms with a CV of 2.1 ± 0.5%. CONCLUSION Free-breathing 3D native T1 mapping at 3 T is feasible and may be applicable in myocardial assessment. The proposed 3D T1 mapping sequence is suitable for applications in which larger coverage is desired beyond that available with single-shot parametric mapping, or breath-holding is unfeasible.
Collapse
Affiliation(s)
- Rui Guo
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China
| | - Zhensen Chen
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China
| | - Yishi Wang
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China
| | - Daniel A. Herzka
- Department of Biomedical Engineering, Johns Hopkins School of Medicine, Baltimore, MD USA
- National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD USA
| | - Jianwen Luo
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China
| | - Haiyan Ding
- Center for Biomedical Imaging Research, Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China
| |
Collapse
|
16
|
Milford D, Rosbach N, Bendszus M, Heiland S. Mono-Exponential Fitting in T2-Relaxometry: Relevance of Offset and First Echo. PLoS One 2015; 10:e0145255. [PMID: 26678918 PMCID: PMC4683054 DOI: 10.1371/journal.pone.0145255] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Accepted: 11/30/2015] [Indexed: 11/18/2022] Open
Abstract
INTRODUCTION T2 relaxometry has become an important tool in quantitative MRI. Little focus has been put on the effect of the refocusing flip angle upon the offset parameter, which was introduced to account for a signal floor due to noise or to long T2 components. The aim of this study was to show that B1 imperfections contribute significantly to the offset. We further introduce a simple method to reduce the systematic error in T2 by discarding the first echo and using the offset fitting approach. MATERIALS AND METHODS Signal curves of T2 relaxometry were simulated based on extended phase graph theory and evaluated for 4 different methods (inclusion and exclusion of the first echo, while fitting with and without the offset). We further performed T2 relaxometry in a phantom at 9.4T magnetic resonance imaging scanner and used the same methods for post-processing as in the extended phase graph simulated data. Single spin echo sequences were used to determine the correct T2 time. RESULTS The simulation data showed that the systematic error in T2 and the offset depends on the refocusing pulse, the echo spacing and the echo train length. The systematic error could be reduced by discarding the first echo. Further reduction of the systematic T2 error was reached by using the offset as fitting parameter. The phantom experiments confirmed these findings. CONCLUSION The fitted offset parameter in T2 relaxometry is influenced by imperfect refocusing pulses. Using the offset as a fitting parameter and discarding the first echo is a fast and easy method to minimize the error in T2, particularly for low to intermediate echo train length.
Collapse
Affiliation(s)
- David Milford
- Department of Neuroradiology, University Hospital Heidelberg, Heidelberg, Germany
- * E-mail:
| | - Nicolas Rosbach
- Department of Neuroradiology, University Hospital Heidelberg, Heidelberg, Germany
| | - Martin Bendszus
- Department of Neuroradiology, University Hospital Heidelberg, Heidelberg, Germany
| | - Sabine Heiland
- Department of Neuroradiology, University Hospital Heidelberg, Heidelberg, Germany
| |
Collapse
|