1
|
Lohr D, Kollmann A, Bille M, Terekhov M, Elabyad I, Hock M, Baltes S, Reiter T, Schnitter F, Bauer WR, Hofmann U, Schreiber LM. Precision imaging of cardiac function and scar size in acute and chronic porcine myocardial infarction using ultrahigh-field MRI. COMMUNICATIONS MEDICINE 2024; 4:146. [PMID: 39026075 PMCID: PMC11258271 DOI: 10.1038/s43856-024-00559-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Accepted: 06/24/2024] [Indexed: 07/20/2024] Open
Abstract
BACKGROUND 7 T cardiac magnetic resonance imaging (MRI) studies may enable higher precision in clinical metrics like cardiac function, ventricular mass, and more. Higher precision may allow early detection of functional impairment and early evaluation of treatment responses in clinical practice and pre-clinical studies. METHODS Seven female German Landrace pigs were scanned prior to and at three time points (3-4 days, 7-10 days, and ~60 days) post myocardial infarction using a whole body 7 T system and three radiofrequency (RF) coils developed and built in-house to accompany animal growth. RESULTS The combination of dedicated RF hardware and 7 T MRI enables a longitudinal study in a pig model of acute and chronic infarction, providing consistent blood tissue contrast and high signal-to-noise ratio (SNR) in measurements of cardiac function, as well as low coefficients of variation (CoV) for ejection fraction (CoVintra-observer: 2%, CoVinter-observer: 3.8%) and infarct size (CoVintra-observer: 8.4%, CoVinter-observer: 3.8%), despite drastic animal growth. CONCLUSIONS Best results are achieved via manual segmentation. We define state-of-the-art procedures for large animal studies at 7 T.
Collapse
Affiliation(s)
- David Lohr
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Wuerzburg, Wuerzburg, Germany.
| | - Alena Kollmann
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Maya Bille
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Maxim Terekhov
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Ibrahim Elabyad
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Michael Hock
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Steffen Baltes
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Theresa Reiter
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Wuerzburg, Wuerzburg, Germany
- Department of Internal Medicine I, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Florian Schnitter
- Department of Internal Medicine I, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Wolfgang Rudolf Bauer
- Department of Internal Medicine I, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Ulrich Hofmann
- Department of Internal Medicine I, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Laura Maria Schreiber
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Wuerzburg, Wuerzburg, Germany.
| |
Collapse
|
2
|
Kollmann A, Lohr D, Ankenbrand MJ, Bille M, Terekhov M, Hock M, Elabyad I, Baltes S, Reiter T, Schnitter F, Bauer WR, Hofmann U, Schreiber LM. Cardiac function in a large animal model of myocardial infarction at 7 T: deep learning based automatic segmentation increases reproducibility. Sci Rep 2024; 14:11009. [PMID: 38744988 PMCID: PMC11094053 DOI: 10.1038/s41598-024-61417-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2023] [Accepted: 05/06/2024] [Indexed: 05/16/2024] Open
Abstract
Cardiac magnetic resonance (CMR) imaging allows precise non-invasive quantification of cardiac function. It requires reliable image segmentation for myocardial tissue. Clinically used software usually offers automatic approaches for this step. These are, however, designed for segmentation of human images obtained at clinical field strengths. They reach their limits when applied to preclinical data and ultrahigh field strength (such as CMR of pigs at 7 T). In our study, eleven animals (seven with myocardial infarction) underwent four CMR scans each. Short-axis cine stacks were acquired and used for functional cardiac analysis. End-systolic and end-diastolic images were labelled manually by two observers and inter- and intra-observer variability were assessed. Aiming to make the functional analysis faster and more reproducible, an established deep learning (DL) model for myocardial segmentation in humans was re-trained using our preclinical 7 T data (n = 772 images and labels). We then tested the model on n = 288 images. Excellent agreement in parameters of cardiac function was found between manual and DL segmentation: For ejection fraction (EF) we achieved a Pearson's r of 0.95, an Intraclass correlation coefficient (ICC) of 0.97, and a Coefficient of variability (CoV) of 6.6%. Dice scores were 0.88 for the left ventricle and 0.84 for the myocardium.
Collapse
Affiliation(s)
- Alena Kollmann
- 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.
| | - Markus J Ankenbrand
- Faculty of Biology, Center for Computational and Theoretical Biology (CCTB), University of Würzburg, Würzburg, Germany
| | - Maya Bille
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Würzburg, Würzburg, Germany
| | - Maxim Terekhov
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Würzburg, Würzburg, Germany
| | - Michael Hock
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Würzburg, Würzburg, Germany
| | - Ibrahim Elabyad
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Würzburg, Würzburg, Germany
| | - Steffen Baltes
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Würzburg, Würzburg, Germany
| | - Theresa Reiter
- Comprehensive Heart Failure Center (CHFC), Chair of Molecular and Cellular Imaging, University Hospital Würzburg, Würzburg, Germany
- Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
| | - Florian Schnitter
- Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
| | - Wolfgang R Bauer
- Department of Internal Medicine I, University Hospital Würzburg, Würzburg, Germany
| | - Ulrich Hofmann
- Department of Internal Medicine I, 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
|
3
|
Schreiber LM, Lohr D, Baltes S, Vogel U, Elabyad IA, Bille M, Reiter T, Kosmala A, Gassenmaier T, Stefanescu MR, Kollmann A, Aures J, Schnitter F, Pali M, Ueda Y, Williams T, Christa M, Hofmann U, Bauer W, Gerull B, Zernecke A, Ergün S, Terekhov M. Ultra-high field cardiac MRI in large animals and humans for translational cardiovascular research. Front Cardiovasc Med 2023; 10:1068390. [PMID: 37255709 PMCID: PMC10225557 DOI: 10.3389/fcvm.2023.1068390] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Accepted: 04/04/2023] [Indexed: 06/01/2023] Open
Abstract
A key step in translational cardiovascular research is the use of large animal models to better understand normal and abnormal physiology, to test drugs or interventions, or to perform studies which would be considered unethical in human subjects. Ultrahigh field magnetic resonance imaging (UHF-MRI) at 7 T field strength is becoming increasingly available for imaging of the heart and, when compared to clinically established field strengths, promises better image quality and image information content, more precise functional analysis, potentially new image contrasts, and as all in-vivo imaging techniques, a reduction of the number of animals per study because of the possibility to scan every animal repeatedly. We present here a solution to the dual use problem of whole-body UHF-MRI systems, which are typically installed in clinical environments, to both UHF-MRI in large animals and humans. Moreover, we provide evidence that in such a research infrastructure UHF-MRI, and ideally combined with a standard small-bore UHF-MRI system, can contribute to a variety of spatial scales in translational cardiovascular research: from cardiac organoids, Zebra fish and rodent hearts to large animal models such as pigs and humans. We present pilot data from serial CINE, late gadolinium enhancement, and susceptibility weighted UHF-MRI in a myocardial infarction model over eight weeks. In 14 pigs which were delivered from a breeding facility in a national SARS-CoV-2 hotspot, we found no infection in the incoming pigs. Human scanning using CINE and phase contrast flow measurements provided good image quality of the left and right ventricle. Agreement of functional analysis between CINE and phase contrast MRI was excellent. MRI in arrested hearts or excised vascular tissue for MRI-based histologic imaging, structural imaging of myofiber and vascular smooth muscle cell architecture using high-resolution diffusion tensor imaging, and UHF-MRI for monitoring free radicals as a surrogate for MRI of reactive oxygen species in studies of oxidative stress are demonstrated. We conclude that UHF-MRI has the potential to become an important precision imaging modality in translational cardiovascular research.
Collapse
Affiliation(s)
- Laura M. Schreiber
- Department of Cardiovascular Imaging and Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center Wuerzburg (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - David Lohr
- Department of Cardiovascular Imaging and Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center Wuerzburg (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - Steffen Baltes
- Department of Cardiovascular Imaging and Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center Wuerzburg (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - Ulrich Vogel
- Institute for Hygiene and Microbiology, University of Wuerzburg, Wuerzburg, Germany
| | - Ibrahim A. Elabyad
- Department of Cardiovascular Imaging and Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center Wuerzburg (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - Maya Bille
- Department of Cardiovascular Imaging and Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center Wuerzburg (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - Theresa Reiter
- Department of Cardiovascular Imaging and Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center Wuerzburg (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
- Department of Internal Medicine I/Cardiology, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Aleksander Kosmala
- Department of Cardiovascular Imaging and Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center Wuerzburg (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
- Department of Radiology, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Tobias Gassenmaier
- Department of Cardiovascular Imaging and Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center Wuerzburg (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
- Department of Radiology, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Maria R. Stefanescu
- Department of Cardiovascular Imaging and Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center Wuerzburg (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - Alena Kollmann
- Department of Cardiovascular Imaging and Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center Wuerzburg (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - Julia Aures
- Department of Cardiovascular Imaging and Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center Wuerzburg (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - Florian Schnitter
- Department of Internal Medicine I/Cardiology, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Mihaela Pali
- Department of Cardiovascular Imaging and Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center Wuerzburg (CHFC), University Hospital Wuerzburg, Wuerzburg, Germany
| | - Yuichiro Ueda
- Institute of Anatomy and Cell Biology, Julius-Maximilians-University, Wuerzburg, Germany
| | - Tatiana Williams
- Department of Cardiovascular Genetics, Comprehensive Heart Failure Center Wuerzburg, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Martin Christa
- Department of Internal Medicine I/Cardiology, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Ulrich Hofmann
- Department of Internal Medicine I/Cardiology, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Wolfgang Bauer
- Department of Internal Medicine I/Cardiology, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Brenda Gerull
- Department of Internal Medicine I/Cardiology, University Hospital Wuerzburg, Wuerzburg, Germany
- Department of Cardiovascular Genetics, Comprehensive Heart Failure Center Wuerzburg, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Alma Zernecke
- Institute of Experimental Biomedicine, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Süleyman Ergün
- Institute of Anatomy and Cell Biology, Julius-Maximilians-University, Wuerzburg, Germany
| | - Maxim Terekhov
- Department of Cardiovascular Imaging and Chair of Molecular and Cellular Imaging, Comprehensive Heart Failure Center Wuerzburg (CHFC), University Hospital Wuerzburg, Wuerzburg, 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
|
Williams SN, McElhinney P, Gunamony S. Ultra-high field MRI: parallel-transmit arrays and RF pulse design. Phys Med Biol 2023; 68. [PMID: 36410046 DOI: 10.1088/1361-6560/aca4b7] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2022] [Accepted: 11/21/2022] [Indexed: 11/22/2022]
Abstract
This paper reviews the field of multiple or parallel radiofrequency (RF) transmission for magnetic resonance imaging (MRI). Currently the use of ultra-high field (UHF) MRI at 7 tesla and above is gaining popularity, yet faces challenges with non-uniformity of the RF field and higher RF power deposition. Since its introduction in the early 2000s, parallel transmission (pTx) has been recognized as a powerful tool for accelerating spatially selective RF pulses and combating the challenges associated with RF inhomogeneity at UHF. We provide a survey of the types of dedicated RF coils used commonly for pTx and the important modeling of the coil behavior by electromagnetic (EM) field simulations. We also discuss the additional safety considerations involved with pTx such as the specific absorption rate (SAR) and how to manage them. We then describe the application of pTx with RF pulse design, including a practical guide to popular methods. Finally, we conclude with a description of the current and future prospects for pTx, particularly its potential for routine clinical use.
Collapse
Affiliation(s)
- Sydney N Williams
- Imaging Centre of Excellence, University of Glasgow, Glasgow, United Kingdom
| | - Paul McElhinney
- Imaging Centre of Excellence, University of Glasgow, Glasgow, United Kingdom
| | - Shajan Gunamony
- Imaging Centre of Excellence, University of Glasgow, Glasgow, United Kingdom.,MR CoilTech Limited, Glasgow, United Kingdom
| |
Collapse
|
6
|
Gokyar S, Voss HU, Taracila V, Robb FJL, Bernico M, Kelley D, Ballon DJ, Winkler SA. A pathway towards a two-dimensional, bore-mounted, volume body coil concept for ultra high-field magnetic resonance imaging. NMR IN BIOMEDICINE 2022; 35:e4802. [PMID: 35834176 DOI: 10.1002/nbm.4802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 07/08/2022] [Accepted: 07/12/2022] [Indexed: 06/15/2023]
Abstract
Lack of a body-sized, bore-mounted, radiofrequency (RF) body coil for ultrahigh field (UHF) magnetic resonance imaging (MRI) is one of the major drawbacks of UHF, hampering the clinical potential of the technology. Transmit field (B1 ) nonuniformity and low specific absorption rate (SAR) efficiencies in UHF MRI are two challenges to be overcome. To address these problems, and ultimately provide a pathway for the full clinical potential of the modality, we have designed and simulated two-dimensional cylindrical high-pass ladder (2D c-HPL) architectures for clinical bore-size dimensions, and demonstrated a simplified proof of concept with a head-sized prototype at 7 T. A new dispersion relation has been derived and electromagnetic simulations were used to verify coil modes. The coefficient of variation (CV) for brain, cerebellum, heart, and prostate tissues after B1 + shimming in silico is reported and compared with previous works. Three prototypes were designed in simulation: a head-sized, body-sized, and long body-sized coil. The head-sized coil showed a CV of 12.3%, a B1 + efficiency of 1.33 μT/√W, and a SAR efficiency of 2.14 μT/√(W/kg) for brain simulations. The body-sized 2D c-HPL coil was compared with same-sized transverse electromagnetic (TEM) and birdcage coils in silico with a four-port circularly polarized mode excitation. Improved B1 + uniformity (26.9%) and SAR efficiency (16% and 50% better than birdcage and TEM coils, respectively) in spherical phantoms was observed. We achieved a CV of 12.3%, 4.9%, 16.7%, and 2.8% for the brain, cerebellum, heart, and prostate, respectively. Preliminary imaging results for the head-sized coil show good agreement between simulation and experiment. Extending the 1D birdcage coil concept to 2D c-HPLs provides improved B1 + uniformity and SAR efficiency.
Collapse
Affiliation(s)
- Sayim Gokyar
- Department of Radiology, Weill Cornell Medicine, New York, New York, USA
- USC Mark and Mary Stevens Neuroimaging and Informatics Institute, Los Angeles, California, USA
| | - Henning U Voss
- College of Human Ecology, Cornell University, Ithaca, New York, USA
| | | | | | | | | | - Douglas J Ballon
- Department of Radiology, Weill Cornell Medicine, New York, New York, USA
| | | |
Collapse
|
7
|
In Vivo Magnetic Resonance Spectroscopy Methods for Investigating Cardiac Metabolism. Metabolites 2022; 12:metabo12020189. [PMID: 35208262 PMCID: PMC8877606 DOI: 10.3390/metabo12020189] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2021] [Revised: 02/14/2022] [Accepted: 02/15/2022] [Indexed: 11/17/2022] Open
Abstract
Magnetic resonance spectroscopy (MRS) is a non-invasive and non-ionizing technique, enabling in vivo investigation of cardiac metabolism in normal and diseased hearts. In vivo measurement tools are critical for studying mechanisms that regulate cardiac energy metabolism in disease developments and to assist in early response assessments to novel therapies. For cardiac MRS, proton (1H), phosphorus (31P), and hyperpolarized 13-carbon (13C) provide valuable metabolic information for diagnosis and treatment assessment purposes. Currently, low sensitivity and some technical limitations limit the utility of MRS. An essential step in translating MRS for clinical use involves further technological improvements, particularly in coil design, improving the signal-to-noise ratios, field homogeneity, and optimizing radiofrequency sequences. This review addresses the recent advances in metabolic imaging by MRS from primarily the literature published since 2015.
Collapse
|
8
|
Terekhov M, Elabyad IA, Schreiber LM. Global optimization of default phases for parallel transmit coils for ultra-high-field cardiac MRI. PLoS One 2021; 16:e0255341. [PMID: 34358243 PMCID: PMC8346258 DOI: 10.1371/journal.pone.0255341] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Accepted: 07/14/2021] [Indexed: 11/19/2022] Open
Abstract
The development of novel multiple-element transmit-receive arrays is an essential factor for improving B1+ field homogeneity in cardiac MRI at ultra-high magnetic field strength (B0 > = 7.0T). One of the key steps in the design and fine-tuning of such arrays during the development process is finding the default driving phases for individual coil elements providing the best possible homogeneity of the combined B1+-field that is achievable without (or before) subject-specific B1+-adjustment in the scanner. This task is often solved by time-consuming (brute-force) or by limited efficiency optimization methods. In this work, we propose a robust technique to find phase vectors providing optimization of the B1-homogeneity in the default setup of multiple-element transceiver arrays. The key point of the described method is the pre-selection of starting vectors for the iterative solver-based search to maximize the probability of finding a global extremum for a cost function optimizing the homogeneity of a shaped B1+-field. This strategy allows for (i) drastic reduction of the computation time in comparison to a brute-force method and (ii) finding phase vectors providing a combined B1+-field with homogeneity characteristics superior to the one provided by the random-multi-start optimization approach. The method was efficiently used for optimizing the default phase settings in the in-house-built 8Tx/16Rx arrays designed for cMRI in pigs at 7T.
Collapse
Affiliation(s)
- Maxim Terekhov
- Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Center, University Hospital Wuerzburg, Wuerzburg, Germany
- * E-mail:
| | - Ibrahim A. Elabyad
- Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Center, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Laura M. Schreiber
- Chair of Cellular and Molecular Imaging, Comprehensive Heart Failure Center, University Hospital Wuerzburg, Wuerzburg, Germany
| |
Collapse
|
9
|
Reiter T, Lohr D, Hock M, Ankenbrand MJ, Stefanescu MR, Kosmala A, Kaspar M, Juchem C, Terekhov M, Schreiber LM. On the way to routine cardiac MRI at 7 Tesla - a pilot study on consecutive 84 examinations. PLoS One 2021; 16:e0252797. [PMID: 34297720 PMCID: PMC8301632 DOI: 10.1371/journal.pone.0252797] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2020] [Accepted: 05/23/2021] [Indexed: 11/29/2022] Open
Abstract
INTRODUCTION Cardiac magnetic resonance (CMR) at ultrahigh field (UHF) offers the potential of high resolution and fast image acquisition. Both technical and physiological challenges associated with CMR at 7T require specific hardware and pulse sequences. This study aimed to assess the current status and existing, publicly available technology regarding the potential of a clinical application of 7T CMR. METHODS Using a 7T MRI scanner and a commercially available radiofrequency coil, a total of 84 CMR examinations on 72 healthy volunteers (32 males, age 19-70 years, weight 50-103 kg) were obtained. Both electrocardiographic and acoustic triggering were employed. The data were analyzed regarding the diagnostic image quality and the influence of patient and hardware dependent factors. 50 complete short axis stacks and 35 four chamber CINE views were used for left ventricular (LV) and right ventricular (RV), mono-planar LV function, and RV fractional area change (FAC). Twenty-seven data sets included aortic flow measurements that were used to calculate stroke volumes. Subjective acceptance was obtained from all volunteers with a standardized questionnaire. RESULTS Functional analysis showed good functions of LV (mean EF 56%), RV (mean EF 59%) and RV FAC (mean FAC 52%). Flow measurements showed congruent results with both ECG and ACT triggering. No significant influence of experimental parameters on the image quality of the LV was detected. Small fractions of 5.4% of LV and 2.5% of RV segments showed a non-diagnostic image quality. The nominal flip angle significantly influenced the RV image quality. CONCLUSION The results demonstrate that already now a commercially available 7T MRI system, without major methods developments, allows for a solid morphological and functional analysis similar to the clinically established CMR routine approach. This opens the door towards combing routine CMR in patients with development of advanced 7T technology.
Collapse
Affiliation(s)
- Theresa Reiter
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
- Department of Internal Medicine I, Cardiology, University Hospital Wuerzburg, Wuerzburg, Germany
| | - David Lohr
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Michael Hock
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Markus Johannes Ankenbrand
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Maria Roxana Stefanescu
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Aleksander Kosmala
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
- Department of Radiology, University Hospital Wuerzburg, Wuerzburg, Germany
| | - Mathias Kaspar
- Department of Health Services Research, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Christoph Juchem
- Departments of Biomedical Engineering and Radiology, Columbia University, New York, New York, United States of America
| | - Maxim Terekhov
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| | - Laura Maria Schreiber
- Comprehensive Heart Failure Center Wuerzburg (CHFC), Chair of Molecular and Cellular Imaging, Wuerzburg, Germany
| |
Collapse
|
10
|
Beck MJ, Parker DL, Hadley JR. Capacitive versus Overlap Decoupling of Adjacent Radio Frequency Phased Array Coil Elements: An Imaging Robustness Comparison When Sample Load Varies for 3 Tesla MRI. CONCEPTS IN MAGNETIC RESONANCE. PART B, MAGNETIC RESONANCE ENGINEERING 2020; 2020:8828047. [PMID: 34867110 PMCID: PMC8640609 DOI: 10.1155/2020/8828047] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Phased array (PA) receive coils are built such that coil elements approximate independent antenna behavior. One method of achieving this goal is to use an available decoupling method to decouple adjacent coil elements. The purpose of this work was to compare the relative performance of two decoupling methods as a function of variation in sample load. Two PA receive coils with 5 channels (5-ch) each, equal outer dimensions, and formed on 12 cm diameter cylindrical phantoms of conductivities 0.3, 0.6, and 0.9 S/m were evaluated for relative signal-to-noise ratio (SNR) and parallel imaging performance. They were only tuned and matched to the 0.6 S/m phantom. Simulated and measured axial, sagittal, and coronal 5-ch PA coil SNR ratios were compared by dividing the overlap by the capacitive decoupled coil SNR results. Issues related to the selection of capacitor values for the two decoupling methods were evaluated by taking the ratio of the match and tune capacitors for large and small 2 channel (2-ch) PA coils. The SNR ratios showed that the SNR of the two decoupling methods were very similar. The inverse geometry-factor maps showed similar but better overall parallel imaging performance for the capacitive decoupled method. The quotients for the 2-ch PA coils' maximum and minimum capacitor value ratios are 3.28 and 1.38 for the large and 3.28 and 2.22 for the small PA. The results of this paper demonstrate that as the sample load varies, the capacitive and overlap decoupling methods are very similar in relative SNR and this similarity continues for parallel imaging performance. Although, for the 5-ch coils studied, the capacitive decoupling method has a slight SNR and parallel imaging advantage and it was noted that the capacitive decoupled coil is more likely to encounter unbuildable PA coil configurations.
Collapse
Affiliation(s)
- Michael J Beck
- Department of Radiology and Imaging Sciences, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City 84132, USA
| | - Dennis L Parker
- Department of Radiology and Imaging Sciences, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City 84132, USA
| | - J Rock Hadley
- Department of Radiology and Imaging Sciences, Utah Center for Advanced Imaging Research, University of Utah, Salt Lake City 84132, USA
| |
Collapse
|