High Field Cardiac Magnetic Resonance Imaging: A Case for Ultrahigh Field Cardiac Magnetic Resonance

Precision imaging of cardiac function and scar size in acute and chronic porcine myocardial infarction using ultrahigh-field MRI

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.

Clinical impact of novel CMR technology on patients with congenital heart disease. A scientific statement of the Association for European Pediatric and Congenital Cardiology (AEPC) and the European Association of Cardiovascular Imaging (EACVI) of the ESC

Cardiovascular magnetic resonance (CMR) imaging is recommended in patients with congenital heart disease (CHD) in clinical practice guidelines as the imaging standard for a large variety of diseases. As CMR is evolving, novel techniques are becoming available. Some of them are already used clinically, whereas others still need further evaluation. In this statement the authors give an overview of relevant new CMR techniques for the assessment of CHD. Studies with reference values for these new techniques are listed in the supplement.

Improved 1 H body imaging at 10.5 T: Validation and VOP-enabled imaging in vivo with a 16-channel transceiver dipole array

PURPOSE

To increase the RF coil performance and RF management for body imaging at 10.5 T by validating and evaluating a high-density 16-channel transceiver array, implementing virtual observation points (VOPs), and demonstrating specific absorption rate (SAR) constrained imaging in vivo.

METHODS

The inaccuracy of the electromagnetic model of the array was quantified based on B1 + and SAR data. Inter-subject variability was estimated using a new approach based on the relative SAR deviation of different RF shims between human body models. The pTx performance of the 16-channel array was assessed in simulation by comparison to a previously demonstrated 10-channel array. In vivo imaging of the prostate was performed demonstrating SAR-constrained static RF shimming and acquisition modes optimized for refocused echoes (AMORE).

RESULTS

The model inaccuracy of 29% and the inter-subject variability of 85% resulted in a total safety factor of 1.91 for pelvis studies. For renal and cardiac imaging, inter-subject variabilities of 121% and 141% lead to total safety factors of 2.25 and 2.45, respectively. The shorter wavelength at 10.5 T supported the increased element density of the 16-channel array which in turn outperformed the 10-channel version for all investigated metrics. Peak 10 g local SAR reduction of more than 25% without a loss of image quality was achieved in vivo, allowing a theoretical improvement in measurement efficiency of up to 66%.

CONCLUSIONS

By validating and characterizing a 16-channel dipole transceiver array, this work demonstrates, for the first time, a VOP-enabled RF coil for human torso imaging enabling increased pTx performance at 10.5 T.

Cardiothoracic and Vascular Surgery Implant Compatibility With Ultrahigh Field Magnetic Resonance Imaging (4.7 Tesla and 7 Tesla)

The use of 7 Tesla (T) magnetic resonance imaging (MRI) is expanding across medical specialties, particularly, clinical neurosciences and orthopedics. Investigational 7 T MRI has also been performed in cardiology. A limiting factor for expansion of the role of 7 T, irrespective of the body part being imaged, is the sparse testing of biomedical implant compatibility at field strengths >3 T. Implant compatibility can be tested following the American Society for Testing and Materials International guidelines. To assess the current state of cardiovascular implant safety at field strengths >3 T, a systematic search was performed using PubMed, Web of Science, and citation matching. Studies written in English that included at least 1 cardiovascular-related implant and at least 1 safety outcome (deflection angle, torque, or temperature change) were included. Data were extracted for the implant studied, implant composition, deflection angle, torque, and temperature change, and the American Society for Testing and Materials International standards were followed. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses reporting guidelines for scoping reviews were followed. A total of 9 studies were included. A total of 34 cardiovascular-related implants tested ex vivo at 7 T and 91 implants tested ex vivo at 4.7 T were included. The implants included vascular grafts and conduits, vascular access ports, peripheral and coronary stents, caval filters, and artificial valves. A total of 2 grafts, 1 vascular access port, 2 vena cava filters, and 5 stents were identified as incompatible with the 7 T MRI. All incompatible stents were 40 mm in length. Based on the safety outcomes reported, we identify several implants that may be compatible with >3 T MRI. This scoping review seeks to concisely summarize all the cardiovascular-related implants tested for ultrahigh field MRI compatibility to date.

Ultra-high field cardiac MRI in large animals and humans for translational cardiovascular research

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.

Radiofrequency antenna concepts for human cardiac MR at 14.0 T

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 (SAR_10g) 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 SAR_10g 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 SAR_10g < 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.

High-resolution imaging of the excised porcine heart at a whole-body 7 T MRI system using an 8Tx/16Rx pTx coil

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.

Effects of image homogeneity on stenosis visualization at 7 T in a coronary artery phantom study: With and without B1-shimming and parallel transmission

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.

Sustainable low-field cardiovascular magnetic resonance in changing healthcare systems

Cardiovascular disease continues to be a major burden facing healthcare systems worldwide. In the developed world, cardiovascular magnetic resonance (CMR) is a well-established non-invasive imaging modality in the diagnosis of cardiovascular disease. However, there is significant global inequality in availability and access to CMR due to its high cost, technical demands as well as existing disparities in healthcare and technical infrastructures across high-income and low-income countries. Recent renewed interest in low-field CMR has been spurred by the clinical need to provide sustainable imaging technology capable of yielding diagnosticquality images whilst also being tailored to the local populations and healthcare ecosystems. This review aims to evaluate the technical, practical and cost considerations of low field CMR whilst also exploring the key barriers to implementing sustainable MRI in both the developing and developed world.

In Vivo Magnetic Resonance Spectroscopy Methods for Investigating Cardiac Metabolism

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.

Global optimization of default phases for parallel transmit coils for ultra-high-field cardiac MRI

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.

32-Channel self-grounded bow-tie transceiver array for cardiac MR at 7.0T

PURPOSE

Design, implementation, evaluation, and application of a 32-channel Self-Grounded Bow-Tie (SGBT) transceiver array for cardiac MR (CMR) at 7.0T.

METHODS

The array consists of 32 compact SGBT building blocks. Transmission field ( B 1 + ) shimming and radiofrequency safety assessment were performed with numerical simulations and benchmarked against phantom experiments. In vivo B 1 + efficiency mapping was conducted with actual flip angle imaging. The array's applicability for accelerated high spatial resolution 2D FLASH CINE imaging of the heart was examined in a volunteer study (n = 7).

RESULTS

B 1 + shimming provided a uniform field distribution suitable for female and male subjects. Phantom studies demonstrated an excellent agreement between simulated and measured B 1 + efficiency maps (7% mean difference). The SGBT array afforded a spatial resolution of (0.8 × 0.8 × 2.5) mm³ for 2D CINE FLASH which is by a factor of 12 superior to standardized cardiovascular MR (CMR) protocols. The density of the SGBT array supports 1D acceleration of up to R = 4 (mean signal-to-noise ratio (whole heart) ≥ 16.7, mean contrast-to-noise ratio ≥ 13.5) without impairing image quality significantly.

CONCLUSION

The compact SGBT building block facilitates a modular high-density array that supports accelerated and high spatial resolution CMR at 7.0T. The array provides a technological basis for future clinical assessment of parallel transmission techniques.

Visualization of USPIO-labeled melt-electrowritten scaffolds by non-invasive magnetic resonance imaging

Melt electrowriting (MEW) is a high-resolution fiber-forming technology for the digital fabrication of complex micro-structured scaffolds for tissue engineering, which has convincingly shown its potential in in vitro and in vivo animal studies. The clinical translation of such constructs to the patient requires the capability to visualize them upon implantation with clinically accepted methods such as magnetic resonance imaging (MRI). To this end, this work presents the modification of polycaprolactone (PCL) scaffolds with ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles to render them visualizable by MRI. Composite scaffolds containing up to 0.3 weight % USPIOs were 3D printed by MEW and could be sensitively detected in vitro using T2- and T2*-weighted MRI. At the same time, USPIO incorporation did not affect the usability of PCL for tissue engineering applications as demonstrated by the mechanical and cytocompatibility evaluation. Concentrations up to 0.2% caused small to no decrease in the ultimate tensile strength and Young's modulus. Cytocompatibility tests resulted in excellent cell viability, with proliferating cells adhering to all the scaffolds. This work contributes to the materials library for MEW and opens the possibility of using MRI for longitudinal monitoring of MEW grafts.

Ophthalmic Magnetic Resonance Imaging: Where Are We (Heading To)?

Magnetic resonance imaging of the eye and orbit (MReye) is a cross-domain research field, combining (bio)physics, (bio)engineering, physiology, data sciences and ophthalmology. A growing number of reports document technical innovations of MReye and promote their application in preclinical research and clinical science. Realizing the progress and promises, this review outlines current trends in MReye. Examples of MReye strategies and their clinical relevance are demonstrated. Frontier applications in ocular oncology, refractive surgery, ocular muscle disorders and orbital inflammation are presented and their implications for explorations into ophthalmic diseases are provided. Substantial progress in anatomically detailed, high-spatial resolution MReye of the eye, orbit and optic nerve is demonstrated. Recent developments in MReye of ocular tumors are explored, and its value for personalized eye models derived from machine learning in the treatment planning of uveal melanoma and evaluation of retinoblastoma is highlighted. The potential of MReye for monitoring drug distribution and for improving treatment management and the assessment of individual responses is discussed. To open a window into the eye and into (patho)physiological processes that in the past have been largely inaccessible, advances in MReye at ultrahigh magnetic field strengths are discussed. A concluding section ventures a glance beyond the horizon and explores future directions of MReye across multiple scales, including in vivo electrolyte mapping of sodium and other nuclei. This review underscores the need for the (bio)medical imaging and ophthalmic communities to expand efforts to find solutions to the remaining unsolved problems and technical obstacles of MReye, with the objective to transfer methodological advancements driven by MR physics into genuine clinical value.

Controlled Release of Therapeutics from Thermoresponsive Nanogels: A Thermal Magnetic Resonance Feasibility Study

Thermal magnetic resonance (ThermalMR) accommodates radio frequency (RF)-induced temperature modulation, thermometry, anatomic and functional imaging, and (nano)molecular probing in an integrated RF applicator. This study examines the feasibility of ThermalMR for the controlled release of a model therapeutics from thermoresponsive nanogels using a 7.0-tesla whole-body MR scanner en route to local drug-delivery-based anticancer treatments. The capacity of ThermalMR is demonstrated in a model system involving the release of fluorescein-labeled bovine serum albumin (BSA-FITC, a model therapeutic) from nanometer-scale polymeric networks. These networks contain thermoresponsive polymers that bestow environmental responsiveness to physiologically relevant changes in temperature. The release profile obtained for the reference data derived from a water bath setup used for temperature stimulation is in accordance with the release kinetics deduced from the ThermalMR setup. In conclusion, ThermalMR adds a thermal intervention dimension to an MRI device and provides an ideal testbed for the study of the temperature-induced release of drugs, magnetic resonance (MR) probes, and other agents from thermoresponsive carriers. Integrating diagnostic imaging, temperature intervention, and temperature response control, ThermalMR is conceptually appealing for the study of the role of temperature in biology and disease and for the pursuit of personalized therapeutic drug delivery approaches for better patient care.

A New Framework for Performing Cardiac Strain Analysis from Cine MRI Imaging in Mice

Cardiac magnetic resonance (MR) imaging is one of the most rigorous form of imaging to assess cardiac function in vivo. Strain analysis allows comprehensive assessment of diastolic myocardial function, which is not indicated by measuring systolic functional parameters using with a normal cine imaging module. Due to the small heart size in mice, it is not possible to perform proper tagged imaging to assess strain. Here, we developed a novel deep learning approach for automated quantification of strain from cardiac cine MR images. Our framework starts by an accurate localization of the LV blood pool center-point using a fully convolutional neural network (FCN) architecture. Then, a region of interest (ROI) that contains the LV is extracted from all heart sections. The extracted ROIs are used for the segmentation of the LV cavity and myocardium via a novel FCN architecture. For strain analysis, we developed a Laplace-based approach to track the LV wall points by solving the Laplace equation between the LV contours of each two successive image frames over the cardiac cycle. Following tracking, the strain estimation is performed using the Lagrangian-based approach. This new automated system for strain analysis was validated by comparing the outcome of these analysis with the tagged MR images from the same mice. There were no significant differences between the strain data obtained from our algorithm using cine compared to tagged MR imaging. Furthermore, we demonstrated that our new algorithm can determine the strain differences between normal and diseased hearts.

A Novel Mono-surface Antisymmetric 8Tx/16Rx Coil Array for Parallel Transmit Cardiac MRI in Pigs at 7T

A novel mono-surface antisymmetric 16-element transmit/receive (Tx/Rx) coil array was designed, simulated, constructed, and tested for cardiac magnetic resonance imaging (cMRI) in pigs at 7 T. The cardiac array comprised of a mono-surface 16-loops with two central elements arranged anti-symmetrically and flanked by seven elements on either side. The array was configured for parallel transmit (pTx) mode to have an eight channel transmit and 16-channel receive (8Tx/16Rx) coil array. Electromagnetic (EM) simulations, bench-top measurements, phantom, and MRI experiments with two pig cadavers (68 and 46 kg) were performed. Finally, the coil was used in pilot in-vivo measurements with a 60 kg pig. Flip angle (FA), geometry factor (g-factor), signal-to-noise ratio (SNR) maps, and high-resolution cardiac images were acquired with an in-plane resolution of 0.6 mm × 0.6 mm (in-vivo) and 0.3 mm × 0.3 mm (ex-vivo). The mean g-factor over the heart was 1.26 (R = 6). Static phase [Formula: see text] shimming in a pig body phantom with the optimal phase vectors makes possible to improve the [Formula: see text] homogeneity by factor > 2 and transmit efficiency by factor > 3 compared to zero phases (before RF shimming). Parallel imaging performed in the in-vivo measurements demonstrated well preserved diagnostic quality of the resulting images at acceleration factors up to R = 6. The described hardware design can be adapted for arrays optimized for animals and humans with a larger number of elements (32-64) while maintaining good decoupling for various MRI applications at UHF (e.g., cardiac, head, and spine).

Cardiorenal sodium MRI in small rodents using a quadrature birdcage volume resonator at 9.4 T

OBJECTIVE

Design, implementation, evaluation and application of a quadrature birdcage radiofrequency (RF) resonator tailored for renal and cardiac sodium (²³Na) magnetic resonance imaging (MRI) in rats at 9.4 T.

MATERIALS AND METHODS

A low pass birdcage resonator (16 rungs, d_in = 62 mm) was developed. The transmission field (B₁⁺) was examined with EMF simulations. The scattering parameter (S-parameter) and the quality factor (Q-factor) were measured. For experimental validation B₁⁺-field maps were acquired with the double-angle method. In vivo sodium imaging of the heart (spatial resolution: (1 × 1 × 5) mm³) and kidney (spatial resolution: (1 × 1 × 10) mm³) was performed with a FLASH technique.

RESULTS

The RF resonator exhibits RF characteristics, transmission field homogeneity and penetration that afford ²³Na MR in vivo imaging of the kidney and heart at 9.4 T. For the renal cortex and medulla a SNRs of 8 and 13 were obtained and a SNRs of 14 and 15 were observed for the left and right ventricle.

DISCUSSION

These initial results obtained in vivo in rats using the quadrature birdcage volume RF resonator for ²³Na MRI permit dedicated studies on experimental models of cardiac and renal diseases, which would contribute to translational research of the cardiorenal syndrome.

Toward 19F magnetic resonance thermometry: spin-lattice and spin-spin-relaxation times and temperature dependence of fluorinated drugs at 9.4 T

OBJECTIVE

This study examines the influence of the environmental factor temperature on the ¹⁹F NMR characteristics of fluorinated compounds in phantom studies and in tissue.

MATERIALS AND METHODS

¹⁹F MR mapping and MR spectroscopy techniques were used to characterize the ¹⁹F NMR characteristics of perfluoro-crown ether (PFCE), isoflurane, teriflunomide, and flupentixol. T₁ and T₂ mapping were performed, while temperature in the samples was changed (T = 20-60 °C) and monitored using fiber optic measurements. In tissue, T₁ of PFCE nanoparticles was determined at physiological temperatures and compared with the T_1-measured at room temperature.

RESULTS

Studies on PFCE, isoflurane, teriflunomide, and flupentixol showed a relationship between temperature and their physicochemical characteristics, namely, chemical shift, T₁ and T₂. T₁ of PFCE nanoparticles was higher at physiological body temperatures compared to room temperature.

DISCUSSION

The impact of temperature on the ¹⁹F NMR parameters of fluorinated compounds demonstrated in this study not only opens a trajectory toward ¹⁹F MR-based thermometry, but also indicates the need for adapting MR sequence parameters according to environmental changes such as temperature. This will be an absolute requirement for detecting fluorinated compounds by ¹⁹F MR techniques in vivo.

Optimal site selection and image fusion guidance technology to facilitate cardiac resynchronization therapy

INTRODUCTION

Cardiac resynchronization therapy (CRT) has emerged as one of the few effective treatments for heart failure. However, up to 50% of patients derive no benefit. Suboptimal left ventricle (LV) lead position is a potential cause of poor outcomes while targeted lead deployment has been associated with enhanced response rates. Image-fusion guidance systems represent a novel approach to CRT delivery, allowing physicians to both accurately track and target a specific location during LV lead deployment.

AREAS COVERED

This review will provide a comprehensive evaluation of how to define the optimal pacing site. We will evaluate the evidence for delivering targeted LV stimulation at sites displaying favorable viability or advantageous mechanical or electrical properties. Finally, we will evaluate several emerging image-fusion guidance systems which aim to facilitate optimal site selection during CRT.

EXPERT COMMENTARY

Targeted LV lead deployment is associated with reductions in morbidity and mortality. Assessment of tissue characterization and electrical latency are critical and can be achieved in a number of ways. Ultimately, the constraints of coronary sinus anatomy have forced the exploration of novel means of delivering CRT including endocardial pacing which hold promise for the future of CRT delivery.

Myocardial Effective Transverse Relaxation Time T 2* is Elevated in Hypertrophic Cardiomyopathy: A 7.0 T Magnetic Resonance Imaging Study

Hypertrophic cardiomyopathy (HCM) is the most common genetic disease of the myocardium and bares the risk of progression to heart failure or sudden cardiac death. Identifying patients at risk remains an unmet need. Recognizing the dependence of microscopic susceptibility on tissue microstructure and on cardiac macromorphology we hypothesized that myocardial T2* might be altered in HCM patients compared to healthy controls. To test this hypothesis, myocardial T2*-mapping was conducted at 7.0 Tesla to enhance T2*-contrast. 2D CINE T2*-mapping was performed in healthy controls and HCM patients. To ensure that T2* is not dominated by macroscopic magnetic field inhomogeneities, volume selective B0 shimming was applied. T2* changes in the interventricular septum across the cardiac cycle were analyzed together with left ventricular radius and ventricular septal wall thickness. The results show that myocardial T2* is elevated throughout the cardiac cycle in HCM patients compared to healthy controls. A mean septal T2* = 13.7 ± 1.1 ms (end-systole: T2*,systole = 15.0 ± 2.1, end-diastole: T2*,diastole = 13.4 ± 1.3 ms, T2*,systole/T2*,diastole ratio = 1.12) was observed in healthy controls. For HCM patients a mean septal T2* = 17.4 ± 1.4 ms (end-systole: T2*,systole = 17.7 ± 1.2 ms, end-diastole: T2*,diastole = 16.2 ± 2.5 ms, T2*,systole/T2*,diastole ratio = 1.09) was found. Our preliminary results provide encouragement that assessment of T2* and its changes across the cardiac cycle may benefit myocardial tissue characterization in HCM.

Open Source 3D Multipurpose Measurement System with Submillimetre Fidelity and First Application in Magnetic Resonance

Magnetic resonance imaging (MRI) is the mainstay of diagnostic imaging, a versatile instrument for clinical science and the subject of intense research interest. Advancing clinical science, research and technology of MRI requires high fidelity measurements in quantity, location and time of the given physical property. To meet this goal a broad spectrum of commercial measurement systems has been made available. These instruments frequently share in common that they are costly and typically employ closed proprietary hardware and software. This shortcoming makes any adjustment for a specified application difficult if not prohibitive. Recognizing this limitation this work presents COSI Measure, an automated open source measurement system that provides submillimetre resolution, robust configuration and a large working volume to support a versatile range of applications. The submillimetre fidelity and reproducibility/backlash performance were evaluated experimentally. Magnetic field mapping of a single ring Halbach magnet, a 3.0 T and a 7.0 T MR scanner as well as temperature mapping of a radio frequency coil were successfully conducted. Due to its open source nature and versatile construction, the system can be easily modified for other applications. In a resource limited research setting, COSI Measure makes efficient use of laboratory space, financial resources and collaborative efforts.