Myocardial T2* Mapping with Ultrahigh Field Magnetic Resonance: Physics and Frontier Applications

Abstract

Cardiovascular magnetic resonance imaging (CMR) has become an indispensable clinical tool for the assessment of morphology, function and structure of the heart muscle. By exploiting quantification of the effective transverse relaxation time (T 2 * ) CMR also affords myocardial tissue characterization and probing of cardiac physiology, both being in the focus of ongoing research. These developments are fueled by the move to ultrahigh magnetic field strengths, which permits enhanced sensitivity and spatial resolution that help to overcome limitations of current clinical MR systems with the goal to contribute to a better understanding of myocardial (patho)physiology in vivo. In this context, the aim of this report is to introduce myocardial T 2 * mapping at ultrahigh magnetic fields as a promising technique to non-invasively assess myocardial (patho)physiology. For this purpose the basic principles of T 2 * assessment, the biophysical mechanisms determining T 2 * and (pre)clinical applications of myocardial T 2 * mapping are presented.Technological challenges and solutions for T 2 * sensitized CMR at ultrahigh magnetic field strengths are discussed followed by a review of acquisition techniques and post-processing approaches. Preliminary results derived from myocardial T 2 * mapping in healthy subjects and cardiac patients at 7.0 T are presented. A concluding section discusses remaining questions and challenges and provides an outlook on future developments and potential clinical applications.

Recent Advances of Bioresponsive Nano-Sized Contrast Agents for Ultra-High-Field Magnetic Resonance Imaging

“…It is well-recognized that ultra-high-field MRI has achieved the increasing prevalence in both fundamental research and clinical applications (Dyke et al, 2017;Huelnhagen et al, 2017;Lehericy et al, 2017;Hametner et al, 2018). A bimodal contrast agent of Dy 3+ (DOTA)/Cy7.5-conjugated tobacco mosaic virus (TMV) was developed for ultra-high-field MRI, confirming its high transverse relaxivity r 2 and suitable for both NIRF imaging and T 2 MRI in cancel cells diagnosis (Hu et al, 2017).…”

Cardiac T2* mapping: Techniques and clinical applications

“…To link the T 2 * value acquired at 3.0T to its corresponding 1.5T T 2 * value, some studies proposed a conversion relationship 18,32 . Moreover, at 7.0T, acquisition techniques were introduced to reduce the influence of the substantial macroscopic magnetic field inhomogeneities in T 2 * measurement 33–35 . It is known that B 0 and B 1 inhomogeneities increase with the magnetic field strength 36 .…”

“…It is known that B 0 and B 1 inhomogeneities increase with the magnetic field strength 36 . However, a high field benefits dynamic myocardial T 2 * mapping, better information of myocardial microstructure, visualization of myocardial fibers, detection of coronary artery stenosis, and the detection of myocardial reperfusion hemorrhage 33,34,37 …”

B0 shimming of the human heart at 7T

“…In addition, the temporal B 0 ‐field variations between different cardiac phases are not addressed in the standard vendor‐supplied B 0 ‐shim protocols. The vendor‐supplied shimming is performed for a cuboid‐shaped volume, which is typically adjusted to the whole heart 27,28 . However, B 0 shimming targeted to an anatomy‐driven shim region of interest (SROI) improved the field homogeneity in the heart at 3 T 8,29 .…”

“…The vendor-supplied shimming is performed for a cuboid-shaped volume, which is typically adjusted to the whole heart. 27,28 However, B 0 shimming targeted to an Conclusion: Challenges in state-of-the-art B 0 shimming of the human heart at 7 T were described. Cardiac phase-specific shimming strategies were found to be superior to vendor-supplied shimming.…”