SSFP Cardiovascular MR Imaging on 3.0T Using Unified-Coil Local Shimming

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Abstract Cardiovascular disease is the leading cause of death globally. Cardiovascular magnetic resonance (CMR) is routinely used in the clinical management of cardiovascular disease and is the standard method for the assessment of cardiac function and myocardial tissue properties. Today, most clinical CMR studies are still conducted on 1.5T scanners because of their availability and robustness in executing CMR protocols. In general, 3.0T provides higher SNR, spatial resolution, and reduced scan time than 1.5T. However, the increased B0 field strength also poses technical challenges for CMR. A major challenge is the susceptibility or off-resonance artifacts due to worsened B0 field inhomogeneity. In the last two decades, steady-state free precession (SSFP) has revolutionized CMR on 1.5T because it boosts SNR and contrast to noise ratio (CNR) markedly over gradient-echo based acquisitions. However, its routine use on 3.0T has been inconsistent despite continuously improving B0 homogeneity and shimming capabilities. Therefore, gradient-echo based acquisitions are still routinely used, such as for cine imaging, cardiac relaxometry, and coronary MRA, negating the major advantages of 3.0T for CMR. Due to the distance of standard whole-body shimming coils from the target organ, they only provide shimming capabilities up to the second-order spherical harmonic (SH), and are incapable of shimming higher-order localized field variations such as those present near the heart-lung interface. This remains an unmet challenge. In this project, we will apply a novel unified shim-RF coil technique to overcome the primary limitation in 3.0T CMR. We will develop a unified shim-RF coil and validate its safety and high-order shimming capability (Aim 1). We will develop a respiratory motion-resolved B0 field mapping technique based on our low-rank Multitasking framework and real-time shim circuits to allow dynamic shimming for free breathing CMR (Aim 2). We will then validate the technology in human subjects on 3.0T (Aim 3). Successful completion of this project will enable robust SSFP CMR on 3.0T, a major technical challenge, which allows reliable high-resolution, high- SNR CMR, including but not limited to cine and coronary MRA. This novel cardiac shimming system has the potential to have a major impact in accelerating the clinical adoption of 3.0T CMR.