Advanced Knee ASL Imaging at 7T

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Abstract Bone marrow perfusion can provide essential knowledge about bone physiology, improve our understanding of disease etiology and pathophysiology, assist the differentiation between normal and abnormal bone marrow, and assess the response to prescribed therapies. Arterial spin labeling (ASL) magnetic resonance imaging (MRI), as a noninvasive and non-contrast-enhanced approach, is well suited for longitudinal monitoring of disease progression and routine evaluation of therapy response. But as revealed by our recent studies, there exist technical challenges (e.g., low signal-to-noise (SNR) ratio due to significantly low perfusion in epiphyseal yellow bone marrow mainly consisting of fat cells with a sparse network of capillaries), and methodological limitations (e.g., single slice coverage and impractically long acquisition time for multi-slice imaging at 3T), hampering routine application of ASL imaging in the knee. Ultrahigh (≥7T) magnetic field can specifically benefit ASL imaging and overcome these challenges by increasing SNR, prolonging blood and tissue T1, and improving parallel imaging performance. However, the current clinically approved single-transmit MRI system and associated imaging methods are incapable of managing the transmit B1 (B1+) fields needed to realize the promised improvement in imaging quality, reliability, and robustness of 7T while existing RF coils are unable to provide adequate B1+ coverage for optimal ASL imaging. Our long-term goal is to develop and improve UHF imaging methods to better facilitate scientific research and clinical studies to improve the management of skeletal diseases and patient healthcare. The rationale is that the existing technical challenges for UHF imaging, including ASL, can be overcome or mitigated, ultimately to realize UHF potentials with promised benefits and superior imaging ability. The objective of this proposal is to develop an optimized, safe, and efficient pTx platform for knee ASL imaging (Aim 1), to develop and optimize pTx-integrated knee ASL imaging methods (Aim 2) and to explore their clinical potentials via studies with a cohort of JOCD patients, an ideal testbed for the developed methodologies. Accomplishing these aims will enable us to fully explore and utilize pTx potentials to overcome the existing technical challenges for knee ASL imaging at 7T. Once developed and optimized, the ASL methods, along with the pTx knee imaging platform, will provide clinicians and research community a powerful tool to enrich our insights into disease etiology and pathophysiology and improve the management of not only JOCD but also various impactful common knee diseases (e.g., osteoarthritis). Novel knowledge and experience from our pioneering development will speed up the maturity of new technology toward early approval of the next generation of clinical UHF MRI systems.