Advanced Knee ASL Imaging at 7T

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 ASL imaging of knee epiphyseal bone marrow is challenging because ASL imaging is a low signal-to-noise ratio technique, and the perfusion level is significantly low in epiphyseal yellow bone marrow mainly consisting of fat cells with a sparse network of capillaries. 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 and establish an optimized, safe, and efficient parallel transmit (pTx) platform for new pTx-integrated knee ASL imaging methods and explore their clinical potentials in juvenile osteochondritis dissecans (JOCD) patients. We will develop an optimized, safe, and efficient pTx platform for knee ASL imaging by developing a novel 32-channel loop-dipole transmit and receive array knee coil, building a VOP library using 13 human models from the Virtual Family (including morphed models) and evaluating alternative strategies for highly efficient knee ASL imaging, such as utilizing population-matched safety factors for adults and juveniles, respectively. We will develop and optimize pTx-integrated knee ASL imaging methods that will utilize optimized pTx RF pulses. We will also explore the clinical potentials of 7T knee ASL imaging in JOCD in terms of its ability in predicting 6- and 12-month healing status and differentiating patients with and without stable lesions and evaluate the diagnostic and prognostic performance of bone marrow blood flow measures using receiver operating characteristics (ROC) curve analyses. We will also develop a novel multivariate logistic regression model with a new nomogram to predict the healing status after 6, 12 months of nonoperative treatment.