Abstract
PURPOSE: Cardiac inflammation plays a key role in many diseases. However, its underlying mechanisms and progression remain poorly understood. Using an ultra-high field (UHF) may increase the sensitivity of MRI of inflammatory processes with (19)F-labeled immune cells. The high Larmor frequency of (19)F (∼95% of that for (1)H-nuclei) leads to similar technical hurdles in acquiring MR images at UHF that originate from the heterogeneity of B(1) (+). We aimed to develop a system of transmit/receive (Tx/Rx) arrays exploiting parallel transmit (pTX) technology for B(1) (+)-shimming to acquire a combination of high-quality anatomical (1)H MR-images of a pig heart and (19)F images of labeled immune cells at 7T. METHOD: The 16-element twin-arrays for (1)H and (19)F nuclei were designed using electromagnetic simulations with a focus on optimal B(1)-shimming and g-factor in the region of the pig heart. pTX support allows for the subject-specific B(1)-shimming for (1)H cardiac MRI and transfer of settings for the B(1)-shimming to the (19)F twin-array. RESULTS: The twin-array system was implemented and tested in a pig-thorax--shaped phantom, in-vivo in a myocardial infarction pig model, and in an excised heart. A transfer of static B(1)+ shimming setting between the (1)H to (19)F arrays was demonstrated. The parallel imaging acceleration of up to a factor 4 was possible with a g-factor <1.3 for both arrays. The 7T MRI of (19)F-labeled immune cells in the heart of the pig was demonstrated both in-vivo and ex-vivo. CONCLUSION: The 7T MRI of perfluorocarbon-labeled immune cells in a large-animal myocardial infarction model becomes feasible using a novel dedicated twin-arrays system.