7T 19F/1H MRI with perfluorocarbon-labeled immune cells in pigs: Pilot results with a dedicated twin-array system with pTX support

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 19F-labeled immune cells. The high Larmor frequency of 19F (∼95% of that for 1H-nuclei) leads to similar technical hurdles in acquiring MR images at UHF that originate from the heterogeneity of B1+. We aimed to develop a system of transmit/receive (Tx/Rx) arrays exploiting parallel transmit (pTX) technology for B1+-shimming to acquire a combination of high-quality anatomical 1H MR-images of a pig heart and 19F images of labeled immune cells at 7T.
Method: The 16-element twin-arrays for 1H and 19F nuclei were designed using electromagnetic simulations with a focus on optimal B1-shimming and g-factor in the region of the pig heart. pTX support allows for the subject-specific B1-shimming for 1H cardiac MRI and transfer of settings for the B1-shimming to the 19F 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 B1+ shimming setting between the 1H to 19F 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 19F-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.