A Flexible Array for Cardiac 31P MR Spectroscopy at 7 T

Abstract

The simulation optimization and implementation of a flexible 31 P transmit/receive coil array, under the geometrical constraint of fitting into the housing of an already existing 12-channel proton array, to enable localized cardiac 31 P MRS at 7 T is presented. Methods: The performance in terms of homogeneity, power and SAR efficiency, and receive benchmark of 32 potential array designs was compared by full wave 3D electromagnetic simulation considering the respective optimal static B + 1 shims. The design with the best performance was built and compared to a commercially available single loop in simulation and measurement. Results: Simulation revealed an optimal array design comprising three overlapping elements, each sized 94 × 141 mm 2. Simulation comparison with a single loop coil predicted a performance increase due to increased power efficiency and lower SAR values. This was verified by phantom measurements, where an SNR increase of 46% could be observed for localized 31 P spectroscopy in a voxel positioned comparable to an in vivo cardiac measurement scenario. Conclusion: A flexible 31 P/ 1 H RF coil array with improved SNR is presented, enabling localized in vivo cardiac 31 P spectroscopy at 7 T.

In Vivo Magnetic Resonance Spectroscopy Methods for Investigating Cardiac Metabolism

“…These studies aim to eventually include dynamic shim updating on the selected volume in the heart, as has been experimented with within the brain studies at ultra-high-field ≥7 Tesla [67,68]. Overall considerations on the heart shimming include: (i) using slab-selective approaches shimming to minimize the field distribution variations (shimming standard deviation (SD)), (ii) optimizing high-order shims, (iii) temporal B 0 -field variations with regards to cardiac cycle and respirationinduced, (iv) shimming of oblique orientations, (v) develop dynamic shimming interface by rapid field mapping using slab-specific or cardiac phase-specific mapping sets, and (vi) the emerging use of artificial intelligence in compensating the field variations [45,63,66,[69][70][71].…”