Regionally resolved cardiac metabolism using a dipole‐loop array coil for 7 T 31 P ‐ MRSI

Abstract Purpose We introduce a novel commercial phosphorus‐31 ( 31 P) dipole‐loop array coil, describing the coil hardware and testing its performance on phantoms. We used this coil to assess cardiac metabolism per region in healthy volunteers. Methods B 1 + field maps were simulated and compared to maps measured with a set of CSI sequences with varying voltages. Seventeen volunteers were scanned with 7 T phosphorus‐31 magnetic resonance spectroscopic imaging ( 31 P‐MRSI). Reproducibility was assessed in nine of these volunteers. Strain was measured for six of these volunteers at 3 T. Results Blood‐ and saturation‐corrected Phosphocreatine/γ‐adenosine triphosphate (PCr/ATP) ratios were measured for four regions of the left ventricle: 1.86 in septum, 2.25 in anterior wall, 1.41 in inferior wall, and 1.53 in lateral wall, respectively. These are in the expected range compared to previous studies. B 1 + maps show good signal uniformity around the position of the heart (0.13 ± 0.06 μT/sqrt(W)). Intrasession and intersession coefficients of reproducibility were 0.22–0.88 and 0.29–0.79, respectively. Linear modeling shows that regional PCr/γATP correlates with circumferential strain but not radial strain. This requires corroboration by a larger study including patients with impaired function and energetics. Conclusion Dipole‐loop array coils present a promising new approach for human cardiac 31 P‐MRSI at 7 T. Their favorable B 1 + uniformity at depth and specific absorption rate over loop arrays and improved SNR when combined with loops for reception could be beneficial for further clinical studies measuring energetics by 31 P‐MRSI at 7 T. The new capability to assess PCr/γATP ratios across the whole left ventricle could enable clinical studies to investigate regional changes in cardiac energetics for the first time.