Reproducibility of human cardiac phosphorus MRS (31P-MRS) at 7 T

Purpose We test the reproducibility of human cardiac phosphorus MRS (P-31-MRS) at ultra-high field strength (7 T) for the first time. The primary motivation of this work was to assess the reproducibility of a 'rapid' 61/2 min P-31 three-dimensional chemical shift imaging (3D-CSI) sequence, which if sufficiently reproducible would allow the study of stress-response processes. We compare this with an established 28 min protocol, designed to record high-quality spectra in a clinically feasible scan time. Finally, we use this opportunity to compare the effect of per-subject B-0 shimming on data quality and reproducibility in the 61/2 min protocol. Methods 10 healthy subjects were scanned on two occasions: one to test the 28 min 3D-CSI protocol, and one to test the 61/2 min protocol. Spectra were fitted using the OXSA MATLAB toolbox. The phosphocreatine to adenosine triphosphate concentration ratio (PCr/ATP) from each scan was analysed for intra- and intersubject variability. The impact of different strategies for voxel selection was assessed. Results There were no significant differences between repeated measurements in the same subject. For the 28 min protocol, PCr/ATP in the midseptal voxel across all scans was 1.91 +/- 0.36 (mean +/- intersubject SD). For the 61/2 min protocol, PCr/ATP in the midseptal voxel was 1.76 +/- 0.40. The coefficients of reproducibility (CRs) were 0.49 (28 min) and 0.67 (61/2 min). Per-subject B-0 shimming improved the fitted PCr/ATP precision (for 61/2 min scans), but had negligible effect on the CR (0.67 versus 0.66). Conclusions Both 7 T protocols show improved reproducibility compared with a previous 3 T study by Tyler et al. Our results will enable informed power calculations and protocol selection for future clinical research studies.