Repeatability of Rapid Human Cardiac Phosphorus MRSI (³¹P-MRSI) Using Concentric Ring Trajectory Readouts at 7 T

Purpose: PCr/ATP ratio is determined at 7 T typically using Fourier-transform based magnetic resonance spectroscopic imaging sequences (FT-MRSI). These sequences require acquisition times longer than desirable for inclusion in cardiac clinical trials. Concentric ring trajectory (CRT-MRSI) has been described as an accelerated alternative k-space sampling method. In this work we aim to establish the inter- and intra-session repeatability of three different CRT protocols and compare their voxel-based PCr/ATP ratios to compartment-based PCr/ATP values extracted with spectroscopy using a linear algebraic model (SLAM) method. Methods: Seven healthy volunteers were scanned twice on two different days. Each time a 6.5-min 3D FT-MRSI acquisition with 10 × 10 × 10 resolution was followed by a 2.5-min CRT-MRSI with matched resolution, a 1.5-min CRT-MRSI with matched resolution, and a 6.9-min CRT-MRSI with 12 × 12 × 12 resolution. Spectra from a mid-septal voxel and the cardiac compartment were fitted with the OXSA toolbox. PCr/ATP ratio was quantified for inter- and intra-session repeatability analysis. Results: Paired repeated measurements were not significantly different within subjects. Good inter- and intra-session agreement was observed between FT-MRSI and each CRT-MRSI protocol. CRT-MRSI protocols all had larger coefficients of repeatability (CoR) than FT-MRSI. CRT-SLAM-based PCr/ATP values had lower CoR than voxel-based data except for 2.5-min CRT-SLAM, and high-resolution CRT-SLAM had lower inter-session CoR compared to FT-MRSI (1.42 vs. 2.21). Conclusion: We established the repeatability of CRT-MRSI-based PCr/ATP values and showed higher SNR and lower CoR for CRT-SLAM. Our findings allow shorter ³¹P MRS acquisition times and the use of more advanced energetics-probing techniques in clinical studies.