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

ABSTRACT 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 31 P MRS acquisition times and the use of more advanced energetics‐probing techniques in clinical studies.