Compartment-based Reconstruction of 3D Acquisition-Weighted 31 P Cardiac MRSI at 7T - a Reproducibility Study

PURPOSE: Even at 7T, cardiac 31 P MRSI is fundamentally limited by low SNR, leading to long scan times and poor temporal and spatial resolutions. Compartment-based reconstruction algorithms such as magnetic resonance spectroscopy with linear algebraic modelling (SLAM) and spectral localization by imaging (SLIM) may improve SNR or reduce scan time without changes to acquisition. Here we compare the repeatability and SNR performance of these compartment-based methods, applied to three different acquisition schemes at 7T. METHODS: 12 healthy volunteers were scanned twice. Each scan session consisted of a 6.5 minute 3D acquisition-weighted (AW) cardiac 31 P phase-encode based MRSI acquisition and two 6.5 minute truncated k-space acquisitions with increased averaging (4 × 4 × 4 central k-space phase encodes and fSLAM optimized k-space phase encodes). Spectra were reconstructed using: (i) AW Fourier-reconstruction; (ii) AW SLAM; (iii) AW SLIM; (iv) 4 × 4 × 4 SLAM; (v) 4 × 4 × 4 SLIM; and (vi) fSLAM optimized SLAM (fSLAM) acquisition-reconstruction combinations. The PCr/ATP ratio, the PCr SNR, and spatial response functions were computed, in addition to coefficients of reproducibility and variability. RESULTS: Using the compartment-based reconstruction algorithms with the AW 31 P acquisition resulted in a significant increase in SNR compared to previously published Fourier-based MRSI reconstruction methods, while maintaining the measured phosphocreatine-to-adenosine triphosphate ratio and improving inter-scan reproducibility. The alternative acquisition strategies with truncated k-space performed no better than the common AW approach. CONCLUSION: Compartment-based spectroscopy approaches provide an attractive reconstruction method for cardiac 31 P spectroscopy at 7T, improving reproducibility and SNR without the need for a dedicated k-space sampling strategy.