The Goldilocks zone for 3T MRS studies using semi-LASER: Determining the optimal balance between repetition time and scan time using FSL-MRS

Motivation: A short TR is often used in clinical MRS brain studies, leading to T1-weighting of metabolites and inaccurate T1 correction. Goal(s): To determine the optimal balance between scan time and TR that minimizes T1-weighting effects when using semi-LASER MRS. Approach: SNR and metabolite concentrations were compared for TRs of 2, 5 and 8s using FSL-MRS. Results: A TR of 5s provides a good balance of scan time, SNR and signal recovery. For a similar scan time, TR of 2s leads to incomplete signal recovery and thus heavy T1 weighting, while a TR of 8s results in complete signal recovery but reduced SNR. Impact: For MRS studies using semi-LASER, our work informs scientists and clinicians on the issues of using a short TR, and recommends the optimal scan parameters to use while implementing the newly available FSL-MRS analysis package.