Pitfalls of data-driven tSNR optimized coil combination for fMRI

Summary of Main Findings: Analytical expressions for optimal tSNR and t-score for the mean coil combinations are described and compared to the commonly used covSoS coil combination. Findings suggest that optimal tSNR or t-score for the mean do not guarantee better BOLD signal detection in fMRI time series. Synopsis: For MRI with a multi-receiver RF coil, one image per coil element and per time frame is obtained. The final image is typically calculated from the root sum of squares (rSoS) combination across channels. While this combination approach is quasi-optimal for SNR, it is not necessarily optimal for temporal SNR (tSNR) of the time-series. We present two analytical and voxel-wise coil combination expressions reaching optimality in tSNR and t-score for the mean (TSM) respectively. Their BOLD sensitivity is compared to the gold standard covariance root sum of squares. Both improved tSNR and TSM but yielded weaker t-scores than covSoS.