Enhanced sensitivity with fast three-dimensional blood-oxygen-level-dependent functional MRI: comparison of SENSE-PRESTO and 2D-EPI at 3 T.

A major impetus in functional MRI development is to enhance sensitivity to changes in neural activity. One way to improve sensitivity is to enhance contrast to noise ratio, for instance by increasing field strength or the number of receiving coils. If these parameters are fixed, there is still the possibility to optimize scans by altering speed or signal strength [signal-to-noise ratio (SNR)]. We here demonstrate a very fast whole-brain scan, by combining a three-dimensional (3D)-PRESTO (principle of echo shifting with a train of observations) pulse sequence with a commercial eight-channel head coil and sensitivity encoding (SENSE). 3D-PRESTO uses time optimally by means of echo shifting. Moreover, 3D scans can accommodate SENSE in two directions, reducing scan time proportionally. The present PRESTO-SENSE sequence achieves full brain coverage within 500 ms. We compared this with a two-dimensional (2D) echo planar imaging (EPI) scan with identical brain coverage on 10 volunteers. Resting-state temporal SNR in the blood-oxygen-level-dependent (BOLD) frequency range and T-statistics for thumb movement and visual checkerboard activations were compared. Results show improved temporal SNR across the brain for PRESTO-SENSE compared with EPI. The percentage signal change and relative standard deviation of the noise were smaller for PRESTO-SENSE. Sensitivity for brain activation, as reflected by T-values, was consistently higher for PRESTO, and this seemed to be mainly due to the increased number of observations within a fixed time period. We conclude that PRESTO accelerated with SENSE in two directions can be more sensitive to BOLD signal changes than the widely used 2D-EPI, when a fixed amount of time is available for functional MRI scanning.