Self-navigated spiral fMRI: interleaved versus single-shot.

This study compares the measured activation volumes in motor cortex as well as the fluctuation noise and off-resonance characteristics for 1-, 2-, and 4-shot spiral gradient-recalled echo blood oxygen level dependent contrast functional magnetic resonance imaging (fMRI) acquisitions, under conditions of constant resolution and scan time and with two readout durations. Reconstructions were made with and without self-navigator correction. It was found that the navigator correction provided a 50% reduction in image fluctuation noise with 4-shot acquisitions, and that multishot acquisitions perform as well as single-shot techniques when self-navigation is employed. An analysis of blurring showed that off-resonance delta f causes blurring when delta f > 1/(2*Tad), where Tad is the readout duration. Off-resonance effects were readily corrected during reconstruction with retrospective linear shim, even with the longer readout duration needed for single-shot methods. With navigator and shim correction, single-shot and multishot spiral methods are highly effective for fMRI acquisitions.