Spiral-in/out BOLD fMRI for increased SNR and reduced susceptibility artifacts

BOLD fMRI is hampered by dropout of signal in the orbitofrontal and parieta l brain regions due to magnetic field gradients near air-tissue interfaces. This work reports the use of spiral-in trajectories that begin at the edge of k-space and end at the origin, and spiral in/out trajectories in which a spiral-in readout is followed by a conventional spiral-out trajectory. Th e spiral-in trajectory reduces the dropout and increases the BOLD contrast. The spiral-in and spiral-out images can be combined in several ways to sim ultaneously achieve increased signal-to-noise ratio (SNR) and reduced dropo ut artifacts. Activation experiments employing an olfaction task demonstrat e significantly increased activation volumes due to reduced dropout, and ov erall increased SNR in all regions. (C) 2001 Wiley-Liss, Inc.