Interleaved spiral‐in/out with application to functional MRI (fMRI)

The conventional spiral‐in/out trajectory samples k‐space sufficiently in the spiral‐in path and sufficiently in the spiral‐out path to enable creation of separate images. We propose an “interleaved spiral‐in/out” trajectory comprising a spiral‐in path that gathers one half of the k‐space data, and a complimentary spiral‐out path that gathers the other half. The readout duration is thereby reduced by approximately half, offering two distinct advantages: reduction of signal dropout due to susceptibility‐induced field gradients (at the expense of signal‐to‐noise ratio [SNR]), and the ability to achieve higher spatial resolution when the readout duration is identical to the conventional method. Two reconstruction methods are described; both involve temporal filtering to remove aliasing artifacts. Empirically, interleaved spiral‐in/out images are free from false activation resulting from signal pileup around the air/tissue interface, which is common in the conventional spiral‐out method. Comparisons with conventional methods using a hyperoxia stimulus reveal greater frontal‐orbital activation volumes but a slight reduction of overall activation in other brain regions. Magn Reson Med, 2009. © 2009 Wiley‐Liss, Inc.