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

TLDR

BOLD fMRI suffers from signal dropout in orbitofrontal and parietal regions caused by magnetic field gradients near air‑tissue interfaces. This study reports the use of spiral‑in and spiral‑in/out k‑space trajectories that start at the periphery and end at the center, followed by a conventional spiral‑out readout. The spiral‑in and spiral‑out images are combined in multiple ways to simultaneously increase signal‑to‑noise ratio and reduce dropout artifacts. The spiral‑in trajectory lowers dropout, enhances BOLD contrast, and, in olfactory activation experiments, yields larger activation volumes and higher SNR across all regions. Magn Reson Med 46:515–522, 2001; © 2001 Wiley‑Liss, Inc.

Abstract

Abstract BOLD fMRI is hampered by dropout of signal in the orbitofrontal and parietal 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. The 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 simultaneously achieve increased signal‐to‐noise ratio (SNR) and reduced dropout artifacts. Activation experiments employing an olfaction task demonstrate significantly increased activation volumes due to reduced dropout, and overall increased SNR in all regions. Magn Reson Med 46:515–522, 2001. © 2001 Wiley‐Liss, Inc.