Optimized EPI for fMRI studies of the orbitofrontal cortex.
A common problem in gradient-echo echo planar imaging (EPI) is the occurrence of image distortions and signal losses caused by susceptibility gradients near air/tissue interfaces. Since EPI is frequently used for functional magnetic resonance imaging experiments based on the blood oxygenation level-dependent effect, functional studies of certain brain regions affected by susceptibility gradients, such as the temporal lobes and the orbitofrontal cortex, may be compromised. In this work a method for signal recovery in certain regions of the orbitofrontal cortex is presented. The influence of in-plane susceptibility gradients is reduced by optimization of the imaging slice orientation. Through-plane susceptibility gradients are partly compensated by means of a moderate preparation gradient pulse similar to z-shimming. In contrast to several other techniques proposed in the literature for reducing susceptibility effects, this method does not compromise the temporal resolution and is therefore applicable to event-related studies.
Deichmann
R
R
Wellcome Department of Imaging Neuroscience, Institute of Neurology, London WC1N 3BG, UK. r.deichmann@fil.ion.ucl.ac.uk
Gottfried
J A
JA
Hutton
C
C
Turner
R
R
D000465:Algorithms; D016477:Artifacts; D001931:Brain Mapping / Q000379:methods; D017352:Echo-Planar Imaging / Q000379:methods*; D005071:Evoked Potentials / Q000502:physiology; D005625:Frontal Lobe / Q000502:physiology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008432:Mathematical Computing; D010101:Oxygen Consumption / Q000502:physiology; D012016:Reference Values; D012680:Sensitivity and Specificity