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- Title
Optimized EPI for fMRI studies of the orbitofrontal cortex: compensation of susceptibility-induced gradients in the readout direction.
- Authors
Nikolaus Weiskopf; Chloe Hutton; Oliver Josephs; Robert Turner; Ralf Deichmann
- Abstract
Abstract??ObjectMost functional magnetic resonance imaging (fMRI) studies record the blood oxygen leveldependent (BOLD) signal using gradient-echo echo-planar imaging (GE EPI). EPI can suffer from substantial BOLD sensitivity loss caused by magnetic field inhomogeneities. Here, BOLD sensitivity losses due to susceptibility- induced gradients in the readout (RO) direction are characterized and a compensation approach is developed.Materials and MethodsBased on a theory describing the dropout mechanism, an EPI sequence was optimized for maximal BOLD sensitivity in the orbitofrontal cortex (OFC) using a specific combination of an increased spatial resolution in the RO direction and a reduced echo time. Using measured BOLD sensitivity maps and a breath hold experiment, the model and compensation approach were tested.ResultsUsing typical fMRI EPI parameters, susceptibility-induced gradients in the RO direction caused dropouts in the OFC and the inferior temporal lobe. Optimizing the echo time and spatial resolution effectively reduced the dropout as predicted by the theory.ConclusionThe model-based compensation approach effectively reduces BOLD sensitivity losses due to susceptibility-induced gradients in the RO direction. It retains the high temporal resolution of single-shot EPI and can be readily combined with methods for the compensation of susceptibility-induced field gradients in the phase-encoding and through-plane direction.
- Subjects
MAGNETIC resonance imaging; BLOOD; OXYGEN; CEREBRAL cortex
- Publication
MAGMA: Magnetic Resonance Materials in Physics, Biology & Medicine, 2007, Vol 20, Issue 1, p39
- ISSN
0968-5243
- Publication type
Article
- DOI
10.1007/s10334-006-0067-6