title: Increased BOLD sensitivity in the orbitofrontal cortex using slice-dependent echo times at 3 T.
abstract: Functional magnetic resonance imaging (fMRI) exploits the blood oxygenation level dependent (BOLD) effect to detect neuronal activation related to various experimental paradigms. Some of these, such as reversal learning, involve the orbitofrontal cortex and its interaction with other brain regions like the amygdala, striatum or dorsolateral prefrontal cortex. These paradigms are commonly investigated with event-related methods and gradient echo-planar imaging (EPI) with short echo time of 27 ms. However, susceptibility-induced signal losses and image distortions in the orbitofrontal cortex are still a problem for this optimized sequence as this brain region consists of several slices with different optimal echo times. An EPI sequence with slice-dependent echo times is suitable to maximize BOLD sensitivity in all slices and might thus improve signal detection in the orbitofrontal cortex. To test this hypothesis, we first optimized echo times via BOLD sensitivity simulation. Second, we measured 12 healthy volunteers using a standard EPI sequence with an echo time of 27 ms and a modified EPI sequence with echo times ranging from 22 ms to 47 ms. In the orbitofrontal cortex, the number of activated voxels increased from 87 ± 44 to 549 ± 83 and the maximal t-value increased from 4.4 ± 0.3 to 5.4 ± 0.3 when the modified EPI was used. We conclude that an EPI with slice-dependent echo times may be a valuable tool to mitigate susceptibility artifacts in event-related whole-brain fMRI studies with a focus on the orbitofrontal cortex.
authors.affiliation: Department of Computer Assisted Clinical Medicine, Medical Faculty Mannheim, Heidelberg University, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany. sebastian.domsch@medma.uni-heidelberg.de
authors.forename: Sebastian
authors.initials: S
authors.lastname: Domsch
authors.forename: Julia
authors.initials: J
authors.lastname: Linke
authors.forename: Patrick M
authors.initials: PM
authors.lastname: Heiler
authors.forename: Alexander
authors.initials: A
authors.lastname: Kroll
authors.forename: Herta
authors.initials: H
authors.lastname: Flor
authors.forename: Michèle
authors.initials: M
authors.lastname: Wessa
authors.forename: Lothar R
authors.initials: LR
authors.lastname: Schad
mesh_terms: D000328:Adult; D000465:Algorithms; D001921:Brain / Q000473:pathology; D001931:Brain Mapping / Q000379:methods*; D002540:Cerebral Cortex / Q000473:pathology; D003198:Computer Simulation; D017352:Echo-Planar Imaging / Q000379:methods; D005260:Female; D005625:Frontal Lobe / Q000473:pathology*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D015233:Models, Statistical; D009474:Neurons / Q000502:physiology; D010100:Oxygen / Q000378:metabolism; D013997:Time Factors; D055815:Young Adult
chemical_list: D010100:Oxygen