OBJECT: Most functional magnetic resonance imaging (fMRI) studies record the blood oxygen level-dependent (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 METHODS: Based 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. RESULTS: Using 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. CONCLUSION: The 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.
OBJECT: Most functional magnetic resonance imaging (fMRI) studies record the blood oxygen level-dependent (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 METHODS: Based 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. RESULTS: Using 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. CONCLUSION: The 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.
Authors: C Triantafyllou; R D Hoge; G Krueger; C J Wiggins; A Potthast; G C Wiggins; L L Wald Journal: Neuroimage Date: 2005-05-15 Impact factor: 6.556
Authors: Bennett A Landman; Alan J Huang; Aliya Gifford; Deepti S Vikram; Issel Anne L Lim; Jonathan A D Farrell; John A Bogovic; Jun Hua; Min Chen; Samson Jarso; Seth A Smith; Suresh Joel; Susumu Mori; James J Pekar; Peter B Barker; Jerry L Prince; Peter C M van Zijl Journal: Neuroimage Date: 2010-11-20 Impact factor: 6.556
Authors: Jochen Rick; Oliver Speck; Simon Maier; Oliver Tüscher; Olaf Dössel; Jürgen Hennig; Maxim Zaitsev Journal: MAGMA Date: 2010-05-21 Impact factor: 2.310
Authors: Francesca M Filbey; Joseph P Schacht; Ursula S Myers; Robert S Chavez; Kent E Hutchison Journal: Neuropsychopharmacology Date: 2009-12-09 Impact factor: 7.853