Distortion correction for diffusion-weighted MRI tractography and fMRI in the temporal lobes.
Single shot echo-planar imaging (EPI) sequences are currently the most commonly used sequences for diffusion-weighted imaging (DWI) and functional magnetic resonance imaging (fMRI) as they allow relatively high signal to noise with rapid acquisition time. A major drawback of EPI is the substantial geometric distortion and signal loss that can occur due to magnetic field inhomogeneities close to air-tissue boundaries. If DWI-based tractography and fMRI are to be applied to these regions, then the distortions must be accurately corrected to achieve meaningful results. We describe robust acquisition and processing methods for correcting such distortions in spin echo (SE) EPI using a variant of the reversed direction k space traversal method with a number of novel additions. We demonstrate that dual direction k space traversal with maintained diffusion-encoding gradient strength and direction results in correction of the great majority of eddy current-associated distortions in DWI, in addition to those created by variations in magnetic susceptibility. We also provide examples to demonstrate that the presence of severe distortions cannot be ignored if meaningful tractography results are desired. The distortion correction routine was applied to SE-EPI fMRI acquisitions and allowed detection of activation in the temporal lobe that had been previously found using PET but not conventional fMRI.
Imaging Science and Biomedical Engineering, School of Cancer and Imaging Sciences, University of Manchester, Manchester M13 9PT, United Kingdom. karl.embleton@manchester.ac.uk
Karl V
KV
Embleton
Hamied A
HA
Haroon
David M
DM
Morris
Matthew A Lambon
MA
Ralph
Geoff J M
GJ
Parker
D000328:Adult; D056324:Diffusion Tensor Imaging / Q000379:methods*; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation / Q000379:methods; D013702:Temporal Lobe / Q000502:physiology*; D014936:Word Association Tests; D055815:Young Adult