title: Nonlinear phase correction of navigated multi-coil diffusion images.
abstract: Cardiac pulsatility causes a nonrigid motion of the brain. In multi-shot diffusion imaging this leads to spatially varying phase changes that must be corrected. A conjugate gradient based reconstruction is presented that includes phase changes measured using two-dimensional navigator echoes, coil sensitivity information, navigator-determined weightings, and data from multiple coils and averages.A multi-shot echo planar sequence was used to image brain regions where pulsatile motion is not uniform. Reduced susceptibility artifacts were observed compared to a clinical single-shot sequence. In a higher slice, fiber directions derived from single-shot data show distortions from anatomical scans by as much as 7 mm compared to less than 2 mm for our multi-shot reconstructions. The reduced distortions imply that phase encoding can be applied in the shorter left-right direction, enabling time savings through the use of a rectangular field of view. Higher resolution diffusion imaging in the spine permits visualization of a nerve root.
authors.affiliation: Centre for Medical Image Computing, University College London, United Kingdom. D.Atkinson@ucl.uk
authors.forename: David
authors.initials: D
authors.lastname: Atkinson
authors.forename: Serena
authors.initials: S
authors.lastname: Counsell
authors.forename: Joseph V
authors.initials: JV
authors.lastname: Hajnal
authors.forename: Philip G
authors.initials: PG
authors.lastname: Batchelor
authors.forename: Derek L G
authors.initials: DL
authors.lastname: Hill
authors.forename: David J
authors.initials: DJ
authors.lastname: Larkman
mesh_terms: D000465:Algorithms; D016477:Artifacts; D001921:Brain / Q000033:anatomy & histology*; D038524:Diffusion Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D009068:Movement; D017711:Nonlinear Dynamics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity