Comprehensive approach for correction of motion and distortion in diffusion‐weighted MRI

Abstract

Patient motion and image distortion induced by eddy currents cause artifacts in maps of diffusion parameters computed from diffusion-weighted (DW) images. A novel and comprehensive approach to correct for spatial misalignment of DW imaging (DWI) volumes acquired with different strengths and orientations of the diffusion sensitizing gradients is presented. This approach uses a mutual information-based registration technique and a spatial transformation model containing parameters that correct for eddy current-induced image distortion and rigid body motion in three dimensions. All parameters are optimized simultaneously for an accurate and fast solution to the registration problem. The images can also be registered to a normalized template with a single interpolation step without additional computational cost. Following registration, the signal amplitude of each DWI volume is corrected to account for size variations of the object produced by the distortion correction, and the b-matrices are properly recalculated to account for any rotation applied during registration. Both qualitative and quantitative results show that this approach produces a significant improvement of diffusion tensor imaging (DTI) data acquired in the human brain. MRI measurements of water diffusion provide important information about compositional, structural, and organizational features of biological tissues. Most clinical MRI diffusion studies are performed by acquiring single-shot echo-planar images (EPI) with diffusion sensitizing gradients of different strengths and orientations. In diffusion tensor imaging (DTI) (1), at least seven images must be acquired: one image with no diffusion sensitization, and six diffusion-weighted (DW) images with diffusion sensitization in noncollinear directions. DTI analyses, in addition to other approaches used to extract diffusion information from MRI data (2-5), require the different DW images to be spatially coregistered.Unfortunately, eddy current-induced image distortions and patient motion during prolonged acquisitions cause misalignment of the DW images. Eddy currents are significantly reduced, but not eliminated, by actively shielded gradients (6) and preemphasis correction schemes (7) in modern magnets. The methods that have been proposed to reduce residual eddy current-induced distortions in DW images are based on either field maps or images.In a field map-based correction scheme, such as that presented by Jezzard et al. (8), one measures the magnetic field produced by the eddy currents and then corrects the distortion using the field map and theoretical models of how field inhomogeneities distort the images. The major obstacle to implementation is the difficulty of rapidly acquiring reliable field maps.In an image-based registration scheme, one uses a cost function Q to measure how well the images are spatially aligned. First, a target image is chosen as a reference for all other images in the data set (source images). Because it is usually less distorted and has a higher signal-to-noise ratio (...

Development of white matter and reading skills

“…Eddy-current distortions and subject motion in the diffusion-weighted images were removed by a 14-parameter constrained nonlinear coregistration based on the expected pattern of eddy-current distortions given the phase-encode direction of the acquired data (65).…”

Correcting eddy current and motion effects by affine whole‐brain registrations: Evaluation of three‐dimensional distortions and comparison with slicewise correction

“…Most previous studies applied their EC correction scheme on phantoms or on individual subjects (14,(19)(20)(21)(22)(23)(24)(25)(26)(37)(38)(39). However, interindividual comparisons of EC distortions in a group of healthy subjects have not yet been published.…”

“…Beside the time dependence of the EC field, also secondorder, spatial EC-field components could lead to nonlinear EC distortions (20). A recent study showed that secondorder EC distortions could be of the same order of magnitude as first-order effects (40).…”

“…Rohde et al (20) presented a new registration approach for EC and motion correction, using a whole-brain transformation. They showed that the EC field induced by one diffusion gradient can be retrospectively estimated from the transformation parameters of a 14-parameter, nonlinear transformation that corrects the distortions of the corresponding DW image.…”

Thalamus segmentation based on the local diffusion direction: A group study

“…This step also compensated for motion during the DWI acquisition. The corresponding gradient directions were adapted accordingly (23)(24)(25). The tensor was then estimated from the aligned data using the "analyzedti" function from Camino (26).…”