WMH Replacement and Image Warping Evan Fletcher

Purpose of method Use warping to compile statistical profiles of WMH distributions Use warping to compile statistical profiles of WMH distributions

Goal Prevent overestimation of ventricles during warping Prevent overestimation of ventricles during warping Obtain warped image with WMH voxels outside template ventricles (not inside!) Obtain warped image with WMH voxels outside template ventricles (not inside!)

Overview of method Warp Template to T1 image Warp Template to T1 image Inverse transform WMH distribution masks onto template Inverse transform WMH distribution masks onto template Create frequency maps on template Create frequency maps on template Compare with FA images where appropriate Compare with FA images where appropriate

Steps in the Method Produce WMH mask by filtering FLAIR image Produce WMH mask by filtering FLAIR image Linearly align FLAIR to T1 subject image Linearly align FLAIR to T1 subject image Readjust WMH intensities in T1 to minimize warping errors Readjust WMH intensities in T1 to minimize warping errors Warp T1 and Template Warp T1 and Template

WMT alignment & tissue replacement

Accuracy Issues Low resolution of FLAIR images causes inaccuracies when reslicing to T1 space. Low resolution of FLAIR images causes inaccuracies when reslicing to T1 space. Partially address these by thresholding resliced image Partially address these by thresholding resliced image WMH voxels appear dark in T1 image. Estimate replacement value by local mean of white intensity WMH voxels appear dark in T1 image. Estimate replacement value by local mean of white intensity

Composite maps from warping Accurate placement of periventricular lesions warped onto template 3D view: ventricles Slice view