Registration of Brain CT Images to an MRI Template for the Purpose of Lesion-Symptom Mapping

Lesion-symptom mapping is a valuable tool for exploring the relation between brain structure and function. In order to perform lesion-symptom mapping, lesion delineations made on different brain CT images need to be transformed to a standardized coordinate system. The preferred choice for this is the MNI152 template image that is based on T1-weighted MR images. This requires a multi-modal registration procedure to transform lesion delineations for each CT image to the MNI152 template image. A two-step registration procedure was implemented, using lesion-masking and contrast stretching to correctly align the soft tissue of the CT image to the MNI152 template image. The results were used to transform the lesion delineations to the template. The quality of the registration was assessed by an expert human observer. Of the 86 CT images, the registration was highly successful in 71 cases (83%). Slight manual adjustments of the lesion delineations in the standard coordinate system were required to make unsuccessful cases suitable for a lesion-symptom mapping study.