Anatomical landmark image registration: validation and comparison

This paper describes a validation approach for (interactive) anatomical landmark registration of CT and MR images. Eleven MR-CT image pairs were used, four of which had been scanned with a Leksell stereotactic frame present. Four observers each selected twelve pairs of anatomical landmarks per image pair. The images were then registered using a least squares minimization technique, only taking six transformation parameters (translation and rotation) into account. Each observer processed all twelve image pairs five times. Secondly we describe an algorithm to automatically detect a Leksell stereotactic frame from CT and MR images, scanned according to Leksell protocol. Results have been assessed by examining observer variations in the six parameters. Observer performance is differentiated by comparing median distances (and mean deviations) of identical points in different registrations. Comparison of all results show that intra- and interobserver variations are of the same magnitude as the difference between the automatic frame registration and the average observer registration.