The accuracy of image registration for the brain and the nasopharynxusing external anatomical landmarks

Abstract

We investigated the accuracy of 3D image registration using markers that arerepeatedly applied to external anatomical landmarks on the head. The purposeof this study is to establish a lower limit of the errors that would occur in,for instance, MRI-SPECT matching, which in some situations can only beachieved using external landmarks. Marker matching was compared with(single-modality) volume matching for 20 MRI scans. The results were comparedwith a published expression for the target registration error (TRE) whichgives the 3D distribution of the mismatch between both scans. It was foundthat the main error source is reapplying the external markers on theanatomical landmarks. The published expression describes the relativedistribution of the TRE in space well, but tends to underestimate the actualregistration error. This deviation is due to anisotropy in the errordistribution of the marker position (errors in the direction perpendicular tothe skin surface are in general much smaller than errors in other directions).A simulation of marker matching with anisotropy in the errors confirmed thisfinding. With four reapplied markers, the TRE is 6 mm or smaller in mostregions of the head.