<title>Estimation of accuracy in localizing externally attached markers in multimodal volume head images</title>

Abstract

We recently examined the registration of multimodal volume head images using extrinsic markers. We analyzed the problem into the three separate problems of finding the positions of at least three non-collinear markers in the two images, matching corresponding markers in the two image spaces, and estimating the translation and rotation parameters of the rigid body transformation that maps one space into the other. We call the calculation of the geometric centers fiducial localization. Knowing the fiducial localization error is important since it is an important determinant of target registration error, and because it provides a useful way to compare localization algorithms. In the present work we present a technique for experimentally estimating the error associated with localizing a fiducial in a tomographic image. Our method involves acquiring a volume image of a large number of markers with precisely known positions in the physical space of a phantom containing the markers, localizing the fiducials in the image, and registering the localized fiducial positions in image space to the precisely known positions in physical space. Fiducial localization error is estimated from the fiducial registration error, i.e. the distance between corresponding fiducial positions after registration.