3D-localization of anatomic structures in tomographic images from optical flow of projection images

摘要

Optical flow-based methods are commonly used to detect and correct patient motion in modalities such as cone-beam computed tomography. With such methods, the rotational motion deriving from the acquisition trajectory itself is obscuring the patient motion and therefore considered a perturbation. In this work, the question commonly posed in motion estimation is reversed. Instead of considering the rotational motion as obscuring the patient motion, it can be used to derive shape information about the patient. This is done by computing the optical flow from projection images in order to find point correspondences in different frames of the acquisition. Finally, projective geometry is used to localize a given pair of corresponding 2D image points in 3D object space.The advantage of this method is that it allows for the localization of structures which are not contained within the scan field of view of truncated acquisitions but within an extended projection field of view. Therefore, it is shown that for certain high contrast structures, e.g. the skull, this localization method can be used to estimate the maximum extent of a patient from truncated projection data, which is an important information for extrapolation methods, or to localize highly absorbing structures outside of the scan field of view which contribute to the severity of the typically observed truncation artifacts.