Motion Compensation and Plane Tracking for Kinematic MR-Imaging
The acquisition of time series of 3D MR images is becoming feasible nowadays, which enables the assessment of bone and soft tissue in normal and abnormal joint motion. Fast two-dimensional (2D) scanning of moving joints may also provide high temporal resolution but is limited to a single, predefined slice. Acquiring 3D time series has the advantage that after the acquisition image processing and visualization techniques can be used to reformat the images to any orientation and to reduce the through-plane motion and undesired gross motion superimposed on the relevant joint movement. In this publication, we first review such post-processing techniques for retrospective tracking of viewing planes according to a single moving rigid body (e.g. bone). Then, we present new numerical schemes for optimally tracking viewing planes according to the movement of multiple structures to compensate for their through- as well as in-plane motion. These structures can be specified in an interactive viewing program, and the motion compensated movies can be updated and displayed in real-time. The post-processing algorithms require a 4D motion-field estimation which also can be utilized to interpolate intermediate images to present the final movies in smooth cine-loops and to significantly improve the visual perceptibility of complex joint movement.
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