Coronary Artery Motion Compensation in Spiral CT

摘要

Because of motion artifacts, spiral Computer Tomography (CT) is not presently a widely useful diagnostic tool in cardiac imaging. There are two time scales in CT data acquisition. The first is the time-scale of a single projection which is roughly a half millisecond. The second time-scale is that of a single rotation of the x-ray source which is about 400 ms. For diagnostic purposes, the fastest components of the heart cycle are on the order of 5 ms. Those of general interest are in the range of about 100 ms. Full-rotation CT acquisition is slower than required for freezing the cardiac motion of interest. This mismatch in speed causes motion artifacts in the reconstructed images. We focus our attention on accurately measuring lumen dimensions and on visualizing lesion architecture. This analysis requires local imaging; it does not require global motion compensation. The methods we use relate to one-dimensional motion tracking and motion compensation applied to the projection data. Dynamic programming is used for the tracking. Following the projection processing, the. CT reconstruction algorithm then acts on the motion-corrected projection data to produce the reconstructed image. In addition to applying motion compensation to the projections, we also use region-of-interest (ROI) CT reconstruction algorithms in order to utilize the locally motion-corrected projection data without generating artifacts. Those artifacts come from missing projection data that should come from outside ROI. In our case the ROI is the cross-section of the vessel being imaged.