NONLINEAR GEOMETRIC WARPING OF THE MASK IMAGE - A NEW METHOD FOR REDUCING MISREGISTRATION ARTIFACTS IN DIGITAL SUBTRACTION ANGIOGRAPHY

Purpose: Misregistration artifact is the major cause of image degradat ion in digital subtraction angiography (DSA). The purpose of this stud y was to evaluate the efficacy of a newly developed nonlinear geometri c warping method to reduce misregistration artifact in DSA. Methods: T he processing of the images was carried out on a workstation with a fu lly automatic computerized program. After making differential images w ith a lapracian filter, 49 regions of interest (ROIs) were set in the image to be processed. Each ROI of the live image scanned the correspo nding ROI of the mask image searching for the best position to match i tself. Each pixel of the mask image was shifted individually following the data calculated from the shifts of the ROIs. Five radiologists co mpared the images produced by the conventional parallel shift techniqu e and those processed with this new method in 16 series of cerebral DS A. Results: In 14 of 16 series (88%), more radiologists judged the ima ges processed with the new method to be better in quality. Small arter ies near the skull base and veins of low density were clearly visualiz ed in the images processed by the new method. Conclusion: This newly p roposed method could be a simple and practical way to automatically re duce misregistration artifacts in DSA.