AN ALGORITHM FOR CORRECTION OF DISTORTION IN STEREOTAXIC DIGITAL SUBTRACTION ANGIOGRAPHY

An algorithm for correction of the geometrical distortion in digital s ubtraction angiography (DSA) images was developed. Originally invented for 3D X-ray angiography, the algorithm was implemented in a computer program designed to fulfil the specific needs of stereotaxic DSA. The algorithm is based on transformation of an image of a grid from a dis torted image back into its original pattern. The same transformation i s then applied pixel-by-pixel to the angiographic images, which are ac quired in direct conjunction with the grid image, without moving the g antry. The algorithm was tested in phantom studies and in the clinical situation with seven patients in ten examinations. Comparisons were m ade between co-ordinate determinations made on conventional full-size cut film and those performed on uncorrected and corrected DSA images, using 30- and 23-cm fields of view. With our method of measurement we could not show any remaining geometric distortion in the corrected DSA images. This distortion correction can, if properly applied, be used for high-precision stereotaxic DSA.