Use of personal computers and digitized film angiograms to produce subtraction angiograms.

Digitization of film angiograms for subtraction purposes alleviates many of the problems associated with conventional film subtraction techniques. In this method, conventional film angiograms are digitized with a laser digitizer. An unenhanced image is subtracted from a contrast material-enhanced image with image processing software and a personal computer. Image registration and the contrast of the subtraction mask image are adjusted as necessary to obtain complete subtractions. Subtraction images produced with this method are superior to subtraction images produced with conventional film subtraction techniques; all areas and densities of a digitized subtraction image exhibit nearly perfect subtraction. Digitized film angiograms and image processing software provide a useful alternative to traditional techniques for producing subtraction angiograms. Digital film subtraction provides more control over image registration, eliminates the need for an intermediate subtraction mask image, and allows the user to control the contrast, window width, and window level of the final image.