Computer enhancement of direct and venous-injected left ventricular contrast angiography

Following peripheral venous injection of radiopaque contrast material, a new on-line automatic computer image enhancement technique was employed to delineate and left ventricular (LV) endocardial silhouette in 10 dogs and 8 patients. This technique employs a very fast analog-to-digital conversion system capable of digitizing video frames on-line. By averaging into digital image memory the first 30 video frames and then subtracting each incoming frame from this memory, most of the background is eliminated, leaving only the contrast-filled ventricle. Since the technique employs conventional fluoroscopic exposure rates rather than cineangiography, there is marked reduction in x-ray exposure. An in vitro study using the Rando whole body phantom demonstrated that a 5 mm object with 2% contrast could be imaged within the complex chest anatomy with an incident exposure rate of only 30 mR/sec, using digital subtraction followed by contrast enhancement. In vivo studies were performed to assess the relative accuracy of ventricular border definition using this new technique by comparison to the unenhanced images in eight patients. The difference in planimetered area of the two cardiac silhouettes was 13 +/- 4 mm2 (mean difference +/- 3.4%). In four patients both direct and peripheral venous LV angiograms were obtained. There was a small (2% to 7%) systematic difference between calculated end-diastolic and end-systolic LV volume, with peripheral venous volumes invariably being smaller. Differences in calculated ejection fraction (EF) were of smaller magnitude; the maximum absolute difference in EF was 2%. We conclude that this technique is applicable to angiographic studies involving either cardiac or peripheral vascular injection of contrast material, and allows high quality images to be obtained at approximately seven-fold reduction in radiation dose (5 mA, 65 to 85 kv).