Videodensitometry versus digital calipers for quantitative coronary angiography. Single-plane left coronary angiograms in 18 patients were prospectively analyzed using videodensitometry (XR-70 system) and handheld digital calipers to compare arterial dimensions, stenosis dimensions, intraobserver variability and interobserver variability for the methods. A total of 648 arterial segments were measured, yielding a highly significant correlation between videodensitometry and caliper-determined cross-sectional area (r = 0.96, p = 0.0001). Similarly, a highly significant linear relation was observed between videodensitometry and caliper-determined diameter (r = 0.95, p = 0.0001). When data subsets for small, medium and large arterial segments were examined, higher variability in the correlation between videodensitometry and caliper-determined area was observed in the large segments (greater than 10 mm2). In addition, caliper-estimated areas tended to be slightly smaller than videodensitometry-estimated areas in these segments. For diameter estimations, correlations between caliper and videodensitometry data were similar for the entire range of arterial segment sizes. Intra- and interobserver variability was low for both caliper and videodensitometry determination of diameter or area. Thus, over a wide range of arterial dimensions, results obtained with caliper estimates of luminal area and diameter are comparable to those obtained with videodensitometry using the XR-70 system. 