['The aim of this study was to compare lesion dimensions as determined by a three-dimensional quantitative coronary angiographic (QCA) system to that of a validated two-dimensional QCA system.', 'In an era of drug-eluting stents, device sizing has become an important clinical application of online QCA. The CardiOp-B system integrates two standard angiographic projections to provide a three-dimensional reconstruction of the arterial segment of interest.', 'Phase 1 - 47 stenoses from consecutive coronary angiograms were assessed in two projections with both systems providing two data sets for the CMS-Medis system and a single data set for CardiOp-B. Phase 2--a perspex phantom with a known lesion length, was analyzed at increasing degrees of foreshortening with acceptance criteria set at 5% from the absolute value.', 'Phase 1 demonstrated an adequate correlation between the CardiOp-B and Medis systems when minimal luminal diameter was measured in the optimal view (1.32 +/- 0.47 mm vs 1.42 +/- 0.49 mm respectively; r = 0.82). A stronger correlation was noted when length was measured (25.27 +/- 10.76 mm and 21.32 +/- 8.08 mm, respectively; r = 0.95); however CardiOp-B provided a consistently longer length (P < 0.0001). On phantom length measurements the mean accuracy result for the CardiOp-B system was -1.3%. This compared favorably with the two-dimensional system where all measures performed at greater than 20 degrees of for shortening were beyond the 5% criteria from the known length.'] Do three-dimensional vessel analyses provide more accurate length estimations than the gold standard QCA?