The authors examined the extent to which the cross-sectional shape of plexiglass coronary models, with circular, crescentic, semicircular, and double lumen cross-sectional shapes, could be characterized using only two orthogonal roentgenographic projections. Vessel models, filled homogeneously with roentgenographic contrast, were imaged with nonsimultaneous biplane digital angiography. Each vessel cross section was represented as a matrix of ones (contrast present) and zeros (contrast absent), and was reconstructed using a binary, backprojection algorithm constrained by a reconstruction of an adjacent circular reference lumen. The above single lumen cross-sectional shapes were reconstructable from biplane digital angiograms to within 17% mean error, provided appropriate a priori information was used. Double lumen cross sections, which possess an inherent ambiguity when viewed at oblique angles, were identifiable by the Euler number of their reconstructions.