The two-plane angiograms are taken immediately prior to the pullback start and cover at least one heart cycle each. They are used to extract the catheter path automatically along the expected pullback trajectory by a dynamic programming approach. From the known imaging geometry, an accurate 3-D model of the catheter path within the respective vessel segment is generated for end-diastolic heart phase. For OCT acquisition, motorized pullback ensures a constant pullback speed, thus allowing to assign each OCT image frame a specific location on the 3-D catheter trajectory model. The relative and absolute orientations of the OCT frames are determined using previously reported system for establishing the absolute orientation in 3-D on IVUS images. Quantitative data can be derived from the contour data, such as luminal dimensions and plaque-cap thickness, actually considering the vessel curvature in contrast to conventional OCT reconstruction systems. The space between adjacent contours is interpolated to form a volume element. In locations of the plaque cap, integrating over an entire vessel segment or any part thereof yields the total plaque cap volume enclosed by the inner and outer cap surfaces.