Determination and evaluation of 3D biplane imaging geometries without a calibration object

Quantitative vascular analysis is useful for treatment planning and evaluation of atherosclerosis, but it requires accurate and reliable determination of the 3D vascular structures from biplane images. To facilitate vascular analysis, we have developed technique for reliable estimation of the biplane imaging geometry as well as 3D vascular structures without using a calibration phantom. The centerlines of the vessels were tracked, and bifurcation points and their hierarchy were then determined automatically. The corresponding bifurcation points in biplane images were used to obtain an estimate of the imaging geometry with the enhanced Metz-Fencil technique, starting with an initial estimate based on gantry information. This initial estimate was iteratively refined by means of non-linear optimization techniques that aligned the projections of the reconstructed 3D bifurcation points with their respective image points. Methods have also been developed for assessing the accuracy and reliability of the calculated 3D vascular centerlines. Accuracy was evaluated by comparison of distances within a physical phantom with those in the reconstructed phantom. The reliability of the calculated geometries and 3D positions were evaluated using data from multiple projections and observers.