Evaluation of imaging geometries calculated from biplane images.

A technique is developed that will calculate accurate and reliable imaging geometries and three-dimensional (3D) positions from biplane images of a calibration phantom. The calculated data provided by our technique will facilitate accurate 3D analysis in various clinical applications. Biplane images of a Lucite cube containing lead beads 1 mm in diameter were acquired. After identifying corresponding beads in both images and calculating their image positions, the 3D positions of the beads relative to each focal spot were determined. From these data, the transformation relating the 3D configurations were calculated to give the imaging geometry relating the biplane views. The 3D positions of objects were determined from the biplane images along with the corresponding imaging geometries. In addition, methods are developed to evaluate the quality of the calculated results on a case-by-case basis in the clinical setting. Methods are presented for evaluating the reproducibility of the calculated geometries and 3D positions, the accuracy of calculated object sizes, and the effects of errors due to time jitter, variation in user-indication, centering, and distortions on the calculated geometries and 3D reconstructions. The precision of the translation vectors and rotation matrices of the calculated geometries were within 1% and 1 degree, respectively, in phantom studies, with estimated accuracies of approximately 0.5% and 0.4 degree, respectively, in simulation studies. The precisions of the absolute 3D positions and orientations of the calculated 3D reconstructions were approximately 2 mm and 0.5 degree, respectively, in phantom studies, with estimated accuracies of approximately 1.5 mm and 0.4 degree, respectively, in simulation studies. This technique will provide accurate and precise imaging geometries as well as 3D positions from biplane images, thereby facilitating 3D analysis in various clinical applications. We believe that the study presented here is unique in that it represents the first steps toward understanding and evaluating the reliability of these 3D calculations in the clinical situation.