Illustration of the main software fusion process including (A) image coregistration; (B) epicardial contour detection; (C) coronary artery segmentation; and (D) three-dimensional volume rendered fusion. Reproduced with permission from Gaemperli O, Schepis T, Kalff V, et al. Validation of a new cardiac image fusion software for three-dimensional integration of myocardial perfusion SPECT and stand-alone 64-slice CT angiography. Eur J Nucl Med Mol Imaging 2007; 34: 1097–106.