Since the introduction of single photon emission computed tomographic (SPECT; abbreviated SPET in Europe) techniques during the 1960s,123,124 SPECT has become a routine part of virtually every nuclear medicine department. With SPECT, by moving the gamma camera or cameras around the patient and viewing the object from at least 180°, a three-dimensional (3-D) data set can be reconstructed. When this data set is reconstructed by filtered back-projection methods, the SPECT slices are viewed in the transverse, oblique, sagittal, or coronal dimensions or can be formed, by state-of-the-art systems, into a 3-D representation of the organ surface (volume “rendered”). The significance of SPECT is that out-of-plane information is removed, not simply blurred as with earlier forms of tomography in nuclear medicine and radiology.107,108,112,145