Multiple photon coincidence tomography.

Coincidence scanning devices that measure the distribution of radioisotopes emitting multiple photons in nuclear cascade decays offer a possible supplementary approach to tomography in nuclear medicine. Design factors that serve to determine resolution, sensitivity, and statistical noise for the multiphoton coincidence linear scanner (MCLS), the total organ kinetic imaging monitor (TOKIM), and related systems have been well studied. Focused collimator coincidence scanner (FCCS) systems are capable of extremely high resolution--spherical cold lesions of less than 0.2 cu cm volume being easily detectable. Although FCCS scan speeds are too slow for imaging of large organs, scan times for small organs or for the rescanning of suspicious or ambigous regions appearing on conventional scans are well within practical clinical limits. In view of recent developments in the on-site cyclotron production of short-lived radioisotopes and the current interest in high resolution localization of neurologic receptors in vivo, FCCS systems may prove also to be of value in basic neurophysiologic studies.