Comparison of Gamma-Ray Imaging Devices with a New Three-Dimensional Phantom

Studies with point or line sources of radioactivity and of single-plane phantoms fail to characterize completely differences in imaging capacity between gamma camera devices and conventional scanners with focused collimators. Moreover, the results often fail to help the physician in the assessment of clinical scanning problems. A new three-dimensional phantom has been devised. It consists of solid rods or hollow tubes of different diameters positioned diagonally in a plastic tank. With this phantom, the imaging capacity of an instrument can be determined simultaneously at increasing depths by a single scan examination. This apparatus is a modification of a phantom originated by G.J. Hine which consisted of a radioactive line source running diagonally from top to bottom of a cube-shaped container. Radioactive tubes in the new phantom were scanned in air and in water. Inactive rods were scanned in a radioactive water background. Comparative studies with 99mTc have been completed with a 3-in. - diameter crystal scanner, a 5-in. dual-probe scanner, a ten-probe rapid scanner, an Anger camera and a Ter-Pogossian image amplifier camera. Similar studies with additional scanning devices and with other scattering media and radionuclides are in progress. So far, the Anger camera has shown the best overall imaging capacity at all depths for radioactive tubes in air and water, whereas with conventional focused collimator scanners, the tubes are visualized best only at depths within the focal planes of the collimators. The capacity to image inactive rods in a radioactive background was relatively poor for all instruments studied. However, under these conditions, the conventional 3-in. crystal scanner was most satisfactory. (author)