Investigation of conjugate imaging using small gamma cameras

Initial investigation of the use of full field-of-view small gamma cameras as the detectors of dedicated transportable conjugate imaging systems is reported. A single 4-PMT gamma camera is used to collect conjugate data from a phantom comprising two small (0.87 cm³) hollow capsules in a water-filled cylindrical tank (800 cm³). The capsules and cylinder are filled with ^99mTc in a 14.5:1 ratio of activity concentrations. Emission and transmission images of the radioisotope-filled phantom are acquired. The transmission images, as well as flood images of the cameras, are acquired with a ^99m Tc sheet source. Data processing of the conjugate image data incorporates corrections for radioactive decay, system sensitivity, and attenuation, including correction for self-attenuation in the source. Region-of-interest analysis on the conjugate mean images results in a 6.3% overestimation of the total activity in the phantom inserts. For comparison, data are acquired also with one head of a commercial three-head camera