An analysis of counting losses in positron emission tomography

Positron Emission Tomography allows physicians and physiologist to view and quantify the chemical function of the human body. To facilitate this, the tomograph must be able to accurately measure the radioactivity presented to it. By making the assumption that the number of gamma rays seen by the tomograph is linearly related to the radioactivity in the field of view, the tomograph can be calibrated to make the measurement. However, since nuclear radiation occurs completely randomly, the chance that some of the gamma rays will be lost causes the measurement to be inaccurate. This research focuses on the analysis of the losses and ways to estimate the magnitude of them.

Most of the losses occur in the detector system of the tomograph. The complexity of the response of that system required that a monte carlo program be used to fully characterize that system. Three different source conditions were studied using the program and a correction scheme was devised that accurately corrected for the losses. The work was extended to block detectors.

Tradeoffs in complexity force the necessary implementation of a tomograph where multiple detectors share the same data paths. The data path reduction causes losses to occur. These losses were analyzed and suggestions made to reduce them.

Finally, three schemes to estimate the losses of the entire tomograph were investigated. Two of the three schemes performed well to the upper end of range of the tomograph.