Gamma camera imaging is a modern medical diagnostic technique, based to study function rather than form. The patient is injected with or inhales an appropriate drug, which became concentrated in the organ of interest. Photons emission occurs in the organ at a rate ranging spatially according to the concentration and measurements of this concentration can be made by counting emitted photons in the gamma camera. The physical and operational details of the gamma camera are described by Larsson (1980). The gamma camera rotated about an axis through the patient to collect a sequence of projections from the body at numerous equally spaced angles. The session begins with the gamma camera directly above and facing the patient. In this potion, the camera detects and records photons leaving the patient’s body in a certain time period after 20 seconds. The camera then rotates about an axis parallel to the table, stops after 64 degrees and collects counts at the new angle. This process is repeated until the gamma camera return to its original position directly above the patient. The majority of emissions are never recorded by the system since their path is not towards the camera. The camera has a lead parallel-hole collimator which further limits the number of recorded emissions by only emitted photons whose path is nearly exactly perpendicular to the surface of the camera. Figure 1 demonstrates the basic component of a gamma camera and the various paths that an emitted photon can take: (1) photon emitted away from the camera, (2) photon emitted and scattered away from the camera, (3) photon absorbed inside the subject, (4) photon emitted away from the camera but scattered through collimator, (5) photon emitted directly through the collimator, (6) photon directed towards camera, but at an angle preventing it from passing through collimator.
Detection of photons in the gamma camera: (1) photon emitted away from the camera, (2) photon emitted and scattered away from the camera, (3) photon absorbed inside the subject, (4) photon emitted away from the camera but scattered through collimator, (5) photon emitted directly through the collimator, (6) photon directed towards camera, but at an angle preventing it from passing through collimator