Source: Dissertation Abstracts International, Volume: 62-10, Section: B, page: 4646.

Directors: John Gore; George Zubal.

A major limitation in conventional SPECT imaging is the poor sensitivity. The lead collimators used in Anger cameras allow the detection of approximately 1 out of every 10000 photons that arrive to the front face of the collimator. Consequently, to offset this disadvantage, the radiation dosage given to the patient can be considerable. It is apparent that the performance of the camera will improve if the collimator is removed. A completely redesigned camera, without the lead collimator, has been introduced, and is referred to as a Compton camera.

The Compton camera, in addition to increased sensitivity, can allow, from a single position, the simultaneous acquisition of data from multiple angular views. This reduces the possibility of artifacts due to camera motion and also eliminates the time wasted between angular positions. The increased sensitivity allows the use of lower activity levels and isotopes with shorter half-lives. The essential design of a Compton camera consists of 2 detectors. The function of the first detector is to cause and detect Compton scattered events. The material that this detector is comprised of is usually chosen from silicon (Si), germanium (Ge) or argon (Ar). The latter have high Compton scatter cross sections in the range 100--600 keV. The second detector's function is to absorb any incident radiation via the photoelectric process. Typical material choices are sodium iodide (NaI), and xenon (Xe) due to their high photo absorption cross sections.

The scope of the current thesis is to determine the optimal design and configuration of a Compton camera for use in nuclear medicine applications. This is investigated by simulating the transport of the photon flux from the source to the detectors, with the camera design serving as a constraint. The physics behind such simulation is quite complex, requiring the Boltzmann photon transport equation to be solved at every instance in the phase space. There are, however, several other unsettled issues pertaining to the design and performance of this instrument. These can be broadly classified into two categories---geometry and physics of radiation measurement. The former would include the configuration, the materials to be used and the overall shape. The latter are inherent constraints such as Doppler effects in the energy measurement, absorption and scattering (Compton and Rayleigh) processes, and gamma ray polarization issues. Unless these problems are addressed, the mechanics of the Compton camera can not be fully understood nor can its design and manufacture be optimized for clinical use.