Photon Activation in Medical Physics and Tissue Elemental Analysis.
Photonuclear reactions were investigated for possible use in some areas of medical physics such as medical electron accelerators beam characterization and photon contamination of electron beams. The technique was also applied to explore its application for in vivo analysis of some tissue elements, such as N, P and O. A coincidence and a single counting system were established to monitor the yield of positron emitters generated from photonuclear (gamma,n) reactions in a high energy x-ray beam. The systems were characterized and compared at different geometrical configurations. The systems response functions were mapped in air and in a polystyrene phantom. Spectral changes in the primary photon beam from a high energy (15 MeV) medical electron accelerator have been monitored using photonuclear reactions. The beam across the radiation field was measured using Teflon cylinders and copper foils at several off-axis angles, at different source to sample distances (SSD) in air, and in solid water phantom. The experimental results were generally in agreement with Monte Carlo calculations and Schiff's theory. Photon contamination in high energy electron beams was studied using the photonuclear reaction of copper foils placed in the electron beams. The activation was performed at several off-axis angles at different electron energies. The measured angular distributions agreed with the photon angular distribution predicted by the Schiff and Lawson theories, in which the scattering foil acted as a target. A photon activation technique was used for tissue multi-elemental analysis. The major tissue elements, O, C, N, and P can be individually measured using 15 MeV and 22 MeV x-ray beams. This technique was used to measure tissue elemental composition in aging rats. The feasibility to measure total body N, P, and O, in vivo in rats was investigated.
- Pub Date:
- Biophysics: Medical; Engineering: Biomedical; Physics: Radiation; Health Sciences: Radiology