PH 122 Lecture Notes - Single-Photon Emission Computed Tomography, Positron Emission Tomography, Bone Marrow
Document Summary
A 60 kg laboratory worker receives a whole-body x-ray exposure of 0. 50 msv. How many x-ray photons are absorbed in the worker"s body? (x rays have an rbe of 1. ) 0. 5 x 10-3 j/kg x 60 kg = 0. 03 j absorbed. 1. 3 x10. 15j / photon = 2. 3 x 1013 photons. The effects of radiation on tissue in the body depend on the susceptibility. The lining of the digestive tract is quite susceptible. Collimator allows gamma rays to penetrate only along certain lines. The paths of the allowed gamma rays intersect at the tumor. The 125i in the seeds decays to 125te, which emits low-energy x rays and gamma rays. The scan shows metabolic activity, not the bone structure. Spect scan single photon emission computed tomography. The positron annihilates with an electron to produce two oppositely directed gamma. Coincidence detection of two gamma rays means that the positron source is along that rays. line.
