Question

PET scanner comprises of large rings of scintillation detectors. With a positron- emitting radionuclide, the photopeak of the energy spectrum from this scintillation detector to have a Gaussian shape with a full-width-at-half-maximum (FWHM) equal 10% of the energy of the 511 keV gamma rays, use an energy window equivalent to the FWHM of the photopeak (centered at 511 keV) for energy discrimination in order to reject events that undergo Compton scatter in a patient (assuming a single scatter only, no multiple scatter). What is the maximum angle of scatter that will still be accepted by the detector for 511 keV gamma rays?

Answer 1

Please remember, Since cosine is symmetric with respect to angle, we could have done the same calculations for negative theta as well.