Energy Resolution

A 0.22-MBq ⁶⁸Ge cylindric source (Eckert and Ziegler Isotope Products) with a diameter of 37 mm and a length of 100 mm was placed at the center of the field of view (CFOV) of the PET subsystem to acquire a 2-dimensional flood irradiation for each detector module. A semiautomated program defined the crystal look-up tables that classify regions in the flood image into the proper crystal of the scintillator array. Energy spectra of individual crystals were extracted on the basis of the look-up tables, and a gaussian function was fitted to the photopeak of each energy spectrum. Energy resolution was measured for every crystal in the scanner as the full width at half maximum (FWHM) of the gaussian function divided by the energy corresponding to the center of the photopeak, expressed as a percentage.