Design features and performance of a CsI(Na) array based gamma camera for small animal gene research

The authors report on the development of a radiation imaging system based on a matrix of CsI(Na) scintillating crystals. This detector system has been optimized for high resolution radiation imaging of the distribution of iodine 125 (¹²⁵I) in a laboratory animal. The radioisotope ¹²⁵I is readily available as a label to molecular biology probes that can be used in gene research. Iodine 125 decays via electron capture emitting a 35 keV gamma-ray with the prompt emission of several 27-32 keV X-rays. A coincidence condition can be set to detect the ¹²⁵I decays thus reducing background radiation contribution to the image. The system utilizes the Hamamatsu 5 inch diameter 3292 position sensitive photomultiplier tube (PSPMT) coupled to the CsI(Na) matrix and a custom built high resolution copper-beryllium collimator. A conventional photomultiplier coupled to a NaI(Ti) crystal scintillator is used to detect the coincident radiation resulting from the decay of ¹²⁵I