Development of a novel radiation imaging detector system for in vivo gene imaging in small animal studies

Many studies in molecular biology deal with following the expression and regulation of a gene at different stages of an organism´s development or under different physiological conditions. Presently in situ hybridization and immunochemical assays are available to follow the gene expression at a single moment in time for one organism. One must sacrifice the organism to make a measurement, essentially taking a snap shot of the state of expression of the gene of interest. We have made progress on a new type of gene imaging technology which takes advantage of the emission properties of the radioisotope iodine 125 (¹²⁵I) as the probe and utilizes crystal scintillators and a position sensitive photomultiplier tube. Iodine 125 decays via electron capture emitting a 35 keV gamma-ray with the prompt emission of several 27-32 keV Kα and Kβ shell X-rays. Because of this a coincidence condition can be set to detect the ¹²⁵I decays thus reducing background radiation contribution to the image. Mouse imaging studies of iodine uptake by the thyroid and melatonin receptor binding have been done with this detector system using low doses of ¹²⁵I