Coincident radiation imaging of iodine 125 for in vivo gene imaging in small animals

Progress has been made towards a novel in vivo gene imaging technology which take advantage of the emission properties of 125I as the label for a gene specific probe. The radioisotope 125I decays via electron capture emitting a 35 keV γ-ray with the prompt emission of several 27–32 keV Kα and Kβ shell X-rays. Hence, a coincidence detection condition can be implemented to detect the 125I decays, thus reducing the background contribution and enhancing the possibility of detecting minute amounts of the isotope. The detector system utilizes crystal scintillators and a position-sensitive photomultiplier tube. Currently, studies in molecular biology and gene regulation follow the expression of a particular gene at a given instant in time. Presently, in situ hybridization and immunochemical assays are available to observe the spatial patterning of gene expression in an organism at any one instant in time for one organism but one must sacrifice the organism to make a measurement, essentially taking a single snap-shot of the state of expression of the gene of interest. It is hoped that this detection scheme will make possible gene imaging in live animals for extended periods of time.