A compact gamma camera for biological imaging

A compact detector, sized particularly for imaging a mouse, is described. The active area of the detector is approximately 46 mm x 96 mm. Two flat-panel Hamamatsu H8500 position-sensitive photomultiplier tubes (PSPMTs) are coupled to a pixellated NaI(TI) scintillator which views the animal through a copper-beryllium (CuBe) parallel-hole collimator specially designed for I-125. Although the PSPMTs have insensitive areas at their edges and there is a physical gap, corrections for scintillation light collection at the junction between the two tubes results in a uniform response across the entire rectangular area of the detector. The system described has been developed to optimize both sensitivity and resolution for in-vivo imaging of small animals injected with iodinated compounds. We demonstrate an in-vivo application of this detector, particularly to SPECT, by imaging mice injected with approximately 10-15 mu Ci of I-125.