Development of a small animal SPECT and CT dual function imager with a microcolumnar CsI(Tl) and CCD based detector

We report on the development of a small animal SPECT/CT dual function imager with a single detector that consists of a 300 μm thick micro-columnar structured CsI(TI) phosphor, a light image intensifier (LII), and a CCD image sensor. The detector was originally designed for x-ray micro-angiographic fluoroscopy (MAF) imaging but used here for both x-ray and gamma-ray detection in the dual function imager. The large variable gain of the LII enables the detector to meet the very different SPECT and x-ray CT sensitivity requirements. The prototype imager allowed SPECT and CT imaging on a common image-subject movement platform. A detachable 5-pinhole tungsten collimator enabled switching between the two modes. Several technology modules including projection preprocessing, imager geometrical calibration, and iterative reconstruction, were developed to generate SPECT and CT images. A 10-mm diameter rod phantom and a 25-gram mouse were scanned with the imager in both SPECT and CT modes. The images showed the expected system resolution and sensitivity performance.