The MediSPECT Small Animal CdTe Scanner.

We present in vivo tomographic 125I imaging of a mouse thyroid carried with MediSPECT, a scanner developed at University & INFN Napoli, for SPECT studies on small animals with a small field of view (FoV) and high spatial resolution. MediSPECT is based on a fine pitch CdTe pixel detector, operating in single photon counting, (14×14 mm2, 256×256 square pixel of 55 micrometer side) and equipped with a high resolution collimators set. The scanner is composed by a gantry, hosting the collimation and detection units, rotating around a horizontal axis along which is positioned the small animal holder. The mouse has been injected with a Na125I solution with a total activity of 31.8 MBq. The planar projections for SPECT reconstruction have been acquired using a 300 m tungsten pinhole (magnification 1.47 and a FoV of 9.6×9.6 mm2). The projections have been cap-tured in a step-and shoot fashion and their SPECT reconstruc-tion has been done with a C software based on Ordered Subsets-Expectation Maximization (OS-EM) reconstruction algorithm. The spatial resolution with a 300 micrometer inhole is, in planar imaging, about 500 micrometer and, in tomographic imaging, better than 1 mm. The MediSPECT scanner has a modular structure that allows for multimodal imaging: at present, a Fluorescence Reflectance Imaging head has been installed, for planar optical imaging in addition to SPECT imaging.