Ultra high resolution SPECT with CdTe for small animal imaging applications: Monte Carlo simulation study using voxelized phantom

The single photon emission computed tomography (SPECT) based on pixelated Cadmium Telluride (CdTe) detector has been promising for high resolution small animal imaging. For the feasibility of our ultra-high resolution SPECT system with CdTe, we compared the quality of the reconstructed image of our SPECT system to that of a conventional small animal SPECT system with NaI(Tl) detector. The pixel size of CdTe detector was 0.35 mm × 0.35 mm which was available for a real detector (PID350, AJAT, Finland). The detector size was 44.8 × 44.8 mm with 128 × 128 pixels and the thickness of this detector was 1 mm. The intrinsic resolution of CdTe detector and that of NaI(Tl) detector were 0.35 mm and 2.3 mm, respectively. The height parallel hole collimator made of lead was 25 mm and that of a septum was 0.2 mm. The shape of that parallel hole collimator and its radius were hexagonal and 0.5 mm, respectively. A SPECT liver scan was simulated for both SPECT with CdTe and conventional SPECT system using voxelized MOBY phantom. All SPECT images were obtained using 120 projection views acquired from 0° to 360° with a 3°. Slices were reconstructed using an Ordered Subsets Expectation Maximization (OS-EM) and 5 iterations with 4 subsets. We compared the quality of images for two systems in terms of spatial resolution (FWHM), sensitivity, signal-to-noise ratio (SNR), and contrast-to-noise (CNR). Our simulation results indicated that the reconstructed SPECT images obtained with CdTe detector showed higher resolution compared to those with the conventional scintillation detector. These results demonstrated that the SPECT imaging based on pixelated CdTe detector can improve the performance of SPECT system for small animal imaging.