Comparison between pixel array CdTe detector and NaI(Tl) detector for ultra-high resolution small animal SPECT imaging

The single photon emission computed tomography (SPECT) based on pixelated Cadmium Telluride (CdTe) detectors has been promising for high resolution small animal imaging. For the feasibility of our CdTe detector (PID350, AJAT, Finland) in small animal SPECT system, we compared the quality of reconstructed images from our SPECT system to those from a conventional small animal SPECT system with a NaI(Tl) detector. The CdTe detector had 0.35 mm x 0.35 mm(2) pixels, which is similar to the size of the available detector (PID350, AJAT, Finland). The CdTe detector size was 44.8 x 44.8 mm(2) and the thickness of this detector was 1 mm. The size of NaI(Tl) detector was 44 mm x 96 mm2 and the thickness of this detector was 5 mm. The intrinsic spatial resolution of CdTe detector and that of NaI(Tl) detector were 0.35 mm FWHM and 2.3 mm FWHM, respectively. The parallel hole collimator of lead was 25 mm high, and the septum was 0.2 mm high. The parallel hole collimator was hexagonal with a 0.5 mm radius. The Monte Carlo simulations were performed to assess both SPECT systems. All projections were obtained using 120 projection views acquired from 0 degrees to 360 degrees with a 3 degrees step. Slices were reconstructed using an Ordered Subsets Expectation Maximization (OS-EM) with 5 iterations and 4 subsets. We compared the quality of the images from each system in terms of spatial resolution (FWHM), and sensitivity. The spatial resolution of system using CdTe and that of system using NaI(Tl) detector were 2.32 mm FWHM and 3.31mm FWHM, respectively. The system sensitivity for our SPECT with CdTe and NaI(Tl) detector were 23.22 count/sec/MBq and 54.06 count/sec/MBq, respectively. Our simulation results indicated that our SPECT with CdTe detector showed better spatial resolution compared to SPECT with NaI(Tl) detector. These results demonstrate that SPECT imaging using a pixelated CdTe detector can improve the performance of SPECT systems for small animal imaging in term of spatial resolution.