Development of a high resolution SPECT system dedicated to small animal imaging

The interest of small animal imaging has been primarily due to the recent advances in genetics with the need to perform longitudinal studies on mice or rat. Recent work has shown that single photon emission computed tomography (SPECT) imaging of small animals can provide high spatial resolution with a high sensitivity where the addition of an X-ray CT system provides the lack of anatomical structures. In our group, we are developing a multi modality system combining X-ray, SPECT and PET imaging system. In this paper, we discuss the development of the SPECT component The key features of the system are i) four individual cameras arranged around the animal, ii) one pinhole aperture and 5 detector modules per camera, iii) a 28 mm focal length, and iii) pixellated scintillator arrays of 2.3×2.3×28 mm³ VAP:Ce pixels coupled to 8×8 multi anode PMT. With the pinhole configuration, the axial field of view strongly depends on the axial size of the PMT which is 18.4 mm. In order to increase this field of view, an hybrid collimator made of parallel strip of tungsten is designed. This collimator leads to parallel collimation in the axial direction and pinhole collimation in the transverse direction. The intrinsic resolution of the system is measured to be 1.5 mm in both directions leading to a 1 mm spatial resolution in the center of the field of view using a 0.5 mm diameter pinhole aperture. The predicted absolute detection efficiency of the system is 34.9 cps/MBq and 12.9 cps/MBq for the pinhole and the hybrid collimation. As a conclusion, we propose a modular SPECT system with high spatial resolution combined with high sensitivity.