First Results From the High-Resolution mouseSPECT Annular Scintillation Camera

Abstract

High-resolution single-photon emission computed tomography (SPECT) imaging in small animals tends to use long imaging times and large injected doses due to the poor sensitivity of single pinhole gamma cameras. To increase sensitivity while maintaining spatial resolution, we designed and constructed a multi-pinhole collimator array to replace the parallel hole collimators of a Ceraspect human SPECT brain scanner. The Ceraspect scanner is composed of an annular NaI(Tl) crystal within which the eight pinhole collimators (1-mm-diameter holes) rotate while projecting nonoverlapping images of the object onto the stationary annular crystal. In this manner, only one-eighth of a collimator rotation is required to acquire a full circle orbit tomographic data set. The imaging field of view (FOV) has a diameter of 25.6 mm in the transverse direction, which is sufficient to encompass a mouse in the transverse direction. The axial FOV is 25.6 mm at the center of the FOV and 13.9 mm at the edge of the transverse FOV. Data are currently acquired in step-and-shoot mode; however, the system is capable of list mode acquisition with the collimator continuously rotating. Images are reconstructed using a cone-beam ordered subsets expectation maximization method. The reconstructed spatial resolution of the system is 1.7 mm and the sensitivity at the center of the FOV is 13.8 cps/microCi. A whole-body bone scan of a mouse injected with [Tc-99 m]MDP clearly revealed skeletal structures such as the ribs and vertebral bodies. These preliminary results suggest that this approach is a good tradeoff between resolution and sensitivity and, with further refinement, may permit dynamic imaging in living animals.