Design and characteristics of a small animal multi-modality scanner

In a collaborative effort between the University of Virginia, Jefferson Lab, and Johns Hopkins University, we have developed a CT-SPECT scanner for small animal imaging. The scanner forms the basis of what is to be a trimodality scanner after the addition of an optical imaging component. The SPECT component of this system consists of a custom built gamma camera containing a 2 times 2 array of Hamamatsu H8500 position sensitive photomultiplier tubes coupled to a pixelated array of NaI(Tl) crystals. The detector is equipped with a pinhole collimator. The CT component consists of an X-ray source with a focal spot size of 50 microns and a Hamamatsu 7940DP-03 X-ray detector utilizing complementary metal oxide technology with a detector element size of 50 microns. Both subsystems are attached to a rotating, barrel-type gantry. Basic performance tests, including measurements of intrinsic resolution, intrinsic detector efficiency, energy resolution, and detector response uniformity for the gamma camera and measurements of the RMS dark noise, sensitivity, dynamic range, and imaging performance functions (MTF, NPS, DQE) for the X-ray camera were conducted. A CT-SPECT scan of a MicroSPECT phantom resulted in reconstructed images where the smallest details of the phantom, hot rods 1.2 mm in diameter with a center-to-center spacing of 2.4 mm, are clearly resolved. Dual modality scans of live mice were performed in order to detect the localization of PECAM-antibody tagged with Tc-99m. The scan time for CT was 6 minutes; the SPECT scan time varied from 30 minutes to 2 hours, depending on the amount of residual radioactivity in the animal