Dual modality CT/SPECT scanner for small animal imaging

This work describes the design and performance of a dual-modality system for small animal imaging combining a high spatial resolution SPECT component with an x-ray CT component. All components are mounted on a barrel type gantry which is able to rotate in 0.001 degrees increments about the animal. The SPECT subsystem consists of a four custom-built gamma cameras. The cameras can be equipped with either parallel hole or pinhole collimators depending on the study in question. The cameras can be operated in pairs to implement a unique half-cone geometry setup in order to decrease the overall acquisition time as well as maximize spatial resolution. The intrinsic spatial and energy resolutions of the gamma detectors are measured to be 1.75 mm and 17.9% respectively. Novel type of pinhole collimators was introduced. Square shape aperture with pyramid shape acceptance volume collimator was characterized both theoretically and experimentally. This type of a collimator allows for about 23% of efficiency increase without significant reduction in spatial resolution. The x-ray CT subsystem combines various interchangeable microfocus x-ray sources with either a high resolution CCD based detector or a flat panel Hamamatsu C7940 CMOS array. The CCD detector employs a 7k by 4k Phillips CCD chip with dimensions of 5 cm x 9 cm, large enough to require no minification between the gadolinium oxysulfate phosphor and the chip. The both subsystems have been installed and successfully used in phantom imaging and in a variety of small animal studies. Spatial resolutions of 50 mum for CT and 0.9 mm for SPECT have been achieved for live animal imaging. The scanner is able to obtain a lower resolution CT set in 4.5 minutes and SPECT data set in 30 minutes.