Design of combined X-ray CT and SPECT systems for small animals

The recent development of transgenic mice has motivated the authors to design combined X-ray CT and SPECT systems for small animals. Two different systems are presented to illustrate the design considerations. The first system is based on a third generation X-ray CT with multiple pinhole SPECT using two separate detectors. The second is based on a third generation CT and converging collimator SPECT using a common detector. The first system will have spatial resolution of 0.1 and 0.75 mm for CT and SPECT, respectively, while the second will have resolution of 0.15 and 0.46 mm. Both systems will have reasonable sensitivity for animal imaging. These systems promise near perfect registration of anatomical information with the radionuclide distribution, which can assist in accurate localization of radiopharmaceutical uptake and improve absolute quantitation. These systems have applications in radiopharmaceutical development, tumor dosimetry, and nuclear cardiology.