Design and utility of a small animal CT/SPECT system

Recent developments in the genetic engineering of small animals have motivated us to design an in vivo dual-modality CT/SPECT system that can be used to localize and quantify uptake of single-photon radiotracers in mice. The CT system includes a 75-W x-ray tube and a CCD camera, while the radionuclide imager incorporates a CsI(TI) scintillator coupled to a Si photodiode array with interchangeable pinhole collimators. These devices are mounted on a slip-ring gantry to image a 40-mm diameter cylindrical volume, where both modalities share a common field of view without moving the table on which the animal lies horizontally. The calculated modulation transfer function of the radionuclide system exceeds 10% at 1.01p/mm. The spatial resolution of the CT system is 0.1 mm with at scan time of 15 min and a contrast resolution of 1% for soft tissue. The high-resolution CT image can be used to provide a priori information to correct both the visual quality and the quantitative accuracy of the SPECT image. This imaging system and technique is designed for in vivo functional assessments of cancer and cardiovascular disease in small animals.