Simultaneous 125I SPECT imaging of small animals with pinhole and parallel collimation

A rotating cylindrical gantry apparatus holding a pair of Hamamatsu R3292 position sensitive photomultiplier tubes (PSPMTs), each of which can include either a parallel-hole collimator or a pinhole collimator, has been used to gather planar images and single photon emission computer tomography (SPECT) data of an entire mouse. In addition, in a number of experiments a magnified view of a specific organ was obtained with pinhole collimation. The scintillators used were pixelated NaI(Tl) or CsI(Tl) with pixels 1×1×3 mm and were air coupled to the PSPMTs. The active area of each detector was a circle about 110 mm in diameter. The parallel hole detector had an intrinsic resolution in planar images of 2 mm and the pinhole collimator was used in a magnification which yielded 1 mm spatial resolution. A rigid, lightweight Lexan tube is used to contain a heated mouse bed formed in a semicylindrical shape. Warmed, humidified air as well as gas anesthetic can be introduced and exhausted via the tube. The arrangement facilitates accurate centering and positioning of the SPECT cameras to the animal. The simultaneous acquisition of whole body data and a magnified image of the gut and pancreas within the animal has been applied in a study of ¹²⁵I tagged insulin in hyperglycemic and normal mice. In a study of the effectiveness of KI blocking on uptake of iodine in a mouse thyroid, images a phantom of the thyroid and submaxillary glands were of considerable interest.