FASTSPECT: electrical and mechanical design of a high-resolution dynamic SPECT imager

FASTSPECT is an imaging system designed for dynamic 3-D SPECT imaging of the brain. The system is based on 24 stationary modular cameras with a pinhole aperture structure having between 24 and 150 pinholes. Each camera is composed of 4 PMTs and a NaI(Tl) crystal. The original system has been replaced with a new gantry designed for use in a clinical environment. This opportunity was taken to add improved imaging capabilities. First, rotation of the aperture is now possible to acquire extra projections for static images. Second, high frame rates are obtainable by reducing dead-time between frames through distributed processing by assigning one Inmos T805 Transputer with 16 MB of RAM to each camera. Third, photomultiplier signals are now digitized to 8 bits instead of the previously used 5 bits. This additional ability allows different position-estimation schemes, including neural networks. The improved frame-rate capabilities have opened consideration of research in such areas as first-pass ventricular SPECT. Phantom studies have shown that sufficient counts can be collected in 1/20th second to reconstruct a full 3-D ventricular image. The new distributed electronics allows rapid data handling, so cardiac studies at 20 frames/sec are feasible.