Initial results from a PET planar small animal imaging system

A pair of stationary, opposed scintillation detectors in time coincidence i s being used to create planar projection or tomographic images of small ani mals injected with positron-emitting radiotracers. The detectors are compri sed of arrays of individual crystals of bismuth germanate coupled to positi on-sensitive photomultiplier tubes. The system uses FERA (LeCroy Research S ystems) charge-sensitive ADCs and a low cost digital I/O board as a FERA bu s-to-host bridge. In projection mode, the animal is placed within the 55 mm x 45 mm useful field-of-view of the detectors and images are formed from c oincidence lines that fall close to the normals of both detectors. In tomog raphic mode, the animal is placed on a rotation stage between the detectors and rotated around a vertical axis to acquire all possible lines-of-respon se. Tomographic images are then reconstructed from those lines falling with in a user-specified angle of each detector normal. In mice, the system is c apable of high-speed, whole-body dynamic projection imaging, and whole body tomographic imaging of slowly varying tracer distributions. An ECG gating capability is also available for evaluating cardiac function. This system i s currently being used to study tracer transport in normal and genetically engineered mice.