Initial results from a PET/planar small animal imaging system

A pair of stationary, opposed scintillation detectors in time coincidence is being used to create planar projection or tomographic images of small animals injected with positron-emitting radiotracers. The detectors are comprised of arrays of individual crystals of Bi₁₂GeO₂₀ coupled to position-sensitive photomultiplier tubes. The system uses FERA (LeCroy Research Systems) charge-sensitive ADCs and a low-cost digital I/O board as a FERA bus-to-host bridge. In projection mode, the animal is placed within the 55 mm×45 mm useful field of view of the detectors, and images are formed from coincidence lines that fall close to the normals of both detectors. In tomographic mode, the animal is placed on a rotation stage between the detectors and rotated around a vertical axis to acquire all possible lines of response. Tomographic images are then reconstructed from those lines falling within a user-specified angle of each detector normal. In mice, the system is capable 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 is currently being used to study tracer transport in normal and genetically engineered mice