CdTe Orthogonal Strip Detector for Small Animal PET

In this paper we present experimental results obtained with an orthogonal strip CdTe detector designed for application to small animal PET. The detector was designed to provide timing resolution acceptable for small animal PET, depth of interaction information and spatial resolution superior to scintillator based detectors. A CdTe sample of 20times20 mm² area and 0.5 mm thickness was patterned with strips of 0.5-mm pitch on one 20times20 mm² face. In a small animal PET detector ring the 511 keV gamma-rays would be incident on the edge of the device (i.e., 0.5times20 mm² face) and encounter 20-mm depth, providing reasonably high stopping efficiency. The strips with 0.5-mm pitch on the 20times20 mm² face (in combination with the device thickness of 0.5-mm) would provide identification of the event in an effective pixel size of 0.5times0.5 mm². The other 20times20 mm² face of the device has coarser strips with 2.0-mm width (2.5-mm pitch) in the direction orthogonal to the finer 0.5-mm strips. These 2-mm strips provide the depth of interaction (DOI) for the 511 keV gamma-rays. Since the overall thickness between the electrodes is only 0.5-mm, fast and efficient collection of electrons and holes is possible, resulting in high energy and timing resolution. Pulse height spectra under ²²Na irradiation, coincidence timing resolution and detector response to a collimated source are presented.