Towards high performance small animal positron emission tomography

During the last decade increasingly sophisticated positron emission tomography (PET) scanners have been developed for imaging small laboratory animals. These systems often exhibit performance characteristics, e.g. spatial resolution, substantially better than contemporary human PET scanners and are often the first systems to demonstrate new technologies, e.g. avalanche photodiode-based detector modules. Despite these advances, spatial resolution, sensitivity, resolution uniformity and other performance parameters must continue to be improved if accurate general purpose imaging is to be carried out in the most popular research subject, the mouse. Moreover, as these improvements occur, methods must also be devised to minimize the resolution-degrading effects of positron range, the distance a positron travels from the decaying nucleus before encountering and mutually annihilating an electron. Range effects are particularly important for compounds labeled with "non-traditional" positron-emitters such as I-124 or Tc-94m. In order to illustrate the complex interplay of issues that must be addressed when contemplating such improvements, we describe how we have approached high performance PET imaging in the design and construction of ATLAS (Advanced Technology Laboratory Animal Scanner), a small animal PET scanner now entering service at the National Institutes of Health (NIH) in Bethesda, Md.