Radio-imaging in small animals.

As the resolution of radio-imaging systems improves, the prospect of in-vivo imaging of small animals becomes more attractive. Purpose-built positron emission tomography (PET) scanners capable of imaging individual tissues within the rat brain are now in routine experimental use and in-vivo tracer and saturation-kinetic studies are now possible. The study of small animals in this way does have intrinsic problems and constraints associated with it. For example, the animal must be completely immobilized, stable ligand within the radiolabelled preparation may be limiting and anatomical definition may be poor. In spite of this, consistent, semi-quantitative data can be produced and in-vivo radio-imaging can provide a genuine and unique complement to more conventional techniques. Animal numbers can be significantly reduced and the quality of data improved due to reduced inter-animal variation, and longitudinal studies, to monitor disease progression, are feasible. As the resolution of imaging systems improves still further, such studies could be extended to mouse, in addition to rat, models of disease.