Positron emission tomography, single photon emission computed tomography and planar projection imaging of radioactive tracers have long been in use for detecting and diagnosing disease in human subjects. More recently, advanced versions of these same technologies have begun to be used across the breadth of modern biomedical research to study non-invasively small laboratory animals in a myriad of experimental settings. In this report, we describe some of the new instruments and techniques that make these measurements possible and illustrate, with a few examples, the potential power of these methods in modern biomedical research.