The creation and use of a positron emission tomography (PET) imaging device small enough for rats to wear is reported online this week in Nature Methods. PET is a nuclear imaging technique that uses injections of trace amounts of radiopharmaceuticals to perform whole-brain functional studies. This technology allows for whole-brain imaging of awake, freely moving rats and opens up the possibility of simultaneously assessing brain function and behavior in rodents. Although in humans it is relatively straightforward to measure behavioral and functional consequences of cognitive, pharmacologic or environmental challenges this has not been easy duplicated in rodents because they cannot ‘stay still’ inside an imaging scanner without the use of anesthetics, physical restraint or paralyzing agents. Paul Vaska and colleagues have now engineered a miniature PET scanner that rats can wear while freely moving inside a chamber. This system allows PET imaging with simultaneous collection of behavioral data and can be used in a variety of experimental challenge paradigms―such as studying sex differences between rats or how different drugs affect the brain.