Tracer solution
In P.E.T. medical imaging, the scanner picks up radiation from within the body and uses this to make an image. The tracer solution is a short lived radioactive liquid injected into the patient. The radioactive part of the liquid molecule is attached to a biologically active substance. This in turn is designed to move round the body and to accumulate in a specific part of the body - the part you wish to make an image from.
