Variables in Radiotracer Kinetics and Biodistributions

It is possible, several hundred years later, to have some sympathy with Alfonso X when he protested the complexity of the world, even as it was perceived in the Middle Ages. If nuclear medicine practice was simple, in any given patient, the injection of a radiotracer might result in scintigraphic images that are either normal or abnormal. In the latter case disease will be present. The reality is, however, more complex and challenging. Since the tracer method reflects subtle alterations in physiology, scintigraphs may reveal not only disease but treatments, drug toxicity and medical interventions. In addition, factors in the habits and lifestyle of patients will also result in changes that may be recognized scintigraphically. In this editorial, we wish to describe some of the types of changes in radiopharmaceutical biodistributions which are due to influences other than the direct effects of disease.