Clinical molecular imaging with radiotracers: current status.

Molecular imaging is defined as the visualization, characterization, and measurement of biological processes at the molecular and cellular levels in humans and other living systems. Most clinical molecular imaging is currently done using radioisotope-labeled agents to define the activity of various metabolic pathways in vivo or to determine the distribution and density of various receptors relevant to human disease. This paper briefly reviews most of the commonly used radiopharmaceuticals in nuclear medicine, as well as newer agents that are likely to become available in the near future. The metabolic pathways include those relevant to the thyroid, parathyroid, heart, brain, bones, kidneys, liver, pancreas, adrenals and tumor. The receptor systems include agents useful in evaluating movement disorders, dementia, cardiac sympathetic enervation and neoangiogenesis. Receptor systems relevant to tumors include somatostatin receptors (neuroendocrine tumors), prostate-specific membrane antigen, carbonic anhydrase IX (renal cancer), and CD-20 (lymphoma). These agents, and newer agents that are being developed, are likely to become critical in the development of personalized medicine, where it will become increasingly important to determine whether a treatment that is targeted to a specific metabolic pathway or receptor is likely to be successful.