diagnostic radiopharmaceutical, a radioactive drug administered to a patient as a diagnostic tracer to differentiate normal from abnormal anatomical structures or biochemical or physiological functions. Most diagnostic radiopharmaceuticals emit gamma rays. A collimated external gamma-ray detector can determine the concentration of the drug in different organs and produce low-resolution images of the organs. Some radiopharmaceuticals, such as those prepared with tritium, carbon-14, or phosphorus-32, do not emit gamma rays. Their diagnostic use involves analyzing the concentration of the isotope in a metabolic end product in the patient’s blood, urine, breath, or biopsy samples. For example, when glucose containing 14C is administered, the subsequent monitoring of 14CO2 in the patient’s breath can indicate the absorption of glucose, its metabolism, and its elimination as a metabolic end product.
