Abstract
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Objectives: 1. To review the biophysiological mechanisms of commonly used radiopharmaceuticals, and to use them to explain physiologic radiopharmaceutical localization patterns. 2. To present the normal distribution of commonly used radiopharmaceuticals in whole body or limited field of view studies. 3. To highlight the differences among radiopharmaceuticals with similar uptake patterns. 4. To emphasize the importance of the knowledge of normal radiopharmaceutical localization patterns to differentiate pathology from physiology.
Methods: The applicable nuclear medicine literature was reviewed in conjunction with department teaching files, to illustrate the physiologic characteristics of commonly used radiopharmaceuticals. Each was attributed the following characteristics: common uses, radioisotope half-life, radiation burden, most abundant emissions, mechanism of uptake, and normal uptake and excretion patterns. The radiopharmaceuticals surveyed included: Tc-99m pertechenetate, Tc-99m sestamibi, Tc-99m sulfur colloid, Tc-99m RBCs, Tc-99m MAA, Tc-99m DTPA, Tc-99m MDP, Tc-99m MAG3, Tc-99m DMSA, Tc-99m HMPAO WBCs, Tc-99m ECD, I-131 NaI, I-123 NaI, I-123 MIBG, Xe-133, In-111 pentetreotide, In-111 oxine WBCs, Ga-67 citrate, Tl-201 chloride, and F-18 FDG.
Results: We wanted to emphasize to the trainees that by understanding the kinetics of each radiopharmaceutical, one can easily predict the physiologic localization of most radiopharmaceuticals. Therefore, a pictorial assay of the commonly used radiopharmaceuticals was created. Each normal scan is accompanied by an explanation of the most important characteristics of the radiopharmaceutical; the differentiating features between similar tracers are stressed. The “best way to recognize” the tracer on an unlabeled image is pointed out. Conclusion: Knowledge of the mechanisms behind physiologic uptake and excretion patterns of commonly used radiopharmaceuticals allows residents in training (and technology students) to quickly identify the radiopharmaceutical used, to differentiate physiologic from pathologic uptake or artifact, and to appropriately protocol potential sequential studies.
