Radiolabelled tracers

A radiopharmaceutical consists of a pharmaceutical attached to a radionuclide that emits gamma rays. The kinetics or distribution of the radiopharmaceutical may vary from the normal because of a pathological process e.g. a malignant tumour. Biochemical changes in tumours cannot be detected by morphology. In this respect scintigra-phy, reflecting regional biochemistry, is unique compared with other imaging modalities. Anatomical and functional information are often complementary.

Several radiopharmaceuticals are used for both diagnosis and treatment; well-known examples are iodine123 and 131I which localize avidly in functioning thyroid tissue. Other simple radio-pharmaceuticals are thallium-201 (201T1) and gallium-67 ( 67Ga). The ideal radionuclide for scintigraphic imaging does not exist, but technetiuin-99m (99mTc) has many favourable characteristics.

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