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Radiopharmaceuticals are radioactive compounds administered to patients for diagnosis and therapy using imaging devices like SPECT and PET scanners. These compounds consist of a radioisotope bound with a carrier molecule that targets specific organs, tissues or biochemical functions. Once administered, the distribution and fate of these compounds can be traced non-invasively using external detectors. This property enables nuclear medicine specialists to visualize normal and abnormal physiologic processes at the molecular level.
Common Radioisotopes Used
Technetium-99m is the most widely used radioisotope in radiopharmaceuticals due to its optimal nuclear characteristics. It has a short half-life of 6 hours allowing repeated scans to be performed in a single day. Other commonly used isotopes include Iodine-131, Thallium-201 and Gallium-67. Positron emitters like Fluorine-18 and Gallium-68 are favored for PET imaging due to their superior imaging properties over SPECT. Radiometals like Indium-111 and Yttrium-90 are suited for therapeutic radiopharmaceuticals given their high-energy beta emissions. Research efforts are afoot to develop targeted alpha therapy agents using Alpha particle emitting isotopes like Actinium-225 and Bismuth-213.
Radiopharmaceutical Production
Radiopharmaceuticals are produced on site at nuclear medicine departments using a medical cyclotron or radionuclide generator. Cyclotrons bombard stable isotopes like Molybdenum-98 with protons or deuterons to produce short-lived positron emitting isotopes like Flourine-18 or Gallium-68. Radionuclide generators rely on the principle of radioactive decay. For example, a Molybdenum-99/Technetium-99m generator utilizes the beta decay of parent Molybdenum-99 into daughter Technetium-99m to elute daily doses of the latter at convenience.
Radiopharmaceutical Formulation
Once the radioisotope is obtained, it is combined with the targeting biomolecule or chemical using well-established procedures. Commonly used biomolecules include monoclonal antibodies, peptides, nanobodies and nucleotides. Formulation aims to achieve high radiochemical yields and purity to ensure maximum delivery of radioactivity to target tissues. It is essential to understand the pharmacokinetics and metabolism of novel radiopharmaceuticals for translation into diagnostic and therapeutic nuclear medicine.
Clinical Applications
Bone Scintigraphy
Technetium-99m labeled diphosphonates accumulate at sites of active bone remodeling, aiding detection of fractures, infections and tumors.
Thyroid Uptake Measurement
Iodine-131 or Iodine-123 are administered to quantify thyroid function and monitor hormone therapy.
Oncological Imaging
Fluorine-18 FDG PET sensitively depicts malignancies by increased glycolytic flux. Other tracers target prostate, neuroendocrine and novel tumor targets.
Cardiology
Thallium-201 and newer agents like Tetrofosmin highlight ischemia. Radiolabeled annexin targets apoptosis during myocardial infarction evaluation.
Neurology
Various PET radiotracers visualize glucose metabolism, amyloid, dopamine and serotonin receptors opening doors to early diagnosis and monitoring disease progression/treatment response in neurological disorders.
Renal Imaging
Mercaptoacetyltriglycine (MAG3) and DTPA help evaluate renal function, obstruction and identify rare causes of hematuria.
Therapeutic Applications
Radioiodine-131 plays a pivotal role in treatment of thyroid cancer and hyperthyroidism. Yttrium-90 microspheres are administered via the hepatic artery for liver cancers. Samarium-153 and Strontium-89 help palliate painful bone metastases. Radionuclide synovectomy using Rhenium-186 or Yttrium-90 delivers radiation directly into inflamed joints for arthritis. Alpha therapeutic agents including Actinium-225 and Bismuth-213 hold promise against disseminated cancers where targeted high-linear energy transfer is desirable.
Conclusion
Radiopharmaceuticals enable the practice of molecular nuclear medicine, non-invasively visualizing physiology and pathology. Advances in radiochemistry and molecular biology underpin newly developed tracers addressing unmet clinical needs. Theranostics integrating PET imaging and targeted radionuclide therapy aims at personalized precision oncology. Adoption of artificial intelligence can help tackle “big data” to accelerate drug and tracer development. Radiopharmaceutical driven nuclear medicine will continue providing answers at the frontiers of science.
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1. Source: Coherent Market Insights, Public sources, Desk research
2. We have leveraged AI tools to mine information and compile it
