MEDICAL USES OF RADIOPHARMACEUTICALS

 

Uses of Technetium-99m
The radioisotope most widely used in medicine is technetium 99, employed in some 80% of all nuclear medicine procedures. It is an isotope of the artificially-produced element technetium and it has almost ideal characteristics for a nuclear medicine scan.
These are:
• It has a half-life of six hours which is long enough to examine metabolic processes yet short enough to minimise the radiation dose to the patient.
• Technetium-99m decays by a process called "isomeric"; which emits gamma rays and low energy electrons. Since there is no high energy beta emission the radiation dose to the patient is low.
• The low energy gamma rays it emits easily escape the human body and are accurately detected by a gamma camera. Once again the radiation dose to the patient is minimised.
• The chemistry of technetium is so versatile it can form tracers by being incorporated into a range of biologically-active substances to ensure that it concentrates in the tissue or organ of interest.
- Sodium pertechnetate used for Brain imaging, Cerebral angiography;thyroid imaging; salivary gland imaging; placenta localization; blood pool imaging; gastric mucosa imaging; cardiac function studies; renal blood flow studies. Urinary bladder imaging. nasolacrimal drainage system imaging.
- Sodium pertechnetate labelled red blood cells used for determine of red blood cell volume, short-term survival studies. In vitro compatibility studies.
- Tc-albuminused for blood pool imaging, cardiovascular studies, placenta localization, determine of blood or plasma volumes.
- Tc-albumin (aggregated) used for pulmonary perfusion imaging.
- Tc-albumin (microaggregated) used for Liver imaging.
- Tc-apcitideused for Acute venous thrombosis imaging.
- Tc-arcitumomab used for  tumour detection for colorectal cancer.
- Tc-bicisate used for Brain imaging.
- Tc-butedronate (DPDused for  Brain imaging.
- Tc-depreotide used for Tumour detection for lung cancer.
- Tc-disofenin (DISIDA) used for stic Hepatobiliary imaging.
- Tc-etidronate (EHDP) used for Bone imaging.
- Tc-exametazine (HM-PAO) used for Cerebral perfusion imaging.
- Tc-fanolesomab used for Imaging and diagnosis of infections.
- Tc-gluceptate: used for  Brain imaging, renal imaging, assess renal and brain perfusion.
- Tc-labeled red blood cells used for Determine of red cell volume; short-term red cell survival studies.
- Tc-lidofenin (HIDA) used for Hepatobiliary imaging.
- Tc-mebrofenin used for Hepatobiliary imaging.
- Tc-medronate (MDP) used for Bone imaging.
- Tc-mertiatide (MAG3 used for Renal imaging.
- Tc-oxidronate (HDP) used for Bone imaging.
- Tc-pentetate (DTPA) used for Brain imaging, renal imaging, assess renal and brain perfusion, estimation of glomerular filtration rate, Lung ventilation studies.
- Tc-polyphosphates used for Bone imaging, myocardial imaging, blood pool imaging, detection of gastrointestinal bleeding.
- Tc-pyrophosphate used for Bone imaging, cardiac imaging, blood pool imaging, detection of gastrointestinal bleeding.
- Tc-sestamibi (HEXAMIBI) used for myocardial perfusion imaging.
- Tc-succimer used for renal imaging.
- Tc-sulesomab used for detection of infections and inflammation.

Other Uses of Radiopharmaceuticals
Radiosynoviorthesis or radiosynovectomy is a technique wherein a radiopharmaceutical is delivered into the affected synovial compartment (the interior of joints that is lubricated by fluid) of patients suffering from joint pain, as in the case of rheumatoid arthritis. Beta-emitting radiolabelled colloids are widely used for this purpose. Several radiopharmaceuticals have been developed usingphosphorus-32, yttrium-90, samarium-153, holmium-166, erbium-169, lutetium-177, rhenium-186 etc. and some of them are registered for human use. The radiation properties of each therapeutic -isotope determine their respective use and applicability for the joint size.

Radiopharmaceuticals for Positron Emission Tomography Imaging
The  evolution of PET as a clinically useful imaging modality has its origin in the synthesis of fluorine-18 fluorodeoxyglucose (18F-FDG) in 1976 at the Brookhaven National Laboratory. Fluorine-18 is the positron emitting radioisotope. The initial application of 18F-FDG was for mapping glucose-metabolism in the brain in the understanding and monitoring neurological diseases. While it is also useful for studying myocardial viability, due to the greater utilisation of glucose by the proliferating cells, the major use of 18F-FDG subsequently emerged in the detection, staging and treatment follow-up of various types of cancers. Currently PET studies using 18F-FDG account for 10% of all imaging performed using radiopharmaceuticals. A number of other fluorine-18 labelled radiopharmaceuticals are being developed and a few of them are under clinical investigations[1]. Increasing clinical demand for 18F-FDG has triggered technological advances in various fields such as accelerator technology, radiochemistry, automated processing modules, detector systems, and imaging software. A typical cyclotron-PET centre nowadays includes a dedicated medical cyclotron together with automated radiochemistry modules and a number of PET or PET-CT units. Daily large scale production of 18F-FDG in the early morning hours for extensive and rapid distribution to medical centres is becoming common practice in several countries.

Generator produced PET Radiopharmaceuticals
The PET isotope gallium-98 can be obtained from germanium-68 – gallium-68 generator. The parent germanium-68 prepared using 30-60 MeV energy and high current cyclotron has a long half life(271 days) and hence the generator can be transported over very long distances and useful for periods of up to one year. In addition to infection imaging, gallium-68 is finding use in cancer imaging when labelled with peptides. The ultra short-lived rubidium-82 (a half-life of 75 seconds), available from astrontium-82 – rubidium-82 generator, and useful for PET imaging of blood flow to myocardium, has high potential in managing heart patients.

CONCLUSIONS
Radiopharmaceuticals in medical research care and treatment today are being used to help millions of patients throughout the world.

REFERENCES
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3. Jennifer Lilly Gutiérrez; Jennifer Gutiérrez B.S; Continuing Ed; Review of Radiopharmaceutical Use in Medicine; 2012; April 4.
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6. Chilton H.M and Witcofski R. L;  Nuclear Pharmacy,Lea & Febiger, Philadelphia; 1986.
7. Wang Y; CRC Handbook of Radioactive Nuclides;Chemical Rubber Co., Cleveland, Ohio; 1969.
8. Davey R.J and Wallace M.E; Diagnostic and Investigational Uses of Radiolabeled Blood Elements; Am. Assoc. of Blood Banks, Arlington; 1987.
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10. Freeman L.M and Blaufox M.D; Physician’s Desk Reference for Radiology and Nuclear Medicine Editorial Consultants, 5th ed, Medical Economics Co., Oradell, N.J; 1976.
11. Gennaro A.R; Remington: The Science and Practice of Pharmacy; 20th ed., Lippincott Williams & Wilkins, Baltimore, MD; 2000; 469-482.
12.  Swanson D.P et al.; Pharmaceuticals in Medical Imaging. Macmillan Publishing Co., Inc., New York, 1990.

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