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Nuclear medicine is a field of medicine that uses radioactive substances to diagnose and treat injuries and diseases, and also to understand how the body works.

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Nuclear medicine is a field of medicine that uses radioactive substances to diagnose and treat injuries and diseases, and also to understand how the body works. Radioisotopes give doctors the ability to look inside the body and observe soft tissues and organs in a manner similar to x-rays. Many radioactive materials used in nuclear medicine are gamma ray emitters – such as Iodine 131 and Technetium 99m, used for their penetrating abilities and low ionising ability. However, when ionisation of cells is required – for example, when treating some cancers, alpha emitters are often used.

The basis of nuclear medicine was discovered 100 years ago. Famous personalities such as Alexander Graham Bell suggested placing radioactive sources near tumours to treat them, and as early as 1905, radiation was used to treat thyroid disease. The 20s and 30s were times of rapid development in nuclear medicine. Radioactive phosphorus was given to animals, and their metabolic processes studied. Phosphorus-32 was also used to treat a leukaemia patient.

In 1938, technetium-99m was discovered. This radionuclide has become the basis for nuclear medicine. Because of its short 6 hour half life, low radiation dose and chemically reactive nature, it was thought to be ideal for human imaging, and is used today in about 90 percent of nuclear medicine procedures.

In the 1940s and 50s, medical cyclotrons started to appear – machines which bombard elements with high-energy particles and create new radioactive material.

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To produce such an image, a patient is given, by mouth or injection, a very small amount of a radioactive substance that chemically is drawn to different organs, bones or tissues around the body. Many organs that are not visible by other radiographic techniques become visible by using radioactive substances, which are opaque to radiation. Once the substance reaches its destination it produces an emission that is transformed into a visible image. There are two ways of doing this – in vivo, or within the patient’s body, or in vitro, analysing blood in a laboratory. Because this process uses only trace amounts of radioactivity that decays rapidly in the body – and therefore has a relatively short half-life, this detection process poses practically no danger to the patient. The amount of radiation received in a procedure like this is about the same as what is received when you have a chest x-ray.

The emissions that are given off can be identified by a number of scanners or detectors. One of these is Positron Emission Topography, or PET. It uses positron decay patterns to trace the radioactive material that has been introduces into the body. It can produce high energy 3d images that can measure and determine the structure or function of a specific organ, tumour or other metabolically active site.

How PET works-

Radioisotopes used with PETs decay by positron emission.

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Radiation therapy is based on the fact that normal tissues have a greater ability to recover from the effects of radiation than tumour cells do. A radiation dose that will destroy tumour cells will only temporarily injure adjacent normal cells.

Superficial radiation is less than 120 kilovolts and is used to treat the skin, eye and other surface cancers. Mega voltage therapy on the other hand is greater than 1000 kilovolts and used to treat tumours deep within the body.

Intense radiation exposure that is used in teletherapy, brachytherapy and all forms of radiotherapy can have side effects such as hair loss, reduced white blood cell count and nausea.

Sometimes, tumour cells are called radioresistant, in other words they are more resistant to radiation than the normal cells surrounding it. In that case, radiation therapy should not be used.

The use of nuclear technology in medicine continues to grow and develop. Researchers are currently working on new applications including the use of radioactive material to clear scarred arteries after heart surgery and to treat arthritis. Medical research using radioisotopes also are being developed to fight diseases such as Huntington’s and Alzheimer’s disease. Hopefully new developments in nuclear medicine will enable us to not only know more about the human body, but also to be able to detect and treat cancers and other diseases in the future.

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