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Name: Reuben G.
Status: student
Age: 16
Location: N/A
Country: N/A
Date: 2001-2002


Question:
How does the nuclear medicine equipment work?


Replies:
Dear Reuben-

The principal business of a Nuclear Medicine department is the formation of medical images using a device called a gamma camera. Perhaps you are familiar with medical x-ray images? A gamma camera is sensitive to gamma rays. Gamma rays are very similar to x rays. They can have the same wavelengths and energies. The only difference is that x rays are produced by the acceleration of electrons whilst gamma rays are emitted from the nucleus of an unstable atom which is undergoing radioactive decay. Another important difference is that x rays pass through a patient's body and cast a shadow on a sheet of film. The light and dark areas on the film correspond to regions of different physical density in the patient's body. Bone contains denser elements than soft tissues, so bone absorbs more x rays than the soft tissues. Wherever the x rays strike the film, it turns dark. Since not many x rays pass through bone, those areas of the film do not get very dark. That is what causes light bone images to appear against a dark background on x-ray films.

In typical Nuclear Medicine imaging, a radioactive substance is injected into the patient's bloodstream. The amount of radiation is small so there is very little risk of causing harm to the patient. The substance is carefully chosen so it will concentrate in a region of disease. For example, it might be a substance that attaches to cancer cells. When the patient is placed in front of the gamma camera, an image is formed of the pattern of the radiation being emitted from the patient's body. This is different from x-ray imaging, where x rays pass through the body from an outside source. The areas where the radiation is most intense would appear to be bright on the image, and in our example this could represent the presence of cancer.

Gamma cameras contain a sheet of crystal. The atoms in the crystal absorb the gamma ray energy and, a fraction of a second later, emit some of that energy in the form of light. The electronics in the gamma camera determine the position of each flash of light. Those positions are sent to a computer which keeps track of the number of flashes detected. The areas of the image which represent the highest number of flashes will be the brightest areas. You might find it interesting to know that the official word for an image formed this way is 'radioscintigram'. 'Radio' refers to the radioactive substance, 'scinti' comes from the Latin word for 'spark', and 'gram' comes from the Greek word for 'writing'. So Nuclear Medicine imaging is literally 'writing with sparks'. I hope this helps, Reuben. For more information, check out the web site of the Society of Nuclear Medicine at http://www.snm.org or the European Association of Nuclear Medicine at http://www.eanm.org.

Best Wishes,
-JGW



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