Science and Profession (Magill’s Medical Guide, Sixth Edition)
Nuclear medicine is the branch of medicine that uses radioactive substances in the diagnosis and treatment of diseases. A discussion of such technology requires an understanding of the nature of radioactivity and the tools employed by specialists in this medical field.
Radioactivity is the spontaneous emission of particles from the nucleus of an atom. Several kinds of emissions are possible. Gamma-ray emission is the type with which nuclear medicine imaging is concerned. The activity of radionuclides is measured in terms of the number of atoms disintegrating per unit time. The basic unit of measurement is the curie. Radiopharmaceuticals that are administered are in the microcurie or millicurie range of activity. Most radionuclides used in nuclear medicine are produced from accelerators, reactors, or generators. Accelerators are devices that accelerate charged particles (ions) to bombard a target. Cyclotron-produced radionuclides that are used frequently in nuclear medicine include gallium 67, thallium 201, and indium 111. The core of a nuclear reactor consists of material undergoing nuclear fission. Nuclides of interest in nuclear medicine that are formed from reactors include molybdenum 99, iodine 131, and xenon 133.
In generator systems, a “parent” isotope decays spontaneously to a “daughter” isotope in which the half-life of the parent is longer than that of the daughter. The parent is used to...
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Diagnostic and Treatment Techniques (Magill’s Medical Guide, Sixth Edition)
Nuclear medicine is widely used in the diagnosis and prognosis of coronary artery disease, especially in conjunction with either physical stress testing (treadmill or bicycle exercise) or pharmacological stress testing. The patient is instructed to exercise on the treadmill until his or her heart rate has significantly increased. At peak exercise, a radioisotope, usually thallium 201 or technetium 99m, is injected into a vein. Stress images are obtained. Because the injected tracer corresponds to the blood flow through the arteries that supply oxygen to the heart muscle, those vessels that have a blockage exhibit decreased flow, or decreased tracer delivered to that area of the heart. Rest images are also obtained. Rest and stress images are compared, and differences in the intensity of the tracer, analyzed by a computer, help to identify blocked arteries and the extent of the blockage. This technique is also used in follow-up of patients who have undergone bypass surgery or angioplasty to determine if blockage has recurred.
Nuclear cardiology is also used to measure the ejection fraction (the amount of blood ejected by the left ventricle to all parts of the body) and motion of the heart. Patients with cardiomyopathy, coronary artery disease, or congenital heart disease often have decreased function of the heart. Certain medications used in cancer therapy can also damage the heart muscle. These patients...
(The entire section is 1233 words.)
Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
Natural radioactivity was discovered in the late nineteenth century. The first medical success with a radioisotope was Robert Abbe’s treatment of an exophthalmic goiter with radon in 1904. In 1934, the Joliot-Curies produced artificial radioisotopes, specifically phosphorus 32. In 1938, Glenn T. Seaborg synthesized iodine 131. Phosphorus 32 was used to treat chronic leukemia and iodine 131 to treat thyroid cancer. Both treatments fell victim to radiation hysteria fueled by the aftermath of World War II and the dropping of the atomic bomb on Hiroshima. For a decade, nuclear medicine was equated with the “atomic cocktail” and was used only sporadically as a therapeutic modality. In 1949, the first gamma camera was introduced by Benjamin Cassen. It was called a “tap scanner” because as it measured radioactivity, it would tap ink on a piece of paper. The intensity of the ink mark was directly proportional to the radioactivity that was being scanned. The first nuclear medicine image was that of a thyroid gland.
Although discovered in the late 1930’s, the imaging properties of the short-lived technetium 99m were not understood until the early 1960’s. Its six-hour half-life and its chemical properties were ideally suited to imaging with the scintillation camera newly introduced in 1965. From that time on, nuclear medicine grew in its role as a diagnostic tool, with technetium agents becoming the primary...
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Brown, G. I. Invisible Rays: A History of Radioactivity. Stroud, England: Sutton, 2002. Traces the history of radioactivity with the use of biographical information on Marie Curie and other nuclear medicine pioneers.
Brucer, Marshall. A Chronology of Nuclear Medicine, 1600-1989. St. Louis, Mo.: Heritage, 1990. In an immensely enjoyable book, the author traces the history of nuclear medicine from the seventeenth century, when Robert Boyle defined a new intellectual discipline that would eventually be called “science,” through the April 28, 1986, Chernobyl nuclear accident in the Soviet Union.
Christian, Paul E., Donald Bernier, and James K. Langan, eds. Nuclear Medicine and PET: Technology and Techniques. 5th ed. St. Louis, Mo.: Mosby, 2004. A comprehensive text that encompasses the spectrum of nuclear medicine technology from basic and applied mathematics, physics, chemistry, and biology to the details of performance and principles of interpretation of individual nuclear medicine procedures, regulations, and patient care.
Iskandrian, Ami E., and Mario S. Verani, eds. Nuclear Cardiac Imaging: Principles and Applications. 4th ed. New York: Oxford University Press, 2008. Many strides have occurred in the field of nuclear cardiology since the 1970’s. These developments have had considerable impact on reshaping the entire field of cardiovascular medicine. This book...
(The entire section is 307 words.)
Nuclear Medicine (Encyclopedia of Science)
Nuclear medicine is a special field of medicine in which radioactive materials are used to conduct medical research and to diagnose (detect) and treat medical disorders. The radioactive materials used are generally called radionuclides, meaning a form of an element that is radioactive.
Radionuclides are powerful tools for diagnosing medical disorders for three reasons. First, many chemical elements tend to concentrate in one part of the body or another. As an example, nearly all of the iodine that humans consume in their diets goes to the thyroid gland. There it is used to produce hormones that control the rate at which the body functions.
Second, the radioactive form of an element behaves biologically in exactly the same way that a nonradioactive form of the element behaves. When a person ingests (takes into the body) the element iodine, for example, it makes no difference whether the iodine occurs in a radioactive or nonradioactive form. In either case, it tends to concentrate in the thyroid gland.
Third, any radioactive material spontaneously decays, breaking down into some other form with the emission of radiation. That radiation can be detected by simple, well-known means. When radioactive iodine enters the body, for example, its progress through the body can be followed with a Geiger counter or some other...
(The entire section is 819 words.)