Something about the Nuclear Medicine

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Something about the Nuclear Medicine

sunnye 06-09-2009, 1:28 AM
Nuclear medicine involves the injection of a radiopharmaceutical (radioactive drug)

into a patient for either the diagnosis or treatment of disease. The history of

nuclear medicine began with the discovery of radioactivity from uranium by the

French physicist Antoine-Henri Becquerel in 1896, followed shortly thereafter by the

discovery of radium and polonium by the renowned French chemists Marie and Pierre

Curie. During the 1920s and 1930s radioactive phosphorus was administered to

animals, and for the first time it was determined that a metabolic process could be

studied in a living animal. The presence of phosphorus in the bones had been proven

using radioactive material. Soon 32P was employed for the first time to treat a

patient with leukemia. Using radioactive iodine, thyroid physiology was studied in

the late 1930s. Strontium-89, another compound that localizes in the bones and is

currently used to treat pain in patients whose cancer has spread to their bones, was

first evaluated in 1939.

A nuclide consists of any configuration of protons and neutrons. There are

approximately 1,500 nuclides, most of which are unstable and spontaneously release

energy or subatomic particles in an attempt to reach a more stable state. This

nuclear instability is the basis for the process of radioactive decay, and unstable

nuclides are termed radionuclides. During the 1940s and 1950s nuclear reactors,

accelerators, and cyclotrons began to be widely used for medical radionuclide

production. Reactor-produced radionuclides are generally electron-rich and therefore

decay by â−-emission. The main application of â−-emitters is for cancer therapy,

although some reactor-produced radionuclides are used for nuclear medicine imaging.

Cyclotron-produced radionuclides are generally prepared by bombarding a stable

target (either a solid, liquid, or gas) with protons and are therefore proton-rich,

decaying by â+-emission. These radionuclides have applications for diagnostic

imaging by positron-emission tomography (PET). One of the most convenient methods

for producing a radionuclide is by a generator. Certain parent–daughter systems

involve a long-lived parent radionuclide that decays to a short-lived daughter.

Since the parent and daughter nuclides are not isotopes of the same element,

chemical separation is possible. The long-lived parent produces a continuous supply

of the relatively short-lived daughter radionuclide and is therefore called a

generator.

Currently, the majority of radiopharmaceuticals are used for diagnostic purposes.

These involve the determination of a particular tissue's function, shape, or

position from an image of the radioactivity distribution within that tissue or at a

specific location within the body. The radiopharmaceutical localizes within certain

tissues due to its biological or physiological characteristics. The diagnosis of

disease states involves two imaging modalities: Gamma (ã) scintigraphy and PET. In

the 1950s ã scintigraphy was developed by Hal O. Anger, an electrical engineer at

Lawrence Berkeley Laboratory. It requires a radiopharmaceutical containing a

radionuclide that emits ã radiation and a ã camera or single photon emission

computed tomography (SPECT) camera capable of imaging the patient injected with the

ã-emitting radiopharmaceutical. The energy of the ã-photons is of great

importance, since most cameras are designed for particular windows of energy,

generally in the range of 100 to 250 kilo-electron volts (keV). The most widely used

radionuclide for imaging by ã scintigraphy is 99mTc (T½ = 6 hours), which is

produced from the decay of 99Mo (T½ = 66 hours). In 1959 the Brookhaven National

Laboratory (BNL) developed the 99Mo/99mTc generator, and in 1964 the first 99mTc

radiotracers were developed at the University of Chicago. The low cost and

convenience of the 99Mo/99mTc generator, as well as the ideal photon energy of 99mTc

(140 keV), are the key reasons for its widespread use. A wide variety of 99mTc

radiopharmaceuticals have been developed during the last forty years, most of them

coordination complexes. Many of these are currently used every day in hospitals

throughout the United States to aid in the diagnosis of heart disease, cancer, and

an assortment of other medical conditions.

PET was developed during the early 1970s by Michel Ter-Pogossian and his team of

researchers at Washington University. It requires a radio-pharmaceutical labeled

with a positron-emitting radionuclide (â+) and a PET camera for imaging the

patient. Positron-decay results in the emission of two 511 keV photons 180° apart.

PET scanners contain a circular array of detectors with coincidence circuits

designed to specifically detect the 511 keV photons emitted in opposite directions.

The positron-emitting radionuclides most frequently used for PET imaging are 15O (T½

= 2 minutes), 13N (T½ = 10 minutes), 11C (T½ = 20 minutes), and 18F (T½ = 110

minutes). Of these, 18F is most widely used for producing PET radiopharmaceuticals.

The most frequently used 18F-labeled radiopharmaceutical is 2-deoxy-2 [18F]fluoro-D

-glucose (FDG). This agent was approved by the Food and Drug Administration (FDA) in

the United States in 1999 and is now routinely used to image various types of cancer

as well as heart disease.

The use of radiopharmaceuticals for therapeutic applications (á- or â−-emitters)

is increasing. The first FDA-approved radiopharmaceutical in the United States was,

in fact, for therapeutic use. Sodium [131I] iodide was approved in 1951 for treating

thyroid patients. There are currently FDA-approved radiopharmaceuticals for

alleviating pain in patients whose cancer has metastasized to their bones. These

include sodium 32P-phosphate, 89Sr-chloride, and 153Sm-EDTMP (where EDTMP stands for

ethylenediaminetetramethylphosphate). In February 2002 the first radiolabeled

monoclonal antibody was approved by the FDA for the radioimmunotherapy treatment of

cancer. Yttrium-90-labeled anti-CD20 monoclonal antibody is used to treat patients

with non-Hodgkin's lymphoma.

Many branches of chemistry are involved in nuclear medicine. Nuclear chemistry has

developed accelerators and reactors for radionuclide production. Inorganic chemistry

has provided the expertise for the development of metal-based radiopharmaceuticals,

in particular, 99mTc radiopharmaceuticals, whereas organic chemistry has provided

the knowledge base for the development of PET radiopharmaceuticals labeled with 18F,

13N, 11C, and 15O. Biochemistry is involved in understanding the biological behavior

of radiopharmaceuticals, while medical doctors and pharmacists are involved in

clinical studies. Nuclear medicine, which benefits the lives of millions of people

every day, is truly a multidisciplinary effort, one in which chemistry plays a

significant role.

Re: Something about the Nuclear Medicine

methewjay 07-18-2009, 5:20 AM
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Re: Something about the Nuclear Medicine

tulipkiya 02-25-2010, 11:25 PM
Also It affects the DNA of the exposed cells, so used in cancer treatment to inhibit the DNA replication,
also used in goiter weather benign or malignant to stop the development of the thyroid and decrease the mass!!

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