Dictionary:

radiation

  (rā'dē-ā'shən)

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1. The act or process of radiating: the radiation of heat and light from a fire.
2. Physics.
   1. Emission and propagation and emission of energy in the form of rays or waves.
   2. Energy radiated or transmitted as rays, waves, in the form of particles.
   3. A stream of particles or electromagnetic waves emitted by the atoms and molecules of a radioactive substance as a result of nuclear decay.
3. 1. The act of exposing or the condition of being exposed to such energy.
   2. The application of such energy, as in medical treatment.
4. Anatomy. Radial arrangement of parts, as of a group of nerve fibers connecting different areas of the brain.
5. 1. The spread of a group of organisms into new habitats.
   2. Adaptive radiation.

Definition

Radiation and radioisotopes are extensively used medications to allow physicians to image internal structures and processes in vivo (in the living body) with a minimum of invasion to the patient. Higher doses of radiation are also used as means to kill cancerous cells.

Radiation is actually a term that includes a variety of different physical phenomena. However, in essence, all these phenomena can be divided into two classes: phenomena connected with nuclear radioactive processes are one class, the so-called radioactive radiation (RR); electromagnetic radiation (EMR) may be considered as the second class.

Both classes of radiation are used in diagnoses and treatment of neurological disorders.

Description

There are three kinds of radiation useful to medical personnel: alpha, beta, and gamma radiation. Alpha radiation is a flow of alpha particles, beta radiation is a flow of electrons, and gamma radiation is electromagnetic radiation.

Radioisotopes, containing unstable combinations of protons and neutrons, are created by neutron activation. This involves the capture of a neutron by the nucleus of an atom, resulting in an excess of neutrons (neutron rich). Proton-rich radioisotopes are manufactured in cyclotrons. During radioactive decay, the nucleus of a radioisotope seeks energetic stability by emitting particles (alpha, beta, or positron) and photons (including gamma rays).

Radiation—produced by radioisotopes—allows accurate imaging of internal organs and structures. Radioactive tracers are formed from the bonding of short-lived radioisotopes with chemical compounds that, when in the body, allow the targeting of specific body regions or physiologic processes. Emitted gamma rays (photons) can be detected by gamma cameras and computer enhancement of the resulting images and allows quick and relatively noninvasive (compared to surgery) assessments of trauma or physiological impairments.

Because the density of tissues is unequal, x rays (a high frequency and energetic form of electromagnetic radiation) pass through tissues in an unequal manner. The beam passed through the body layer is recorded on special film to produce an image of internal structures. However, conventional x rays produce only a two-dimensional picture of the body structure under investigation.

Tomography (from the Greek tomos, meaning "to slice") is a method developed to allow the detailed construction of images of the target object. Initially using the x rays to scan layers of the area in question, with computer assisted tomography a computer then analyzes data of all layers to construct a 3D image of the object.

Computed tomography (also known as CT, CT scan) and computerized axial tomography (CAT) scans use x rays to produce images of anatomical structures.

Single proton (or photon) emission computed tomography (SPECT) produces three-dimensional images of an organ or body system. SPECT detects the presence and course of a radioactive substance that is injected, ingested, or inhaled. In neurology, a SPECT scan can allow physicians to examine and observe the cerebral circulation. SPECT produces images of the target region by detecting the presence and location of a radioactive isotope. The photon emissions of the radioactive compound containing the isotope can be detected in a manner that is similar to the detection of x rays in computed tomography (CT). At the end of the SPECT scan, the stored information can be integrated to produce a computer-generated composite image.

Positron emission tomography (PET) scans utilize isotopes produced in a cyclotron. Positron-emitting radionuclides are injected and allowed to accumulate in the target tissue or organ. As the radionuclide decays, it emits a positron that collides with nearby electrons to result in the emission of two identifiable gamma photons. PET scans use rings of detectors that surround the patient to track the movements and concentrations of radioactive tracers. PET scans have attracted the interest of physicians because of their potential use in research into metabolic changes associated with mental diseases such as schizophrenia and depression. PET scans are used in the diagnosis and characterizations of certain cancers and heart disease, as well as clinical studies of the brain. PET uses radio-labeled tracers, including deoxyglucose, which is chemically similar to glucose and is used to assess metabolic rate in tissues and to image tumors, and dopa, within the brain.

Electromagnetic radiation

In contrast to imaging produced through the emission and collection of nuclear radiation (e.g., x rays, CT scans), magnetic resonance imaging (MRI) scanners rely on the emission and detection of electromagnetic radiation.

Electromagnetic radiation results from oscillations of components of electric and magnetic fields. In the simplest cases, these oscillations occur with definite frequency (the unit of frequency measurement is 1 Hertz (Hz), which is one oscillation per second). Arising in some point (under the action of the radiation source), electromagnetic radiation travels with the velocity that is equal to the velocity of the light, and this velocity is equal for all frequencies. Another quantity, wavelength, is often used for the description of electromagnetic radiation (this quantity is similar to the distance between two neighbor crests of waves spreading on a water surface, which appear after dropping a stone on the surface). Because the product of the wavelength and frequency must equal the velocity of light, the greater the wave frequency, the less its wavelength.

MRI scanners rely on the principles of atomic nuclear-spin resonance. Using strong magnetic fields and radio waves, MRIs collect and correlate deflections caused by atoms into images. MRIs allow physicians to see internal structures with great detail and also allow earlier and more accurate diagnosis of disorders.

MRI technology was developed from nuclear magnetic resonance (NMR) technology. Groups of nuclei brought into resonance, that is, nuclei absorbing and emitting photons of similar electromagnetic radiation such as radio waves, make subtle yet distinguishable changes when the resonance is forced to change by altering the energy of impacting photons. The speed and extent of the resonance changes permit a non-destructive (because of the use of low-energy photons) determination of anatomical structures.

MRI images do not utilize potentially harmful ionizing radiation generated by three-dimensional x-ray CT scans, but rely on the atomic properties (nuclear resonance) of protons in tissues when they are scanned with radio frequency radiation. The protons in the tissues, which resonate at slightly different frequencies, produce a signal that a computer uses to tell one tissue from another. MRI provides detailed three-dimensional soft tissue images.

These methods are used successfully for brain investigations.

Radiation therapy (radiotherapy)

Radiotherapy requires the use of radioisotopes and higher doses of radiation that are used diagnostically to treat some cancers (including brain cancer) and other medical conditions that require destruction of harmful cells.

Radiation therapy is delivered via external radiation or via internal radiation therapy (the implantation/injection of radioactive substances).

Cancer, tumors, and other rapidly dividing cells are usually sensitive to damage by radiation. The goal of radiation therapy is to deliver the minimally sufficient dosage to kill cancerous cells or to keep them from dividing. Cancer cells divide and grow at rates more rapid than normal cells and so are particularly susceptible to radiation. Accordingly, some cancerous growths can be restricted or eliminated by radioisotope irradiation. The most common forms of external radiation therapy use gamma and x rays. During the last half of the twentieth century, the radioisotope cobalt-60 was the frequently used source of radiation used in such treatments. More modern methods of irradiation include the production of x rays from linear accelerators.

Iodine-131, phosphorus-32 are commonly used in radiotherapy. More radical uses of radioisotopes include the use of boron-10 to specifically attack tumor cells. Boron-10 concentrates in tumor cells and is then subjected to neutron beams that result in highly energetic alpha particles that are lethal to the tumor tissue.

Precautions

Radiation therapy is not without risk to healthy tissue and to persons on the health care team, and precautions (shielding and limiting exposure) are taken to minimize exposure to other areas of the patient's body and to personnel on the treatment team.

Therapeutic radiologists, radiation oncologists, and a number of technical specialists use radiation and other methods to treat patients who have cancer or other tumors.

Care is taken in the selection of the appropriate radioactive isotope. Ideally, the radioactive compound loses its radioactive potency rapidly (this is expressed as the half-life of a compound). For example, gamma-emitting compounds used in SPECT scans can have a half-life of just a few hours. This is beneficial for the patients, as it limits the contact time with the potentially damaging radioisotope.

The selection of radioisotopes for medical use is governed by several important considerations involving dosage and half-life. Radioisotopes must be administered in sufficient dosages so that emitted radiation is present in sufficient quantity to be measured. Ideally the radioisotope has a short enough half-life that, at the delivered dosage, there is insignificant residual radiation following the desired length of exposure.

New areas of radiation therapy that may prove more effective in treating brain tumors (and other forms of cancers) include three-dimensional conformal radiation therapy (a process where multiple beans are shaped to match the contour of the tumor) and stereotactic radiosurgery (used to irradiate certain brain tumors and obstructions of the cerebral circulation). Gamma knives use focused beams (with the patient often wearing a special helmet to help focus the beams), while cyberknifes use hundreds of precise pinpoint beams emanating from a source of irradiation that moves around the patient's head.

Resources

BOOKS

Saha, Gopal B. Fundamentals of Nuclear Pharmacy. New York: Springer-Verlag, 1999.

WEBSITES

Society of Nuclear Medicine. "What Is Nuclear Medicine?" May 12, 2004 (May 27, 2004). http://www.snm.org/nuclear/index.html.

Alexander Ioffe

The emission and propagation of energy; also, the emitted energy itself. The etymology of the word implies that the energy propagates rectilinearly, and in a limited sense, this holds for the many different types of radiation encountered.

The major types of radiation may be described as electromagnetic, acoustic, and particle, and within these major divisions there are many subdivisions. Electromagnetic radiation is classified roughly in order of decreasing wavelength as radio, microwave, visible, ultraviolet, x-rays, and γ-rays. Acoustic or sound radiation may be classified by frequency as infrasonic, sonic, or ultrasonic in order of increasing frequency, with sonic being between about 16 and 20,000 Hz. The traditional examples of particle radiation are the α‐ and β-rays of radioactivity. See also Electromagnetic radiation; Radioactivity; Sound.

1. the process of emitting radiant energy in the form of waves or particles. n 2. the combined processes of emission, transmission, and absorption of radiant energy.

Radiation. (Bird/Robinson, 2002)

ܖrādēˈā˜ǝn n. 1. the emission of energy as electromagnetic waves or as moving subatomic particles, especially high-energy particles that cause ionization.

2. the energy transmitted in this way: background radiation | the radiation dose.

See the Introduction, Abbreviations and Pronunciation for further details.

Energy travelling in the form of electromagnetic waves. These may be X-rays, ultraviolet, visible, infra-red, microwaves, or radio waves.

For more information on radiation, visit Britannica.com.

The transmission of heat through space by means of electromagnetic waves; the heat energy passes through the air between the source and the heated body without heating the intervening air appreciably.

The emission or transfer of radiant energy (e.g. heat) as rays, electromagnetic waves, or particles. At rest, radiation is the main method of dissipating body heat. A nude body loses about 60% of its excess heat by radiation.

Energy sent out in the form of particles or waves. (See alpha radiation, beta radiation, blackbody, cosmic rays, electromagnetic radiation, fluorescence, gamma radiation, photon, and quanta.)

1. divergence from a common center.
2. a structure made up of diverging elements, especially a tract of the central nervous system made up of diverging fibers.
3. energy carried by waves or a stream of particles. One type is electromagnetic radiation, which consists of wave motion of electric and magnetic fields. The quantum theory is based on the fact that electromagnetic waves consist of discrete particles, called photons, that have an energy inversely proportional to the wavelength of the wave. In order of increasing photon energy and decreasing wavelength, the electromagnetic spectrum is divided into radio waves, infrared light, visible light, ultraviolet light and x-rays.
Another type is the radiation emitted by radioactive materials. Alpha particles are high-energy helium-4 nuclei consisting of two protons and two neutrons, which are emitted by radioisotopes of heavy elements, such as uranium. Beta particles are high-energy electrons, which are emitted by radioisotopes of lighter elements. Gamma rays are high-energy photons, which are emitted along with alpha and beta particles and are also emitted alone by metastable radionuclides, such as technetium-99m. Gamma rays have energies in the x-ray region of the spectrum and differ from x-rays only in that they are produced by radioactive decay rather than by x-ray machines.
Radiation with enough energy to knock electrons out of atoms and produce ions is called ionizing radiation. This includes alpha and beta particles and x-rays and gamma rays.

• r. biology — study of the effects of ionizing radiation on living tissues.
• corpuscular r. — particles emitted in nuclear disintegration, including alpha and beta particles, protons, neutrons, positrons and deuterons.
• r. detection — special equipment, including Geiger–Müller tubes and a scintillation crystal, is available to detect radiation which may be accidental, or detect small amounts where this is expected but it needs to be measured in terms of accumulated dose.
• electromagnetic r. — energy, unassociated with matter, that is transmitted through space by means of waves (electromagnetic waves) traveling in all instances at 3 × 10¹⁰ cm or 186,284 miles per second, but ranging in length from 10¹¹ cm (electrical waves) to 10⁻¹² cm (cosmic rays) and including radio waves, infrared, visible light and ultraviolet, x-rays and gamma rays.
• r. exposure — means more than the patient being exposed intentionally to an x-ray beam. Technical persons in the vicinity will also be exposed to a much less dangerous but perniciously cumulative load of radiation.
• infrared r. — the portion of the spectrum of electromagnetic radiation of wavelengths ranging between 0.75 and 1000 μm. See also infrared.
• r. injury — is caused by exposure to radioactive material. High doses cause intense diarrhea and dehydration and extensive skin necrosis. Median doses cause initial anorexia, lethargy and vomiting then normality for several weeks followed by vomiting, nasal discharge, dysentery, recumbency, septicemia and a profound pancytopenia. Death is the most common outcome. Chronic doses cause cataract in a few. Congenital defects occur rarely.
• interstitial r. — energy emitted by radium or radon inserted directly into the tissue.
• ionizing r. — corpuscular or electromagnetic radiation that is capable of producing ions, directly or indirectly, in its passage through matter. Used in treatment of radiosensitive cancer, in sterilization of animal products and food for experimental use.
• r. necrosis — see radionecrosis.
• r. physicist — the person responsible for the administration of radiation therapy including estimating the dose required for a treatment, arranging for the dose to be delivered and making arrangements for safety of the patient and staff, and disposing of any residual radioactive material. Technical aspects of the work include computer estimations, preparation of isodose curves, preparation of wedge and compensating filters, and calibration of teletherapy equipment.
• primary r. — radiation emanating from the x-ray tube which is absorbed by the subject or passes on through the subject without any change in photon energy.
• r. protection — includes proper control of emissions from the x-ray machines, proper protective clothing for staff, keeping unnecessary people out of the way while the tube is actually generating its beam, the wearing and regular examination of a dosimeter and the proper storage of radioactive materials or residues.
• pyramidal r. — fibers extending from the pyramidal tract to the cortex.
• r. sensitivity — tissues vary in their sensitivity to the damaging effects of irradiation. The rapidly growing tissues are most susceptible, e.g. the embryo, rapidly growing cancer, gonads, alimentary tract, skin and blood-forming organs.
• r. sickness — see radiation injury (above).
• solar r. — see solar.
• r. striothalamica — a fiber system joining the thalamus and the hypothalamic region.
• tegmental r. — fibers radiating laterally from the nucleus ruber.
• thalamic r. — fibers streaming out through the lateral surface of the thalamus, through the internal capsule to the cerebral cortex.
• r. therapist — a person skilled in radiotherapy. See also radiation therapy (below).
• r. therapy — see radiotherapy.
• ultraviolet r. — the portion of the spectrum of electromagnetic radiation of wavelengths ranging between 0.39 and 0.18 μm. See also ultraviolet rays.

Radiation as used in physics, is energy in the form of waves or moving subatomic particles. Radiation can be classified as ionizing or non-ionizing radiation, depending on its effect on atomic matter. The most common use of the word "radiation" refers to ionizing radiation. Ionizing radiation has enough energy to ionize atoms or molecules while non-ionizing radiation does not. Radioactive material is a physical material that emits ionizing radiation.

This shows three different types of radiation and their penetration levels

Types of Radiation

• Electromagnetic radiation: (Energy in the form of electromagnetic waves or photons.)
  • Non-ionizing
    • Thermal radiation (heat radiation)
    • Radio waves
    • Microwave radiation, as used in microwave ovens
    • Infrared radiation (IR), produced by heat
    • Visible light light that is visible to the naked eye
    • Ultraviolet radiation (UV) is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays.
  • Ionizing
    • X-rays, used in radiography for medical diagnosis
    • Gamma radiation, usually emitted by radioactive atoms
• Particle radiation: (Energy in the form of moving subatomic particles.)
  • Alpha radiation, composed of the nuclei of helium-4 atoms
  • Beta radiation, consisting of energetic electrons or positrons
  • Neutron radiation, consisting of neutrons

The effect of magnetic and electric fields on these particles/rays:

• Positively charged alpha particles are deflected by both magnetic and electric fields.
• Negatively charged beta particles are also deflected by both types of fields, but in the opposite direction from alpha particles.
• Neutrons and electromagnetic radiation have no charge, and are unaffected by electromagnetic fields.

See also

• Background radiation, which actually refers to the background ionizing radiation
• Cosmic microwave background radiation, 3K blackbody radiation that fills the Universe
• Radiant energy, radiation emitted by a source into the surrounding environment.
• Radiation damage - adverse effects on materials and devices
• Radiation hormesis - dosage threshold damage theory
• Radiation poisoning - adverse effects on life forms
• Radiation hardening - making devices resistant to failure in high radiation environments
• Radioactive contamination
• Radioactive decay
• Hawking radiation
• Cherenkov radiation
• Cyclotron radiation
• Synchrotron radiation
• Radiation reaction

This entry is from Wikipedia, the leading user-contributed encyclopedia. It may not have been reviewed by professional editors (see full disclaimer)

Dansk (Danish)
n. - stråling, udstråling

idioms:

• radiation sickness    strålesyge, strålingssyge

Nederlands (Dutch)
straling, uitstraling, bestraling (medische behandeling), radiale ordening

Français (French)
n. - (Méd, Nucl) radiation, (Phys) rayonnement

idioms:

• radiation sickness    mal des rayons

Deutsch (German)
n. - Strahlung, Ausstrahlung

idioms:

• radiation sickness    (Med.) Strahlungskrankheit

Ελληνική (Greek)
n. - (φυσ.) ακτινοβολία, ραδιενέργεια

idioms:

• radiation sickness    προσβολή από ραδιενέργεια

Italiano (Italian)
radiazione

idioms:

• radiation sickness    malattia da radiazioni

Português (Portuguese)
n. - radiação (f), irradiação (f)

idioms:

• radiation sickness    doença causada pela radiação

Русский (Russian)
радиация, излучение

idioms:

• radiation sickness    лучевая болезнь

Español (Spanish)
n. - radiación

idioms:

• radiation sickness    radiotoxemia

Svenska (Swedish)
n. - strålning

中文（简体） (Chinese (Simplified))
发光, 辐射, 发热, 辐射能

idioms:

• radiation sickness    辐射病

中文（繁體） (Chinese (Traditional))
n. - 發光, 輻射, 發熱, 輻射能

idioms:

• radiation sickness    輻射病

한국어 (Korean)
n. - 발광, 복사 , 방사, 빛, 열

日本語 (Japanese)
n. - 発光, 放射, 輻射, 放射物

idioms:

• radiation sickness    放射線病, 放射線宿酔

العربيه (Arabic)
‏(الاسم) اشعاع‏

עברית (Hebrew)
n. - ‮קרינה, רדיואקטיביות‬

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