| SET | Singlephoton Emission Tomography = SPECT |
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| SPECT | Single Photon Emission Computed Tomography = SET |
| DLE | delayed light emission; dialyzable leukocyte extract; discoid lupus erythematosus; disseminated lupu... |
| ECT | electroconvulsive therapy; emission computed tomography; enteric coated tablet; euglobulin clot test... |
| ES | ejection sound; elastic stocking; electrical stimulus, electrical stimulation; electroshock; emergen... |
| stopping power | <radiobiology> The average rate of energy loss of a charged particle per unit thickness of a material or per unit mass of material traversed. (16 Dec 1997) |
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| independent power producer | A power production facility that is not part of a regulated utility. (05 Dec 1998) |
| firm power | (firm energy) Power which is guaranteed by the supplier to be available at all times during a period covered by a commitment. That portion of a customer's energy load for which service is assured by the utility provider. (05 Dec 1998) |
| alpha emission | <physics> Form of nuclear decay where the nucleus emits an alpha particle (see entry below). (09 Oct 1997) |
| beta emission | <radiobiology> Form of nuclear decay where a neutron splits into a proton plus electron plus neutrino set. The proton stays in the nucleus but the electron (beta ray) is ejected. (09 Oct 1997) |
| gamma emission | <physics> Nuclear decay process whereby the nucleus goes from an excited state to a more stable state by emitting a gamma ray. See: gamma ray. (09 Oct 1997) |
| particulate emission | Fine liquid or solid particles discharged with exhaust gases. Usually measured as grains per cubic foot or pounds per million Btu input. (05 Dec 1998) |
| characteristic emission | Monochromatic radiation that is produced when an electron is ejected from an atom and another takes its place by jumping from another shell; the energy of the photon is the difference between that of the two shell positions. Synonym: characteristic emission. (05 Mar 2000) |
| microscope, field emission | <microscopy> An image-forming device in which a strong electrostatic field causes cold emission of electrons from a sharply rounded point or from a specimen that has been placed on that point. The electrons are accelerated to a phosphorescent screen, or photographic film, giving a visible picture of the variation of emission over the specimen surface. (05 Aug 1998) |
| positron emission tomography | <radiology> A highly specialised research imaging technique using short lived radioactive substances - usually those made with a cyclotron. This technique is very sensitive in picking up active tumour tissue but does not measure the size of it. Tomographic images are formed by computer analysis of photons detected from annihilation of positrons emitted by radionuclides incorporated into biochemical substances; the images, often quantitated with a colour scale, show the uptake and distribution of the substances in the tissue, permitting analysis and localization of metabolic and physiological function. Because the half-lives of the radionuclides are so short (20 minutes to 2 hours), and the equipment expensive, PET is rarely used in a clinical setting. But since its development in the mid-1970s, it has proved the most important tool yet devised for experimental investigation of the living brain, whether healthy, traumatised, or diseased. With CT and MRI, it represents a new generation of computer imaging techniques that have revolutionised medicine and physiology. Acronym: PET (20 Jun 2000) |
| single photon emission computed tomography | <radiology> Tomographic imaging of metabolic and physiological functions in tissues, the image being formed by computer synthesis of photons of a single energy emitted by radionuclides administered in suitable form to the patient. The method uses radionuclides which emit a single photon of a given energy. The camera is then rotated 180 or 360 degrees around the patient to capture images at multiple positions along the arc. The computer then reconstructs the transaxial, sagittal, and coronal images from the 3-dimensional distribution of radionuclides in the target area scanned. The advantages of SPECT are that it can be used to observe biochemical and physiological processes as well as the size and volume of the organ. The disadvantage is that, unlike positron emission tomography where the positron-electron annihilation results in the emission of 2 photons at 180 degrees from each other, SPECT requires physical collimation to line up the photons, which results in the loss of available photons and hence degrades the image. Acronym: SPECT (20 Jun 2000) |
| source emission reduction plan | (SERP) A contingency plan developed to reduce emissions during an air quality emergency. (05 Dec 1998) |
| spectrometry, X-ray emission | Identification and measurement of concentration of elements based on the fact that X-rays emitted by an excited element have a wavelength characteristic of that element and an intensity related to its concentration. It includes fluorescence, or secondary-emission, X-ray spectrometry, in which the specimen is irradiated by X-rays. Primary-emission x-ray spectrometry, in which the specimen is bombarded by electrons, is a specific type of X-ray emission spectrometry known as electron probe microanalysis. (12 Dec 1998) |
| spontaneous emission | <radiobiology> Radiation randomly emitted by excited atoms or ions. Contrast with stimulated emission. (09 Oct 1997) |
| stimulated emission | <radiobiology> Radiation coherently emitted by excited ions when driven by a passing light wave and the appropriate transition wavelength. Laser means Light Amplification by Stimulated Emission of Radiation, it occurs when there is a population inversion between the upper and lower energy states of the transition, such that stimulated emission can dominate excitation. Stimulated emission is coherent and codirectional with the stimulating wave, and the rate of stimulated emission is proportional to the intensity of the stimulating wave. (09 Oct 1997) |