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Encyclopedia > Gamma camera
Diagrammatic cross section of a gamma camera detector
Diagrammatic cross section of a gamma camera detector

A gamma camera is an imaging device, most commonly used as a medical imaging device in nuclear medicine. It produces images of the distribution of gamma ray emitting radionuclides. Image File history File links Gamma_camera_cross_section. ... Image File history File links Gamma_camera_cross_section. ... Nuclear medicine is a branch of medicine and medical imaging that uses unsealed radioactive substances in diagnosis and therapy. ... This article is about electromagnetic radiation. ... A radionuclide is an atom with an unstable nucleus. ...


A gamma camera is a complex device consisting of one or more detectors mounted on a gantry. It is connected to an acquisition system for operating the camera and for storing the images.


The system accumulates counts of gamma photons that are absorbed by a crystal in the camera, usually a large flat crystal of sodium iodide with thallium doping in a light-sealed housing. The crystal scintillates in response to incident gamma radiation: when the energy of an absorbed gamma photon is released, a faint flash of light is produced. This phenomenon is similar to the photoelectric effect. Photomultiplier tubes (PMT) behind the crystal detect the fluorescent flashes and a computer sums the fluorescent counts. The computer in turn constructs and displays a two dimensional image of the relative spatial count density on a monitor. This image then reflects the distribution and relative concentration of radioactive tracer elements present in the organs and tissues imaged. This article is about electromagnetic radiation. ... In physics, the photon (from Greek φως, phōs, meaning light) is the quantum of the electromagnetic field; for instance, light. ... Scintillation is a flash of light produced in a transparent material by an ionizing event. ... The photoelectric effect is the emission of electrons from matter upon the absorption of electromagnetic radiation, such as ultraviolet radiation or x-rays. ... Photomultipliers, or photomultiplier tubes (PMT) are extremely sensitive detectors of light in the ultraviolet, visible and near infrared. ...


Hal Anger developed the first gamma camera in 1957. His original design, frequently called the Anger camera, is still widely used today. The Anger camera uses sets of vacuum tube photomultipliers. Generally each tube has an exposed face of about 3 inches in diameter and the tubes are arranged in hexagon configurations, behind the absorbing crystal. The electronic circuit connecting the photodetectors is wired so as to reflect the relative coincidence of light fluorescence as sensed by the members of the hexagon detector array; all the PMTs which simultaneously detect the (presumed) same flash of light. Thus the spatial location of each single flash of fluorescence is reflected as a pattern of voltages within the interconnecting circuit array. Hal Oscar Anger (born 1920 in Denver, Colorado, USA) was an electrical engineer and biophysicist at Donner Laboratory, UCB. In 1957, he invented the scintillation camera, known also as the gamma camera or Anger camera. ... 1957 (MCMLVII) was a common year starting on Tuesday of the Gregorian calendar. ... In electronics, a vacuum tube (U.S. and Canadian English) or (thermionic) valve (outside North America) is a device generally used to amplify, or otherwise modify, a signal by controlling the movement of electrons in an evacuated space. ...


In order to obtain spatial information about the gamma emissions from an imaging subject (e.g. a person's heart muscle cells which have absorbed an intravenous injected radioactive, usually thallium-201 or technetium-99, medicinal imaging agent) a method of correlating the detected photons with their point of origin is required. Gamma (uppercase Γ, lowercase γ) is the third letter of the Greek alphabet. ...


The conventional method is to place a collimator over the detection crystal/PMT array. The collimator essentially consists of a thick sheet of lead, typically 1-3 inches thick, with thousands of adjacent holes through it. The individual holes limit photons which can be detected by the crystal to a cone; the point of the cone is at the midline center of any given hole and extends from the collimator surface outward. However, the collimator is also one of the sources of blurring within the image; lead does not totally attenuate incident gamma photons, there can be some crosstalk between holes. How a lead collimator filters a stream of rays. ... General Name, Symbol, Number lead, Pb, 82 Chemical series poor metals Group, Period, Block 14, 6, p Appearance bluish white Atomic mass 207. ... In telecommunication, the term crosstalk (XT) has the following meanings: 1. ...


Unlike a lens, as used in visible light cameras, the collimator attenuates most (>99%) of incident photons and thus greatly limits the sensitivity of the camera system. Large amounts of radiation must be present so as to provide enough exposure for the camera system to detect sufficient scintillation dots to form a picture.


Other methods of image localization (pinhole, rotating slat collimator with CZT (Gagnon & Matthews) and others) have been proposed and tested; however, none have entered widespread routine clinical use. Principle of a pinhole camera. ... Cadmium zinc telluride, or CZT, is (as the name indicates) a compound of cadmium, zinc and tellurium. ...


The best current camera system designs can differentiate two separate point sources of gamma photons located a minimum of 1.8 cm apart, at 5 cm away from the camera face. Spatial resolution decreases rapidly at increasing distances from the camera face. This limits the spatial accuracy of the computer image: it is a fuzzy image made up of many dots of detected but not precisely located scintillation. This is a major limitation for heart muscle imaging systems; the thickest normal heart muscle in the left ventricle is about 1.2 cm and most of the left ventricle muscle is about 0.8 cm, always moving and much of it beyond 5 cm from the collimator face. To help compensate, better imaging systems limit scintillation counting to a portion of the heart contraction cycle, called gating, however this further limits system sensitivity.


SPECT cardiac imaging, as used in nuclear cardiac stress testing, is performed using Anger cameras, usually one, two or three of which are slowly turned in a circle, on a single axis of rotation, around the target. SPECT (Single Photon Emission Computed Tomography) is a nuclear medicine tomographic imaging technique using gamma rays. ... A cardiac stress test is a medical test performed to evaluate relative arterial blood flow increases to the left ventricular heart muscle during exercise, as compared to resting blood flow rates (i. ...


References

  • H. Anger. A new instrument for mapping gamma-ray emitters. Biology and Medicine Quarterly Report UCRL, 1957, 3653: 38. (University of California Radiation Laboratory, Berkeley)
  • Anger HO. Scintillation camera with multichannel collimators. J Nucl Med 1964 Jul;65:515-31. PMID 14216630
  • PF Sharp, et al, Practical Nuclear Medicine, IRL Press, oxford
  • D. Gagnon, C.G. Matthews, US Patent #6,359,279 & #6,552,349

  Results from FactBites:
 
Spotlight: Gamma Camera (460 words)
Gamma imagers have been used in hospitals for several years, allowing radiographers to observe in detail a patient's lymph nodes and reveal tumours.
Lees' camera could be used in parallel with the bigger gamma cameras to zoom in more closely on a tumour or diseased joints.
An additional detector layer on the CCD is sensitive to the gamma radiation emitted by the radioisotope.
Gamma ray - Wikipedia, the free encyclopedia (1872 words)
Gamma rays (often denoted by the Greek letter gamma, γ) are an energetic form of electromagnetic radiation produced by radioactive decay or other nuclear or subatomic processes such as electron-positron annihilation.
Gamma rays are a form of ionizing radiation; they are more penetrating than either alpha or beta radiation (neither of which is electromagnetic radiation), but less ionizing.
Gamma rays, x-rays, visible light, and UV rays are all forms of electromagnetic radiation.
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