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Positron emission tomography Essay Example

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Positron emission tomography

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When the positrons arrive at thermal energies, they begin connecting with electrons either by annihilation, which produces two 511 keV photons that are anti-parallel in the positronís frame, or through development of a hydrogen-like orbiting couple known as positronium. At its foundation condition, positronium has two types’ of- ortho-positronium, where the spins of the electron and positron are parallel, and para-positronium, where the spins are anti-parallel. However, Para-positronium decomposes again through self- annihilation those end up in creation of two anti-parallel 511 keV photons. Ortho-positronium self-annihilates by the emission of three photons.The photons spread along nearly collinear paths, with the degree of noncollinearity relying on the momentum of the positron and electron when they annihilated. Parting from collinearity is around a single degree or less and is not into considerations. The extent to which the positrons move before annihilating is positron range. The significance of the scope relies on positron energy, which differs in different isotopes. However, positron scope is much smaller than the resolution of most scanners, so it is not a serious source of error and is usually no tin consideration. The limit positron scope and the non-collinearity of the annihilation photons give rise to an inherent positional in absolute not present in the conventional single photon emission techniques. However, other features of PET are in discussion below more than offset this disadvantage.The only two possibilities of interactions at 511 keV are photoelectric concentration and Compton scatter. In photoelectric absorption, an atom concentrates a photon and in the process, an electron is let out from one of its bound shells. The chance of photoelectric concentration enlarges faster with increasing atomic amount of the concentrator atom, and reduces faster with enlarging photon energy. However, in water, the probability of photoelectric absorption decreases with roughly the 3rd power of the photon energy and is negligible at 511 keV.During an ordinary connection, the photon connects with an outer shell electron such that its way is in deflection and some of its strength is lost. Most of the scattering photons encounter reduction of energy and a related transformation of direction are scattered out of

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preview essay on Positron emission tomography
  • Pages: 6 (1500 words)
  • Document Type: Essay
  • Subject: Physics
  • Level: Undergraduate
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