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AIIMS AIIMS Solved Paper-2003

  • question_answer
    In a material medium, when a positron meets an electron both the particles annihilate leading to the emission of two gamma ray photons. This process forms the basis of an important diagnostic procedure called:

    A)  MRI    

    B)                                        PET                       

    C)        CAT                      

    D)        SPECT

    Correct Answer: B

    Solution :

    Positron emission tomography (PET) is a nuclear medicine medical imaging technique which produces a three dimensional image or map of functional process m the body. A short lived radioactive tracer isotope which decays by emitting a positron chemically incorporated into a metabolically active molecule, is injected into the living subject (usually into blood circulation). There is a waiting period after which the short-lived isotope decays, emitting a positron. After travelling up to a few millimetres the positron annihilates with an electron, producing a pair of annihilation photons (similar to gamma rays) moving in opposite directions.


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