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Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

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FIGURE 24-1. <strong>The</strong> geometry <strong>for</strong>measuring the output free-in-air of aradiographic system is shown.• In<strong>for</strong>mation regarding the characteristics (HVL or inherent filtration) of thebeam produced by the x-ray machine• An estimate of the patient's thickness <strong>for</strong> each radiographic projectionFigure 24-1 illustrates the measurement geometry that is used to measure theoutput characteristics of an x-ray tube. <strong>The</strong> parameter mGy (air kerma) per mAs (ortraditional units of mR per mAs), measured at 100 cm from the focal spot, shouldbe obtained <strong>for</strong> every x-ray tube in an institution, and typical values are shown inFig. 24-2. Armed with the data in Fig. 24-2 (air kerma per mAs at 100 cm), the25 218.3X-ray tube output @ 100 em20 174.6'"'"~ 15 131.0 ~•...•...0) 0)0., 0.,~ 10 87.3 6'~5 43.780 100kVpFIGURE 24-2. <strong>The</strong> output (in mRper mAs and mGy per mAs) <strong>for</strong> atypical x-ray system measured at asource-to-detector distance of 100em.

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