Screen Film Radiology
Screen Film Radiology
Screen Film Radiology
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4. Absorption Efficiency (AE)<br />
v The absorption efficiency or<br />
QDE describes how efficiently<br />
the screen detects x-ray photons<br />
that are incident upon it<br />
v X-ray photon absorbed by the<br />
screen deposits its energy and<br />
some fraction of energy is<br />
converted to light photons<br />
v <strong>Screen</strong>-film systems are energy<br />
detectors<br />
The number of light photons<br />
produced in the screen is<br />
determined by the total<br />
amount of x-ray energy<br />
absorbed by the screen, not<br />
by the number of x-ray<br />
photons<br />
c.f. Bushberg, et al. The Essential Physics of<br />
Medical Imaging, 2 nd ed., pp. 154-155.<br />
4. Overall Efficiency of a <strong>Screen</strong>-<strong>Film</strong> System<br />
v Total efficiency = AE · CE<br />
v A SF system increases x-ray<br />
detection efficiency compared to<br />
film only (29.5% vs. 0.65% at 80<br />
kVp)<br />
v Using film-screen versus film only<br />
reduces radiation dose to patient by<br />
a factor of 50!<br />
v Intensification factor (IF) = ratio of<br />
energy absorption of 120 mg/cm 2<br />
phosphor vs. 0.80 mg/cm 2 AgBr<br />
v An IF of 50 is achieved for Gd2O2S over the x-ray<br />
energy spectra commonly used for diagnostic<br />
examination<br />
c.f. Bushberg, et al. The Essential Physics of<br />
Medical Imaging, 2 nd ed., p. 156.<br />
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