Therapy imaging: a signal-to-noise analysis of metal plate/film detectors.
We have measured the modulation transfer functions [MTF (f)'s] and the noise power spectra [NPS (f)] of therapy x-ray detectors irradiated by 60Co, 6- and 18-MV radiotherapy beams. Using these quantities, we have calculated the noise-equivalent quanta [NEQ (f)] and the detective quantum efficiency [DQE (f)] to quantitate the limitations of therapy detectors. The detectors consisted of film or fluorescent screen-film combinations in contact with copper, lead, or tungsten metal plates. The resolution of the detectors was found to be comparable to fluorescent screen-film combinations used in diagnostic radiology, however, the signal-to-noise ratio [SNR (f)] of the detectors was limited due to film granularity. We conclude that improved images can be obtained by using alternative detector systems which have less noise or film granularity.
Department of Medical Biophysics, University of Toronto, Ontario, Canada.
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P
Munro
J A
JA
Rawlinson
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A
Fenster
D003037:Cobalt Radioisotopes / Q000627:therapeutic use; D006801:Humans; D011789:Quantum Theory; D011859:Radiography / Q000295:instrumentation*; D011878:Radiotherapy / Q000379:methods*; D014965:X-Rays
D003037:Cobalt Radioisotopes