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.
Munro
P
P
Department of Medical Biophysics, University of Toronto, Ontario, Canada.
Rawlinson
J A
JA
Fenster
A
A
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