The detective quantum efficiency of medical x-ray image intensifiers

The recognition of small features of low contrast in the image recorded by an x-ray image intensifier is usually limited by photon noise. This detail-contrast perceptibility is dependent on the detective quantum efficiency (DQE) and the modulation transfer function of the imaging tube and associated scanning system. The DQE can be calculated for all input photon energies from the statistical behavior of each stage of photon detection and amplification where quanta are lost or converted. The potential improvement to be obtained from any proposed design change can be estimated. The escape of characteristic photons from the input phosphor layer causes significant change to the performance particularly when gadolinium oxysulphide is employed for that purpose.