Abstract
In radiographic imaging, the modulation transfer function (MTF), the noise power spectrum (NPS), and the detective quantum efficiency (DQE) are usually determined and expressed as functions of spatial frequency in the detector plane. Values thus specified would be insufficient for describing the performance of the imaging system when magnification is used to offer better spatial resolution. We are presenting a computation of DQE at the object plane as descriptor. The derivation of this quantity from measurements at the detector and object planes is presented. With source-to-image receptor distance (SID) remains constant, changes in the DQE with magnification are shown to be determined primarily by the corresponding changing MTF. Measurements with a small animal X-ray imaging system of constant SID agreed with theoretical analysis.