The quantum efficiency of a detector is a primary metric of performance because it describes the fraction of incident quanta that interact and therefore affected image quality.
This is critically important in x-ray medical imaging as it tells us that radiation exposures to patients can only be kept as low as possible if the DQE is made as close to unity as possible.
The DQE is generally expressed in terms of Fourier-based spatial frequencies as:[10] where u is the spatial frequency variable in cycles per millimeter, q is the density of incident x-ray quanta in quanta per square millimeter, G is the system gain relating q to the output signal for a linear and offset-corrected detector, T(u) is the system modulation transfer function, and W(u) is the image Wiener noise power spectrum corresponding to q.
A report by the International Electrotechnical Commission (IEC 62220-1)[12] was developed in an effort to standardize methods and algorithms required to measure the DQE of digital x-ray imaging systems.
It's the combination of very low noise and superior contrast performance that allows some digital x-ray systems to offer such significant improvements in the detectability of low-contrast objects - a quality that is best quantified by a single parameter, the DQE.
Equally important, high DQE provides the requisite foundation for advanced digital applications - dual-energy imaging, tomosynthesis, and low-dose fluoro, for instance.
Combined with advanced image-processing algorithms and fast acquisition and readout capability, high DQE is key to making such applications as these clinically practical in the years to come.