Practical method for detected quantum efficiency (DQE) assessment of digital mammography systems in the radiological environment

Abstract

X-ray detector systems can be characterized by their measured or estimated detective quantum efficiency (DQE). Assessment of DQE includes a measurement of the modulation transfer function (MTF) and the normalized noise power spectrum (NNPS). The incoming X-ray quantum flux has to be estimated. In this paper, the influence of the different possibilities regarding the measurement methods and phantoms, the X-ray quantum flux estimation models and the exposure geometry on the DQE of a full field digital mammography detector is assessed. Physical models were used to fit MTF measurements from bar-pattern and edge phantoms. The NNPS was calculated by 2D-FFT on a large number of flat-field subimages. The flux was calculated using anode spectra models (Boone, 1997) and attenuation data (NIST). We compared the influence of scattered radiation MTF calculations of both phantoms were similar. The edge method is preferred for practical reasons. NNPS data were similar to 1D synthetic-slit measurements. DQE data compared well with literature. Different exposure geometry conditions (with scattered radiation) showed similar results but a siginificantly lower DQE than in absence of scattered radiation. DQE assessment is feasible using normal exposure conditions, an edge phantom and calculated estimations of the flux.