Feasibility study of CMOS detectors for mammography

We investigated the potential use of CMOS (complementary metal-oxide-semiconductor) imaging detectors with a pixel pitch of 48 μm for mammography. Fundamental imaging characteristics were evaluated in terms of modulation-transfer function (MTF), noise-power spectrum (NPS), and detective quantum efficiency (DQE). The magnitudes of various image noise sources, such as optical photons, direct x rays unattenuated and scattered x rays from the scintillator, and additive electronic noise, were measured and analyzed. For the analysis of the measurement results, we applied a model describing the signal and noise transfer based on the cascaded linear-systems approach. The direct x-ray was very harmful to the detector noise performance with white noise characteristics in the spatial frequency domain, and which significantly degraded the spatial-frequency-dependent DQE at higher frequencies. Although the use of a fiber-optic plate (FOP) reduces the detector sensitivity and the MTF performance, it enhances the DQE performance by preventing the direct x-ray photons from the absorption within the photodiode array.

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