Performance evaluation of a Se/CMOS prototype x-ray detector with the Apodized Aperture Pixel (AAP) design

An x-ray detector’s ability to produce high signal-to-noise ratio (SNR) images for a given exposure is described by the detective quantum efficiency (DQE) as a function of spatial frequency. Current mammography and radiography detectors have poor DQE performance at high frequencies due to noise aliasing when using a high- resolution converter layer. The Apodized-Aperture Pixel (AAP) design is novel detector design that increases high-frequency DQE by removing noise aliasing using smaller sensor elements (eg. 5 - 50 μm) than image pixel size (eg. 50 - 200 μm). The purpose of this work is to implement the AAP design on a selenium (Se) CMOS micro-sensor prototype with 7.8 × 7.8 μm size elements. Conventional (binned) and AAP images with 47 μm pixel size were synthesized and used to measure the modulation transfer function (MTF), normalized Wiener noise power spectrum (NNPS) and DQE. A micro-focus x-ray source (with a tungsten target) and a 60kV beam filtered with 2mm of aluminum was used to measure performance with DQEPro (DQEInstruments Inc., London, Canada) in a dynamic image acquisition mode at a high exposure level (9.7mR). The AAP design has 1.5x greater MTF near the image cut-off frequency (uc = 10.6 cyc/mm) than conventional design. DQE near ucwas 2.5x greater with the AAP design than conventional, and specimen imaging of a kidney stone shows greater SNR of fine-detail in the AAP image.