The detective quantum efficiency of cadmium telluride photon‐counting x‐ray detectors in breast imaging applications

Abstract

Purpose In breast imaging applications, cadmium telluride (CdTe) photon counting x‐ray detectors (PCDs) may reduce radiation dose and enable single‐shot multi‐energy x‐ray imaging. The purpose of this work is to determine the upper limits of the detective quantum efficiency (DQE) of CdTe PCDs for x‐ray mammography and to compare them with the published DQEs of energy‐integrating detectors (EIDs) and other PCDs. Methods We calibrated and validated a Monte Carlo (MC) model of the DQE of CdTe PCDs using an XCounter CdTe PCD. Our model accounted for charge sharing, electronic noise, and charge summation logic. We used a 28 kVp Mo/Mo spectrum hardened by 3.9 cm of Lucite to optimize the detector thickness and energy threshold for pixel sizes of 50, 85, and 100 μ${{\mu}}$m with and without inter‐pixel charge summation logic. The figure of merit used for optimization was the integral of the DQE, which is equivalent to the detectability index for a delta function task function, which represents a high‐frequency task. Results For an electronic noise level equal to that of the XCounter, the optimal DQE(0) without charge summing was 0.74. Charge summing for charge‐sharing correction reduced DQE(0) by 14% due to an increase in electronic noise. Reducing the electronic noise to ∼0.5 keV per pixel in combination with charge summing resulted in DQE(0) ≈$ \approx $0.78 for 85 μ${{\mu}}$m pixels, which is approximately equal to that of a‐Se and slot‐scanning silicon‐strip PCDs. At higher spatial frequencies, and for matched pixel sizes, the DQE was inferior to that of a‐Se EIDs and superior to that of slot‐scanning silicon‐strip PCDs in the scan direction but inferior in the slit direction. Conclusions (1) CdTe PCDs have the potential to provide a zero‐frequency DQE equal to that of a‐Se EIDs and slot‐scanning silicon‐strip PCDs, but this will require electronic noise levels ∼0.5 keV per pixel. (2) At mid‐to‐high spatial frequencies the DQE of CdTe PCDs may be (a) inferior to that of a‐Se EIDs and slot‐scanning silicon‐strip PCDs in the slit direction, and (b) superior to slot‐scanning silicon‐strip PCDs in the scan direction.

An experimentally validated simulation model of a two-bin flat-panel cadmium telluride photon-counting detector for spectroscopic breast imaging applications

“…The simulation model presented is an extension of the model presented in our previous work. 6 Similarly this model was based on an XCounter Thor CdTe PCD with a 750um thick active layer and 100um pixel pitch with charge summation enabled.…”

“…Unlike our previous work 6 the input energy spectrum is not generated using the Tucker and Barnes algorithm 10 until image quality metrics were calculated. Similar to the approach by Persson et al 11 , the input energy spectrum is a series of mono-energetic sources from 10 keV to 50 keV in 0.5-keV increments.…”

“…4 Both cadmium telluride (CdTe) and silicon PCDs show promising benefits for mammography providing image resolutions equal to amorphous selenium energy integrating detectors in standard screening mammography. 6,7 While silicon slot scanning detectors remain the only clinically used PCDs for mammography, flat panel CdTe PCDs remain competitive in screening mammography and show more consistent image resolution inboth imaging directions; comparable to the redial resolution of slot scan silicon PCDs. 6 The performace capabilities of CdTe PCDs for standard mammography warrant a detailed investigation into their imaging potential for contrast enhanced spectral mammography.…”

“…6,7 While silicon slot scanning detectors remain the only clinically used PCDs for mammography, flat panel CdTe PCDs remain competitive in screening mammography and show more consistent image resolution inboth imaging directions; comparable to the redial resolution of slot scan silicon PCDs. 6 The performace capabilities of CdTe PCDs for standard mammography warrant a detailed investigation into their imaging potential for contrast enhanced spectral mammography. Due to high fabrication costs, the development an optimized CdTe PCD is best performed using a model based on a prototype detector.…”

Monte‐Carlo study of contrast‐enhanced spectral mammography with cadmium telluride photon‐counting x‐ray detectors

“…In addition, we recently showed that the spatial resolution of CdTe PCDs is expected to be superior to that of slot-scanning silicon PCDs. 11 Ghammraoui et al 12 investigated CdTe detectors for breast density mea-surements, and Ding et al 13 investigated cadmium zinc telluride for measurement of the water, lipid, and protein content in breasts, but there has been little work on CdTe for CESM.…”