Dr. Willem H. Maes Profile

Dr. Willem H. Maes

at Teledyne DALSA

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Proceedings Article | 16 March 2020 Paper

Extended dynamic range CMOS active pixel architecture for x-ray detectors

Willy Maes, Olivier Tousignant, Ruud J. Vullers, Yves Kessener, James Miller, Inge Peters

Proceedings Volume 11312, 113123Z (2020) https://doi.org/10.1117/12.2549236

KEYWORDS: Sensors, X-rays, X-ray detectors, X-ray imaging, Image quality, CMOS sensors, Switches, Capacitance

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X-ray detectors increasingly utilize active pixel CMOS instead of amorphous silicon technology because of its superior noise, pixel lag, readout speed and offset stability. We already demonstrated [1] that adding an a additional pixel capacitance to a standard 3T CMOS pixel architecture allows operating the detector in either high sensitivity (HS) or high saturation dose (HD) mode. Since the charge capacity is limited in HS mode, a large signal will saturate the pixel, causing a loss of information. In HD mode, a very low exposure will lead to a loss of contrast-to-noise ratio (CNR) due to the inherently higher noise floor in this mode. Using the same 3T pixel architecture, we propose a dual readout method to combine the benefits of HS and HD modes. After a single exposure the pixel signal is read twice, respectively in HS and HD mode. The two linear signal values are then combined to create the pixel value of the final image. In this paper proof of concept is demonstrated using images acquired separately and combined offline. The benefits of this method are demonstrated for different x-ray imaging modalities such as mammography, extra-oral dental, interventional and non-destructive testing. Using different detector models, results show that extended dynamic range combined with low noise leads to better image quality without introducing artifacts. It is expected that implementing the fast CMOS-sensor dual readout and image synthesis inside the detector will preserve important application requirements such as frame rate, data bandwidth and power consumption.

Proceedings Article | 18 March 2015 Paper

Low-dose performance of wafer-scale CMOS-based X-ray detectors

Willem Maes, Inge Peters, Chiel Smit, Yves Kessener, Jan Bosiers

Proceedings Volume 9412, 94120C (2015) https://doi.org/10.1117/12.2081996

KEYWORDS: Sensors, Field emission displays, High dynamic range image sensors, X-ray detectors, CMOS sensors, X-rays, Photons, Neon, Modulation transfer functions, High dynamic range imaging

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Compared to published amorphous-silicon (TFT) based X-ray detectors, crystalline silicon CMOS-based active-pixel detectors exploit the benefits of low noise, high speed, on-chip integration and featuring offered by CMOS technology. This presentation focuses on the specific advantage of high image quality at very low dose levels. The measurement of very low dose performance parameters like Detective Quantum Efficiency (DQE) and Noise Equivalent Dose (NED) is a challenge by itself. Second-order effects like defect pixel behavior, temporal and quantization noise effects, dose measurement accuracy and limitation of the x-ray source settings will influence the measurements at very low dose conditions. Using an analytical model to predict the low dose behavior of a detector from parameters extracted from shot-noise limited dose levels is presented. These models can also provide input for a simulation environment for optimizing the performance of future detectors. In this paper, models for predicting NED and the DQE at very low dose are compared to measurements on different CMOS detectors. Their validity for different sensor and optical stack combinations as well as for different x-ray beam conditions was validated.

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