Dr. Denny Lee Profile

Dr. Denny Lee

at Univ of Waterloo

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Publications (2)

Proceedings Article | 16 March 2020 Paper

Performance of amorphous selenium-based unipolar charge sensing detector for photon counting x-ray imaging

Ahmet Camlica, Denny Lee, Hyunsuk Jang, Salman Arnab, Yuan Fang, M. Kabir, Karim Karim

Proceedings Volume 11312, 113120G (2020) https://doi.org/10.1117/12.2550318

KEYWORDS: Sensors, Electrodes, Signal detection, Photon counting, Selenium, Photoresistors, Electric field sensors, Near field, X-ray imaging, Photodetectors

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Proceedings Article | 12 March 2018 Paper

Increased temporal resolution of amorphous selenium detector using preferential charge sensing approach

Ahmet Camlica, Denny Lee, Karim Karim

Proceedings Volume 10573, 105735W (2018) https://doi.org/10.1117/12.2293889

KEYWORDS: Sensors, Electrodes, X-rays, Selenium, Electrons, Spatial resolution, Real time imaging, Temporal resolution, Photoresistors, X-ray detectors

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Amorphous selenium (a-Se) is a direct conversion photoconductor capable of very high spatial resolution that can enable early detection of small and subtle lesions. A-Se also offers cost effective and reliable coupling to large area readout circuitry. Currently, the highest performance commercial flat panel detectors used for mammography are based on a-Se technology. However, this inherent spatial resolution has not been leveraged for real-time imaging applications, e.g. micro- angiography for imaging fine brain vessels that requires spatial resolution approaching 20 lp/mm, which is achievable with selenium technology. The challenge is that a-Se detectors suffer from memory artifacts such as lag that limits the frame rate of the X-ray imager. The frame rate reduction is attributed primarily to lag, which manifests itself as an increased dark conductivity after an X-ray exposure. Increased lag degrades the temporal response of the detector and makes a-Se photoconductor impractical for real-time imaging. Furthermore, high ionization energy required for electron-hole pair creation with a-Se limits the sensitivity of detector for a given X-ray dose, achieving a quantum noise limited system become a challenge. In this study, we investigate preferential sensing of those charge carriers having a higher mobility, i.e. holes for a-Se, to improve the temporal response of a-Se detectors for real-time imaging. A new preferential charge sensing detector with a field shaping internal grid, called Multi Pixel Proportional Counter, is fabricated and tested under the typical clinical usage conditions similar to that of fluoroscopy. The fabricated detector offers high frame rate and low noise imaging through avalanche gain. Conventional a-Se detectors are also fabricated for comparison purposes. Experimental results show that image lag as low as 1% can be achieved with the new structure with an internal grid while the conventional detector exhibits higher lag around 5%.

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