Program Information
Exploring the Maximum Count Rate Capabilities of Photon Counting Arrays Based On Polycrystalline Silicon
A K Liang*, M Koniczek , L E Antonuk , Y El-Mohri , Q Zhao , University of Michigan, Ann Arbor, MI
Presentations
TU-FG-209-3 (Tuesday, August 2, 2016) 1:45 PM - 3:45 PM Room: 209
Purpose
Photon counting arrays (PCAs) offer several advantages over conventional, fluence-integrating x-ray imagers, such as improved contrast by means of energy windowing. For that reason, we are exploring the feasibility and performance of PCA pixel circuitry based on polycrystalline silicon. This material, unlike the crystalline silicon commonly used in photon counting detectors, lends itself toward the economic manufacture of radiation tolerant, monolithic large area (e.g., ~43x43 cm2) devices. In this presentation, exploration of maximum count rate, a critical performance parameter for such devices, is reported.
Methods
Count rate performance for a variety of pixel circuit designs was explored through detailed circuit simulations over a wide range of parameters (including pixel pitch and operating conditions) with the additional goal of preserving good energy resolution. The count rate simulations assume input events corresponding to a 72 kVp x-ray spectrum with 20 mm Al filtration interacting with a CZT detector at various input flux rates. Output count rates are determined at various photon energy threshold levels, and the percentage of counts lost (e.g., due to deadtime or pile-up) is calculated from the ratio of output to input counts. The energy resolution simulations involve thermal and flicker noise originating from each circuit element in a design.
Results
Circuit designs compatible with pixel pitches ranging from 250 to 1000 μm that allow count rates over a megacount per second per pixel appear feasible. Such rates are expected to be suitable for radiographic and fluoroscopic imaging. Results for the analog front-end circuitry of the pixels show that acceptable energy resolution can also be achieved.
Conclusions
PCAs created using polycrystalline silicon have the potential to offer monolithic large-area detectors with count rate performance comparable to those of crystalline silicon detectors. Further improvement through detailed circuit simulations and prototyping is expected. Partially supported by NIH grant R01-EB000558.
Funding Support, Disclosures, and Conflict of Interest: This work was partially supported by NIH grant no. R01-EB000558.
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