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Characterization of a Silicon Strip Photon-Counting Detector in the Presence of Compton Scatter: A Simulation Study

B Ziemer

B Ziemer*, H Ding , H Cho , S Molloi , University of California, Irvine, CA


SU-F-18C-5 Sunday 4:00PM - 6:00PM Room: 18C

Purpose: To investigate the effect of Compton scatter on detection efficiency and charge-sharing for a Si strip photon-counting detector as a function of pixel pitch, slice thickness and total pixel length.

Methods: A CT imaging system employing a silicon photon-counting detector was implemented using the GATE Monte Carlo package. A focal spot size of 300 μm, magnification of 1.33, and pixel pitches of 0.1 and 0.5mm were initially investigated. A 60 kVp spectrum with 3 mm Al filter was used and energy spectral degradation based on a prototype detector was simulated. To study charge-sharing, a single pixel was illuminated, and the detector response in neighboring pixels was investigated. A longitudinally semi-infinite detector was simulated to optimize the quantum detection efficiency of the imaging system as a function of pixel pitch, slice thickness and depth of interaction. A 2.5 mm thick tungsten plate with a 0.01 mm by 1.5 mm slit was implemented to calculate the modulation transfer function (MTF) from projection-based images. A threshold of 15 keV was implemented in the detector simulation. The preliminary charge sharing investigation results considered only scattering effects and the detector electronics related factors were neglected.

Results: Using a 15 keV threshold, 1% of the pixel charge migrated into neighboring pixels with a pixel size of 0.1x0.1 mm². The quantum detection efficiency was 77%, 84%, 87% and 89% for 15 mm, 22.5 mm, 30 mm, and 45 mm length silicon detector pixels, respectively. For a pixel pitch of 0.1 mm, the spatial frequency at 10% of the maximum MTF was found to be 5.2 lp/mm. This agreed with an experimental MTF measurement of 5.3 lp/mm with a similar detector configuration.

Conclusion: Using optimized design parameters, Si strip photon-counting detectors can offer high detection efficiency and spatial resolution even in the presence of Compton scatter.

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