SU‐F‐18C‐05: Characterization of a Silicon Strip Photon‐Counting Detector in the Presence of Compton Scatter: A Simulation Study

• Published in: Medical physics (Lancaster) Vol. 41; no. 6Part23; pp. 403 - 404
• Main Authors: Ziemer, B, Ding, H, Cho, H
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01-06-2014
• Subjects: 60 APPLIED LIFE SCIENCES; Charge transfer; Compton scattering; Computed tomography; COMPUTERIZED SIMULATION; EFFICIENCY; Image detection systems; Image sensors; INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND TECHNOLOGY; Medical imaging; Modulation transfer functions; MONTE CARLO METHOD; Photon scattering; SI SEMICONDUCTOR DETECTORS; Silicon; Silicon detectors; SPATIAL RESOLUTION; THICKNESS
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4889089

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 semiinfinite 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 0.1×0.1 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.