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Improving digital charge sharing compensation in photon counting detectors with a low-threshold comparator
Scott Sigao Hsieh1, Kris Iniewski2
1Department of Radiology, Mayo Clinic Rochester, Rochester, Minnesota, USA.
Medical Physics
|August 9, 2021
Summary
Adding a low-threshold comparator (LTC) to digital count summing (DCS) significantly improves charge sharing compensation in photon counting detectors (PCDs), approaching the performance of analog charge summing (ACS). This advancement enhances material decomposition image quality.
Area of Science:
- Medical Imaging Physics
- Photon Counting Detector Technology
- Image Reconstruction Algorithms
Background:
- Charge sharing in photon counting detectors (PCDs) is a key non-ideality that increases variance in material decomposition images.
- Analog charge summing (ACS) effectively compensates for charge sharing but is complex and can limit count rates.
- Digital count summing (DCS) offers a simpler alternative but has historically shown reduced effectiveness compared to ACS.
Purpose of the Study:
- To investigate the effectiveness of incorporating a low-threshold comparator (LTC) into digital count summing (DCS) for charge sharing compensation (CSC) in PCDs.
- To compare the performance of DCS with LTC against traditional ACS and DCS without LTC in simulations.
- To evaluate the impact of electronic noise on different CSC schemes.
Main Methods:
- Simulated a PCD with 4 or 8 energy bins, modeling Poisson photon arrivals and Monte Carlo charge allocation.
- Applied Gaussian electronic noise (2 keV std dev) and processed signals using four CSC schemes: no CSC, ACS, DCS, and DCS with LTC.
- Estimated water and iodine material thickness using a linear estimator and analyzed relative dose efficiencies and image contrast.
Main Results:
- All CSC schemes reduced variance in material decomposition.
- DCS with LTC demonstrated significantly improved relative dose efficiency (e.g., 3.2 in 4-bin PCD) compared to DCS without LTC (3.2 vs 2.4).
- DCS with LTC approached the performance of ACS (4.3 vs 4.8 in 4-bin PCD) and showed less sensitivity to electronic noise.
Conclusions:
- The addition of an LTC to DCS can substantially narrow the performance gap between digital and analog charge sharing compensation methods.
- This simulation-based study suggests DCS with LTC is a promising approach for improving material decomposition in PCDs.
- Experimental validation is required to confirm these simulation findings.
