| 1. |
- Dickmann, Jannis, et al.
(författare)
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A Count Rate-Dependent Method for Spectral Distortion Correction in Photon Counting CT
- 2018
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Ingår i: Medical Imaging 2018. - : SPIE - International Society for Optical Engineering. - 9781510616363
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Konferensbidrag (refereegranskat)abstract
- Rawdata-based material decomposition in spectral CT using photon-counting energy-selective detectors relies on a precise forward model that predicts a count-rate given intersection lengths for each material. This requires extensive system-specific measurements or calibration techniques. Existing calibrations either estimate a detected spectrum and are able to account for spectrally distorted assumptions or correct the predicted count rate using a correction function and can accommodate for count rate-dependent effects such as pulse pileup. We propose a calibration method that uses transmission measurements to optimize a correction function that, unlike existing methods, depends both on the photon energy and the count rate. It is thus able to correct for both kinds of distortions. In a simulated material decomposition into water and iodine, the error was reduced by 96% compared to the best performing reference method if only pulse pileup was present and reduced by 23% if additionally spectral distortions were taken into account. In phantom measurements using a Dectris SANTIS prototype detector, the proposed method allowed to reduce the error by 29% compared to the best performing reference method. Artifacts were below the noise level for the proposed method, while the reference methods either showed an offset in the water region or ring artifacts.
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| 2. |
- Grönberg, Fredrik, et al.
(författare)
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Count statistics and pileup correction for nonparalyzable photon counting detectors with finite pulse length
- 2018
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Ingår i: Medical Imaging 2018. - : SPIE - International Society for Optical Engineering. - 9781510616363
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Konferensbidrag (refereegranskat)abstract
- Photon counting detectors are expected to be the next big step in the development of medical computed tomography. Accurate modeling of the behavior of photon counting detectors in the high count rate regime is therefore important for detector performance evaluations and the development of accurate image reconstruction methods. The commonly used ideal nonparalyzable detector model is based on the assumption that photon interactions are converted to pulses with zero extent in time, which is too simplistic to accurately predict the behavior of photon counting detectors in both low and high count rate regimes. In this work we develop a statistical count model for a nonparalyzable detector with finite pulse length and use it to derive the asymptotic mean and variance of the output count distribution using tools from renewal theory. We use the statistical moments of the distribution to construct an estimator of the true number of counts for pileup correction. We con firm the accuracy of the model and evaluate the pileup correction using Monte Carlo simulations. The results show that image quality is preserved for surprisingly high count rates.
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| 3. |
- Sundberg, Christel, et al.
(författare)
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Increasing the dose efficiency in silicon photon-counting detectors utilizing dual shapers
- 2018
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Ingår i: Medical Imaging 2018. - : SPIE - International Society for Optical Engineering. - 9781510616363
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Konferensbidrag (refereegranskat)abstract
- Silicon photon-counting spectral detectors are candidates for the next generation of medical CT. For silicon detectors, a low noise floor is necessary to obtain good detection efficiency. A low noise floor can be obtained by having a slow shaping filter in the ASIC, but this leads to a long dead-time, thus decreasing the count-rate performance. In this work, we evaluate the benefit of utilizing two sub-channels with different shaping times. It is shown by simulation that utilizing a dual shaper can increase the dose efficiency for equal count-rate capability by up to 17%.
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