TY - BOOK
T1 - Spectral Correction and Application of Single-Photon Imaging with Direct Conversion X-ray Detectors
AU - Dreier, Erik Schou
PY - 2019
Y1 - 2019
N2 - Direct conversion X-ray detectors with single-photon sensitivity have the potential to improve X-ray imaging techniques ranging from diraction measurements to high- ux X-ray scanners. These detectors' ability to perform energy resolved X-ray imaging is actively researched and is likely to enhance the capabilities of material identication techniques. However, charge collection artifacts, such as charge sharing and photon pileup, may deteriorate the quality of the measured spectrum and aect small pixel pitched detectors' spatial resolution. In this thesis, I show how more accurate X-ray spectra can be retrieved by mitigating the distorting eect of charge collection artifacts. The spectral distortion was mitigated using a comprehensive computational algorithm. The algorithm was made for the CdTe detector Multix ME100, and it uses a Monte Carlo simulation of the detector response together withiterative models to correct the spectrum for a range of artifacts. The algorithm is fast enough for real-time correction and suciently reliable for material discrimination research. Using fast readout electronics, charge sharing is not just something to be mitigated but can be actively used for single-photon subpixel localization through measuring the spatial distribution of the charge each photon excites in the detector sensor. I demonstrate in this thesis how the fast Timepix3 readout chip with 55 m pixel pitch can obtain single-photon position precision of < 19:3 m in a CdTe sensor using charge sharing. Furthermore, the high resolution oered by single-photon subpixel localization can be used to perform single-shot laboratory-based multimodal X-ray imaging. Multimodal imaging here refers to the simultaneous measurement of X-ray attenuation, dierential phase (refraction), and dark-eld (scattering) contrast. Dierential phase contrast is used to increase the sensitivity for low absorbing materials and the dark-eld contrast enables the detection of sub-resolution sample features. In this thesis, I exploit single-photon localization to present the rst two multimodal imaging setups with single-shot, directional dark-eld sensitivity using the beam-tracking technique. The setups use two dierent silicon-based direct conversion detectors: The photon counting Advapix detector with the Timepix3 readout chip and the analog readout MONCH detector. The Advapix setup uses a 200 m thick tungsten mask with a square array of conically shaped apertures to obtain multimodal images. The results indicate that single-photon subpixel resolution can signicantly improve the precision of dierential phase contrast images acquired with a beam-tracking setup. Furthermore, the Advapix setup is shown to reduce the exposure needed for omni-directional dark-eld imaging with up to a factor of 30, compared to competing single-shot multimodal techniques. The MONCH detector setup is demonstrated to obtain qualitatively correct omni-directional multimodal images at a single-shot resolution of just 19:5 m. For both setups, I use the direct conversion detectors' energy sensitivity to remove high-energy X-rays in order to increase the dark-eld contrast.
AB - Direct conversion X-ray detectors with single-photon sensitivity have the potential to improve X-ray imaging techniques ranging from diraction measurements to high- ux X-ray scanners. These detectors' ability to perform energy resolved X-ray imaging is actively researched and is likely to enhance the capabilities of material identication techniques. However, charge collection artifacts, such as charge sharing and photon pileup, may deteriorate the quality of the measured spectrum and aect small pixel pitched detectors' spatial resolution. In this thesis, I show how more accurate X-ray spectra can be retrieved by mitigating the distorting eect of charge collection artifacts. The spectral distortion was mitigated using a comprehensive computational algorithm. The algorithm was made for the CdTe detector Multix ME100, and it uses a Monte Carlo simulation of the detector response together withiterative models to correct the spectrum for a range of artifacts. The algorithm is fast enough for real-time correction and suciently reliable for material discrimination research. Using fast readout electronics, charge sharing is not just something to be mitigated but can be actively used for single-photon subpixel localization through measuring the spatial distribution of the charge each photon excites in the detector sensor. I demonstrate in this thesis how the fast Timepix3 readout chip with 55 m pixel pitch can obtain single-photon position precision of < 19:3 m in a CdTe sensor using charge sharing. Furthermore, the high resolution oered by single-photon subpixel localization can be used to perform single-shot laboratory-based multimodal X-ray imaging. Multimodal imaging here refers to the simultaneous measurement of X-ray attenuation, dierential phase (refraction), and dark-eld (scattering) contrast. Dierential phase contrast is used to increase the sensitivity for low absorbing materials and the dark-eld contrast enables the detection of sub-resolution sample features. In this thesis, I exploit single-photon localization to present the rst two multimodal imaging setups with single-shot, directional dark-eld sensitivity using the beam-tracking technique. The setups use two dierent silicon-based direct conversion detectors: The photon counting Advapix detector with the Timepix3 readout chip and the analog readout MONCH detector. The Advapix setup uses a 200 m thick tungsten mask with a square array of conically shaped apertures to obtain multimodal images. The results indicate that single-photon subpixel resolution can signicantly improve the precision of dierential phase contrast images acquired with a beam-tracking setup. Furthermore, the Advapix setup is shown to reduce the exposure needed for omni-directional dark-eld imaging with up to a factor of 30, compared to competing single-shot multimodal techniques. The MONCH detector setup is demonstrated to obtain qualitatively correct omni-directional multimodal images at a single-shot resolution of just 19:5 m. For both setups, I use the direct conversion detectors' energy sensitivity to remove high-energy X-rays in order to increase the dark-eld contrast.
UR - https://soeg.kb.dk/permalink/45KBDK_KGL/1ed7rpq/alma99123213868205763
M3 - Ph.D. thesis
BT - Spectral Correction and Application of Single-Photon Imaging with Direct Conversion X-ray Detectors
PB - Niels Bohr Institute, Faculty of Science, University of Copenhagen
ER -