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Validity of spherical approximations of initial charge cloud shape in silicon detectors
KTH, School of Engineering Sciences (SCI), Physics. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova. (Medicinsk bildfysik)
KTH, School of Engineering Sciences (SCI), Physics. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova. (Medicinsk bildfysik)ORCID iD: 0000-0002-3039-9791
KTH, School of Engineering Sciences (SCI), Physics. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova. (Medicinsk bildfysik)
2011 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 648, no SUPPL. 1, 190-193 p.Article in journal (Refereed) Published
Abstract [en]

Spherical approximation has been used extensively in low-energy X-ray imaging to represent the initial charge cloud produced by photon interactions in silicon detectors, mainly because of its simplicity. However, for high-energy X-rays, where the initial charge distribution is as important as the diffusion process, the spherical approximation will not result in a realistic detector response. In this paper, we present a bubble-line model that simulates the initial charge cloud in silicon detectors for photons in the energy range of medical imaging. An initial charge cloud can be generated by sampling the center of gravity and the track size from statistical distributions derived from Monte Carlo generated tracks and by distributing a certain proportion of photon energy into a bubble (68%) and a line portion uniformly. The simulations of detector response demonstrate that the new model simulates the detector response accurately and corresponds well to Monte Carlo simulation.

Place, publisher, year, edition, pages
2011. Vol. 648, no SUPPL. 1, 190-193 p.
Keyword [en]
Spherical approximation; Statistical model; Monte Carlo simulation; Signal induction; Silicon
National Category
Other Physics Topics
Identifiers
URN: urn:nbn:se:kth:diva-47662DOI: 10.1016/j.nima.2010.11.173ISI: 000305376900049Scopus ID: 2-s2.0-79960835983OAI: oai:DiVA.org:kth-47662DiVA: diva2:455935
Note
QC 20111115Available from: 2011-11-11 Created: 2011-11-11 Last updated: 2017-12-08Bibliographically approved
In thesis
1. A Segmented Silicon Strip Detector for Photon-Counting Spectral Computed Tomography
Open this publication in new window or tab >>A Segmented Silicon Strip Detector for Photon-Counting Spectral Computed Tomography
2012 (English)Doctoral thesis, comprehensive summary (Other academic) [Artistic work]
Abstract [en]

Spectral computed tomography with energy-resolving detectors has a potential to improve the detectability of images and correspondingly reduce the radiation dose to patients by extracting and properly using the energy information in the broad x-ray spectrum. A silicon photon-counting detector has been developed for spectral CT and it has successfully solved the problem of high photon flux in clinical CT applications by adopting the segmented detector structure and operating the detector in edge-on geometry. The detector was evaluated by both the simulation and measurements.

The effects of energy loss and charge sharing on the energy response of this segmented silicon strip detector with different pixel sizes were investigated by Monte Carlo simulation and a comparison to pixelated CdTe detectors is presented. The validity of spherical approximations of initial charge cloud shape in silicon detectors was evaluated and a more accurate statistical model has been proposed.

A photon-counting energy-resolving application specific integrated circuit (ASIC) developed for spectral CT was characterized extensively by electrical pulses, pulsed laser and real x-ray photons from both the synchrotron and an x-ray tube. It has been demonstrated that the ASIC performs as designed. A noise level of 1.09 keV RMS has been measured and a threshold dispersion of 0.89 keV RMS has been determined. The count rate performance of the ASIC in terms of count loss and energy resolution was evaluated by real x-rays and promising results have been obtained.

The segmented silicon strip detector was evaluated using synchrotron radiation. An energy resolution of 16.1% has been determined with 22 keV photons in the lowest flux limit, which deteriorates to 21.5% at an input count rate of 100 Mcps mm−2. The fraction of charge shared events has been estimated and found to be 11.1% for 22 keV and 15.3% for 30 keV. A lower fraction of charge shared events and an improved energy resolution can be expected by applying a higher bias voltage to the detector.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. viii, 43 p.
Series
Trita-FYS, ISSN 0280-316X ; 2012:88
Keyword
photon counting, spectral computed tomography, silicon strip detector, ASIC, energy resolution, cadmium telluride, charge sharing, Monte Carlo simulation, synchrotron
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Medical Equipment Engineering Medical Laboratory and Measurements Technologies Other Engineering and Technologies not elsewhere specified Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:kth:diva-105614 (URN)978-91-7501-589-7 (ISBN)
Public defence
2012-12-14, FA32, AlbaNova University Center, KTH, Roslagstullsbacken 21, Stockholm, 13:15 (English)
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Note

QC 20121123

Available from: 2012-11-23 Created: 2012-11-23 Last updated: 2012-11-23Bibliographically approved

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