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Evaluation of Energy Loss and Charge Sharing in Cadmium Telluride Detectors for Photon-Counting Computed Tomography
KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.ORCID iD: 0000-0002-3039-9791
KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
2011 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 58, no 3, 614-625 p.Article in journal (Refereed) Published
Abstract [en]

We present estimates of energy loss and charge sharing for a pixelated cadmium telluride (CdTe) detector used for photon-counting spectral computed tomography (CT). In a photon-counting pixelated CdTe detector, several physical effects lead to detected events with reduced energies, including Compton scattering, fluorescence emission, charge diffusion, trapping of charge carriers and slow-hole-motion-induced incomplete charge collection. Charge sharing is the result of the lost energy being collected by adjacent pixels. We simulated the photon transport and the charge-collection process with a Monte Carlo-based simulation and evaluated these effects on the detector performance. The trapping effect and poor hole collection have been studied together using an analytical model. We also investigated the detector response under the influence of only the fluorescence effect. We conclude that the charge sharing effects should be taken into account when the pixel is smaller than 1 mm(2). A straightforward way to decrease the double counting of X-rays from events with charge sharing is to increase the electronic threshold. However, increasing the threshold comes at the cost of losing low-energy events, which is undesirable, at least in applications such as pediatric imaging.

Place, publisher, year, edition, pages
2011. Vol. 58, no 3, 614-625 p.
Keyword [en]
Cadmium telluride, charge sharing, computed tomography, energy loss, Monte Carlo simulation, photon counting, signal generation
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-35618DOI: 10.1109/TNS.2011.2122267ISI: 000291655900005Scopus ID: 2-s2.0-79959378612OAI: oai:DiVA.org:kth-35618DiVA: diva2:429612
Note
QC 20110705Available from: 2011-07-05 Created: 2011-07-04 Last updated: 2017-12-11Bibliographically 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)
Opponent
Supervisors
Note

QC 20121123

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

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