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A Silicon-Strip Detector for Photon-Counting Spectral CT: Energy Resolution From 40 keV to 120 keV
KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.ORCID iD: 0000-0001-8560-3262
KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.ORCID iD: 0000-0002-3039-9791
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2014 (English)In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 61, no 3, 1099-1105 p.Article in journal (Refereed) Published
Abstract [en]

We are developing a segmented silicon-strip detector for spectral computed tomography. The detector operates in photon-counting mode and allows pulse-height discrimination with 8 adjustable energy bins. In this work, we determine the energy resolution of a detector module using monoenergetic x-rays from 40 keV to 120 keV, provided at the European Synchrotron Radiation Facility, Grenoble. For each incident x-ray energy, pulse height spectra at different input photon fluxes are obtained. We investigate changes of the energy resolution due to charge sharing between pixels and pulse pileup. The different incident energies are used to channel-wise calibrate the pulse-height response in terms of signal gain and offset and to probe the homogeneity of the detector module. The detector shows a linear pulse-height response in the energy range from 40 keV to 120 keV. The gain variation among the channels is below 4%, whereas the variation of the offsets is on the order of 1 keV. We find an absolute energy resolution (sigma(E)) that degrades from 1.5 keV to 1.9 keV with increasing x-ray energy from 40 keV to 100 keV. With increasing input count rate, sigma(E) degrades by approximately 4 . 10(-3) keV Mcps(-1) mm(2), which is, within error bars, the same for the different energies. The effect of charge sharing on the width of the response peak is found to be negligible.

Place, publisher, year, edition, pages
2014. Vol. 61, no 3, 1099-1105 p.
Keyword [en]
Computed tomography, energy resolution, photon-counting, silicon strip detector, spectral CT
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-148323DOI: 10.1109/TNS.2014.2300153ISI: 000337905600006Scopus ID: 2-s2.0-84903277926OAI: oai:DiVA.org:kth-148323DiVA: diva2:736549
Note

QC 20140807

Available from: 2014-08-07 Created: 2014-08-05 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Characterization and Energy Calibration of a Silicon-Strip Detector for Photon-Counting Spectral Computed Tomography
Open this publication in new window or tab >>Characterization and Energy Calibration of a Silicon-Strip Detector for Photon-Counting Spectral Computed Tomography
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Multibin photon-counting x-ray detectors are promising candidates to be applied in next generation computed tomography (CT), whereby energy information from a broad x-ray spectrum can be extracted and properly used for improving image quality and correspondingly reducing radiation dose. A silicon-strip detector has been developed for spectral CT, which operates in photon-counting mode and allows pulse-height discrimination with 8 adjustable energy bins.

Critical characteristics, energy resolution and count-rate performance, of the detector are evaluated. An absolute energy resolution (E) from 1.5 keV to 1.9 keV with increasing x-ray energy from 40 keV to 120 keV is found. Pulse pileup degrades the energy resolution by 0.4 keV when increasing the input count rate from zero to 100 Mcps mm−2, while charge sharing shows negligible effect. A near linear relationship between the input and output count rates is observed up to 90 Mcps mm−2 in a clinical CT environment. In addition, no saturation effect appears for the maximally achieved photon flux of 485 Mphotons s−1 mm−2 with a count rate loss of 30%.

The detector is energy calibrated in terms of gain and offset with the aid of monoenergetic x rays. The gain variation among channels is below 4%, whereas the variation of offsets is on the order of 1 keV. In order to do the energy calibration in a routinely available way, a method that makes use of the broad x-ray spectrum instead of using monoenergetic x rays is proposed. It is based on a regression analysis that adjusts a modelled spectrum of deposited energies to a measured pulse-height spectrum. Application of this method shows high potential to be applied in an existing CT scanner with an uncertainty of a calibrated threshold between 0.1 and 0.2 keV.

The energy-calibration method is further used in the development of a spectral response model of the detector. This model is used to accurately bin-wise predict the response of each detector channel, which is validated by two application examples. First, the model is used in combination with the inhomogeneity compensation method to eliminate ring artefacts in CT images. Second, the spectral response model is used as the basis of the maximum likelihood approach for projection-based material decomposition. The reconstructed basis images show a good separation between the calcium-like material and the contrast agents, iodine and gadolinium. Additionally, the contrast agent concentrations are reconstructed with more than 94% accuracy.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2016. 46 p.
Series
TRITA-FYS, ISSN 0280-316X ; 2016:56
National Category
Medical Equipment Engineering
Research subject
Medical Technology
Identifiers
urn:nbn:se:kth:diva-192240 (URN)978-91-7729-079-7 (ISBN)
External cooperation:
Public defence
2016-09-30, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 09:00 (English)
Opponent
Supervisors
Note

QC 20160908

Available from: 2016-09-08 Created: 2016-09-08 Last updated: 2016-09-09Bibliographically approved

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Chen, HanPersson, Mats

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