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Energy resolution of a photon-counting silicon strip detector
KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging. (Medical Imaging)
KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging. (Medical Imaging)
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2010 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, 156-162 p.Article in journal (Refereed) Published
Abstract [en]

A photon-counting silicon strip detector with two energy thresholds was investigated for spectral X-ray imaging in a mammography system. Preliminary studies already indicate clinical benefit of the detector, and the purpose of the present study is optimization with respect to energy resolution. Factors relevant for the energy response were measured, simulated, or gathered from previous studies, and used as input parameters to a cascaded detector model. Threshold scans over several X-ray spectra were used to calibrate threshold levels to energy, and to validate the model. The energy resolution of the detector assembly was assessed to range over ΔE/E=0.12–0.26 in the mammography region. Electronic noise dominated the peak broadening, followed by charge sharing between adjacent detector strips, and a channel-to-channel threshold spread. The energy resolution may be improved substantially if these effects are reduced to a minimum. Anti-coincidence logic mitigated double counting from charge sharing, but erased the energy resolution of all detected events, and optimization of the logic is desirable. Pile-up was found to be of minor importance at typical mammography rates.

Place, publisher, year, edition, pages
2010. 156-162 p.
Keyword [en]
Spectral X-ray imaging, Mammography; Silicon strip detector, Photon counting, Energy resolution, Cascaded detector model
National Category
Electrical Engineering, Electronic Engineering, Information Engineering Medical Laboratory and Measurements Technologies Other Engineering and Technologies not elsewhere specified Radiology, Nuclear Medicine and Medical Imaging
Identifiers
URN: urn:nbn:se:kth:diva-11636DOI: 10.1016/j.nima.2009.10.152ISI: 000274772800023Scopus ID: 2-s2.0-77949279240OAI: oai:DiVA.org:kth-11636DiVA: diva2:278573
Note
QC 20100714Available from: 2009-11-27 Created: 2009-11-27 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Spectral Mammography with X-Ray Optics and a Photon-Counting Detector
Open this publication in new window or tab >>Spectral Mammography with X-Ray Optics and a Photon-Counting Detector
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Early detection is vital to successfully treating breast cancer, and mammography screening is the most efficient and wide-spread method to reach this goal. Imaging low-contrast targets, while minimizing the radiation exposure to a large population is, however, a major challenge. Optimizing the image quality per unit radiation dose is therefore essential. In this thesis, two optimization schemes with respect to x-ray photon energy have been investigated: filtering the incident spectrum with refractive x-ray optics (spectral shaping), and utilizing the transmitted spectrum with energy-resolved photon-counting detectors (spectral imaging).

Two types of x-ray lenses were experimentally characterized, and modeled using ray tracing, field propagation, and geometrical optics. Spectral shaping reduced dose approximately 20% compared to an absorption-filtered reference system with the same signal-to-noise ratio, scan time, and spatial resolution. In addition, a focusing pre-object collimator based on the same type of optics reduced divergence of the radiation and improved photon economy by about 50%.

A photon-counting silicon detector was investigated in terms of energy resolution and its feasibility for spectral imaging. Contrast-enhanced tumor imaging with a system based on the detector was characterized and optimized with a model that took anatomical noise into account. Improvement in an ideal-observer detectability index by a factor of 2 to 8 over that obtained by conventional absorption imaging was found for different levels of anatomical noise and breast density. Increased conspicuity was confirmed by experiment. Further, the model was extended to include imaging of unenhanced lesions. Detectability of microcalcifications increased no more than a few percent, whereas the ability to detect large tumors might improve on the order of 50% despite the low attenuation difference between glandular and cancerous tissue. It is clear that inclusion of anatomical noise and imaging task in spectral optimization may yield completely different results than an analysis based solely on quantum noise.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. x, 56 p.
Series
Trita-FYS, ISSN 0280-316X ; 2009:69
Keyword
mammography; x-ray optics; photon counting; spectral shaping; spectral imaging; collimation; radiation dose; signal-to-noise ratio; quantum noise; anatomical noise; spatial resolution; x-ray flux;
National Category
Engineering and Technology Other Engineering and Technologies Atom and Molecular Physics and Optics Other Engineering and Technologies not elsewhere specified Electrical Engineering, Electronic Engineering, Information Engineering Medical Laboratory and Measurements Technologies Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:kth:diva-11641 (URN)978-91-7415-516-7 (ISBN)
Public defence
2009-12-18, Kollegiesalen, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note
QC 20100714Available from: 2009-12-04 Created: 2009-11-27 Last updated: 2010-07-15Bibliographically approved

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Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
Electrical Engineering, Electronic Engineering, Information EngineeringMedical Laboratory and Measurements TechnologiesOther Engineering and Technologies not elsewhere specifiedRadiology, Nuclear Medicine and Medical Imaging

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