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A Framework for Evaluating Threshold Variation Compensation Methods in Photon Counting Spectral CT
KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.ORCID iD: 0000-0002-5092-8822
KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
2012 (English)In: IEEE Transactions on Medical Imaging, ISSN 0278-0062, E-ISSN 1558-254X, Vol. 31, no 10, 1861-1874 p.Article in journal (Refereed) Published
Abstract [en]

One of the challenges in the development of photon counting spectral computed tomography (CT) detectors is that the location of the energy thresholds tends to vary among detector elements. If not compensated for, this threshold variation leads to ring artifacts in the reconstructed images. In this paper, a framework is presented for the systematic comparison of different methods of compensating for inhomogeneities among detector elements in photon counting CT with multiple energy bins. Furthermore, we propose the use of an affine minimum mean square error estimator, calibrated against transmission measurements on different combinations of two materials, for inhomogeneity compensation. Using the framework developed here, this method is compared to two other compensation schemes, flatfielding using an air scan and signal-to-thickness calibration using a step wedge calibrator, in a simulation study. The results show that for all but the lowest studied level of threshold spread, the proposed method is superior to signal-to-thickness calibration, which in turn is superior to flatfielding. We also demonstrate that the effects of threshold variation can be countered to a large extent by substructuring each detector element into depth segments.

Place, publisher, year, edition, pages
2012. Vol. 31, no 10, 1861-1874 p.
Keyword [en]
Calibration, computed tomography (CT), homogeneity requirements, photon counting, ring artifacts, spectral computed tomography (CT)
National Category
Radiology, Nuclear Medicine and Medical Imaging
URN: urn:nbn:se:kth:diva-105664DOI: 10.1109/TMI.2012.2204274ISI: 000310149700003ScopusID: 2-s2.0-84867086955OAI: diva2:571750

QC 20121123

Available from: 2012-11-23 Created: 2012-11-23 Last updated: 2016-05-20Bibliographically approved
In thesis
1. Spectral Computed Tomography with a Photon-Counting Silicon-Strip Detector
Open this publication in new window or tab >>Spectral Computed Tomography with a Photon-Counting Silicon-Strip Detector
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Computed tomography (CT) is a widely used medical imaging modality. By rotating an x-ray tube and an x-ray detector around the patient, a CT scanner is able to measure the x-ray transmission from all directions and form an image of the patient’s interior. CT scanners in clinical use today all use energy-integrating detectors, which measure the total incident energy for each measurement interval. A photon-counting detector, on the other hand, counts the number of incoming photons and can in addition measure the energy of each photon by comparing it to a number of energy thresholds. Using photon- counting detectors in computed tomography could lead to improved signal-to-noise ratio, higher spatial resolution and improved spectral imaging which allows better visualization of contrast agents and more reliable quantitative measurements. In this Thesis, the feasibility of using a photon-counting silicon-strip detector for CT is investigated. In the first part of the Thesis, the necessary performance requirements on such a detector is investigated in two different areas: the detector element homogeneity and the capability of handling high photon fluence rates. A metric of inhomogeneity is proposed and used in a simulation study to evaluate different inhomogeneity compensation methods. Also, the photon fluence rate incident on the detector in a scanner in clinical use today is investigated for different patient sizes through dose rate measurements together with simulations of transmission through patient im- ages. In the second part, a prototype detector module is used to demonstrate new applications enabled by the energy resolution of the detector. The ability to generate material-specific images of contrast agents with iodine and gadolinium is demonstrated. Furthermore, it is shown theoretically and ex- perimentally that interfaces in the image can be visualized by imaging the so-called nonlinear partial volume effect. The results suggest that the studied silicon-strip detector is a promising candidate for photon-counting CT.  

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 43 p.
TRITA-FYS, ISSN 0280-316X ; 2016:20
Photon-counting, silicon-strip detector, spectral computed tomography, ring artifacts, fluence rate, basis material decomposition, sub-pixel information
National Category
Other Physics Topics Medical Equipment Engineering
Research subject
urn:nbn:se:kth:diva-187263 (URN)978-91-7595-991-7 (ISBN)
Public defence
2016-06-14, FR4, Roslagstullsbacken 21, AlbaNova Universitetscentrum, Stockholm, 09:00 (English)
Available from: 2016-05-20 Created: 2016-05-18 Last updated: 2016-05-20Bibliographically approved

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