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An efficient pre-object collimator based on an x-ray lens
KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging. (Medical Imaging)
KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging. (Medical Imaging)
KTH, School of Engineering Sciences (SCI), Physics.
KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging. (Medical Imaging)ORCID iD: 0000-0002-7725-0548
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2009 (English)In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 36, no 2, 626-633 p.Article in journal (Refereed) Published
Abstract [en]

A multiprism lens (MPL) is a refractive x-ray lens with one-dimensional focusing properties. If used as a pre-object collimator in a scanning system for medical x-ray imaging, it reduces the divergence of the radiation and improves on photon economy compared to a slit collimator. Potential advantages include shorter acquisition times, a reduced tube loading, or improved resolution. We present the first images acquired with a MPL in a prototype for a scanning mammography system. The lens showed a gain of flux of 1.32 compared to a slit collimator at equal resolution, or a gain in resolution of 1.31–1.44 at equal flux. We expect the gain of flux in a clinical setup with an optimized MPL and a custom-made absorption filter to reach 1.67, or 1.45–1.54 gain in resolution.

Place, publisher, year, edition, pages
2009. Vol. 36, no 2, 626-633 p.
Keyword [en]
x-ray imaging, mammography, x-ray optics, multiprism lens, collimation, x-ray flux, acquisition time, resolution
National Category
Other Engineering and Technologies not elsewhere specified Atom and Molecular Physics and Optics Radiology, Nuclear Medicine and Medical Imaging Medical Laboratory and Measurements Technologies
Identifiers
URN: urn:nbn:se:kth:diva-11634DOI: 10.1118/1.3062926ISI: 000262852600037Scopus ID: 2-s2.0-59249085647OAI: oai:DiVA.org:kth-11634DiVA: diva2:278565
Note
QC 20100713Available 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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Publisher's full textScopushttp://dx.doi.org/10.1118/1.3062926

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Nillius, Peter

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