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A Tunable Energy Filter for Medical X-Ray Imaging
KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging. (Medical Imaging)
KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging. (Medical Imaging)
Uppsala universitet. (Department of Engineering Sciences)
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2008 (English)In: X-Ray Optics and Instrumentation, ISSN 1687-7632, Vol. 2008Article in journal (Refereed) Published
Abstract [en]

A multiprism lens (MPL) is a refractive X-ray lens, and its chromatic properties can be employed in an energy filtering setup to obtain a narrow tunable X-ray spectrum. We present the first evaluation of such a filter for medical X-ray imaging. The experimental setup yields a 6.6 gain of flux at 20 keV, and we demonstrate tunability by altering the energy spectrum to center also around 17 and 23 keV. All measurements are found to agree well with ray-tracing and a proposed geometrical model. Compared to a model mammography system with absorption filtering, the experimental MPL filter reduces dose 13–25% for 3–7 cm breasts if the spectrum is centered around the optimal energy. Additionally, the resolution is improved 2.5 times for a 5 cm breast. The scan time is increased 3 times but can be reduced with a slightly decreased energy filtering and resolution.

Place, publisher, year, edition, pages
Hindawi , 2008. Vol. 2008
Keyword [en]
x-ray imaging, mammography, x-ray optics, multiprism lens, energy filtering, radiation dose
National Category
Other Engineering and Technologies not elsewhere specified Medical Laboratory and Measurements Technologies Radiology, Nuclear Medicine and Medical Imaging Atom and Molecular Physics and Optics
Identifiers
URN: urn:nbn:se:kth:diva-11633DOI: 10.1155/2008/635024OAI: oai:DiVA.org:kth-11633DiVA: diva2:278564
Note
QC 20100713Available from: 2009-11-27 Created: 2009-11-27 Last updated: 2010-07-15Bibliographically 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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