Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Characterization and Optimization of Silicon-strip Detectors for Mammography and Computed Tomography
KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging. (Physics of Medical imaging)ORCID iD: 0000-0001-8560-3262
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The goal in medical x-ray imaging is to obtain the image quality requiredfor a given detection task, while ensuring that the patient dose is kept as lowas reasonably achievable. The two most common strategies for dose reductionare: optimizing incident x-ray beams and utilizing energy informationof transmitted beams with new detector techniques (spectral imaging). Inthis thesis, dose optimization schemes were investigated in two x-ray imagingsystems: digital mammography and computed tomography (CT).

In digital mammography, the usefulness of anti-scatter grids was investigatedas a function of breast thickness with varying geometries and experimentalconditions. The general conclusion is that keeping the grid is optimalfor breasts thicker than 5 cm, whereas the dose can be reduced without a gridfor thinner breasts.

A photon-counting silicon-strip detector developed for spectral mammographywas characterized using synchrotron radiation. Energy resolution, ΔE/Ein, was measured to vary between 0.11-0.23 in the energy range 15-40 keV, which is better than the energy resolution of 0.12-0.35 measured inthe state-of-the-art photon-counting mammography system. Pulse pileup hasshown little effect on energy resolution.

In CT, the performance of a segmented silicon-strip detector developedfor spectral CT was evaluated and a theoretical comparison was made withthe state-of-the-art CT detector for some clinically relevant imaging tasks.The results indicate that the proposed photon-counting silicon CT detector issuperior to the state-of-the-art CT detector, especially for high-contrast andhigh-resolution imaging tasks.

The beam quality was optimized for the proposed photon-counting spectralCT detector in two head imaging cases: non-enhanced imaging and Kedgeimaging. For non-enhanced imaging, a 120-kVp spectrum filtered by 2half value layer (HVL) copper (Z = 29) provides the best performance. Wheniodine is used in K-edge imaging, the optimal filter is 2 HVL iodine (Z = 53)and the optimal kVps are 60-75 kVp. In the case of gadolinium imaging, theradiation dose can be minimized at 120 kVp filtered by 2 HVL thulium (Z =69).

Place, publisher, year, edition, pages
STOCKHOLM: KTH Royal Institute of Technology, 2016. , viii, 73 p.
Series
TRITA-FYS, ISSN 0280-316X ; 0280-316X
Keyword [en]
mammography, anti-scatter grid, photon-counting, spectral computed tomography, silicon strip, ASIC, energy resolution, Compton scatter, material decomposition, K-edge imaging
National Category
Medical Engineering
Research subject
Medical Technology
Identifiers
URN: urn:nbn:se:kth:diva-184092ISBN: 978-91-7595-919-1 (print)OAI: oai:DiVA.org:kth-184092DiVA: diva2:914033
Public defence
2016-04-22, FA 31, ROSLAGSTULLSBACKEN 21, KTH, STOCKHOLM, 09:00 (English)
Opponent
Supervisors
Note

QC 20160401

Available from: 2016-04-01 Created: 2016-03-23 Last updated: 2016-04-01Bibliographically approved
List of papers
1. On image quality metrics and the usefulness of grids in digital mammography
Open this publication in new window or tab >>On image quality metrics and the usefulness of grids in digital mammography
2015 (English)In: Journal of medical imaging (Bellingham, Wash.), ISSN 2329-4302, Vol. 2, no 1, 013501-013501 p.Article in journal (Refereed) Published
Abstract [en]

Antiscatter grids are used in digital mammography to reduce the scattered radiation from the breast and improve image contrast. They are, however, imperfect and lead to partial absorption of primary radiation, as well as failing to absorb all scattered radiation. Nevertheless, the general consensus has been that antiscatter grids improve image quality for the majority of breast types and sizes. There is, however, inconsistency in the literature, and recent results show that a substantial image quality improvement can be achieved even for thick breasts if the grid is disposed of. The purpose of this study was to investigate if differences in the considered imaging task and experimental setup could explain the different outcomes. We estimated the dose reduction that can be achieved if the grid were to be removed as a function of breast thickness with varying geometries and experimental conditions. Image quality was quantified by the signal-difference-to-noise ratio (SDNR) measured using an aluminum (Al) filter on blocks of poly(methyl methacrylate) (PMMA), and images were acquired with and without grid at a constant exposure. We also used a theoretical model validated with Monte Carlo simulations. Both theoretically and experimentally, the main finding was that when a large [Formula: see text] Al filter was used, the SDNR values for the gridless images were overestimated up to 25% compared to the values for the small [Formula: see text] filter, and gridless imaging was superior for any PMMA thickness. For the small Al filter, gridless imaging was only superior for PMMAs thinner than 4cm. This discrepancy can be explained by a different sensitivity to and sampling of the angular scatter spread function, depending on the size of the contrast object. The experimental differences were eliminated either by using a smaller region of interest close to the edge of the large filter or by applying a technique of scatter correction by subtracting the estimated scatter image. These results explain the different conclusions reported in the literature and show the importance of the selection of measurement methods. Since the interesting structures in mammography are below the 1-cm scale, we advocate the use of smaller contrast objects for assessment of antiscatter grid performance.

Place, publisher, year, edition, pages
Society of Photo-Optical Instrumentation Engineers, 2015
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-171173 (URN)10.1117/1.JMI.2.1.013501 (DOI)000366848500001 ()26158077 (PubMedID)2-s2.0-85019274989 (Scopus ID)
Note

QC 20160121

Available from: 2015-07-20 Created: 2015-07-20 Last updated: 2017-10-31Bibliographically approved
2. A photon-counting silicon-strip detector for digital mammography with an ultrafast 0.18-mu m CMOS ASIC
Open this publication in new window or tab >>A photon-counting silicon-strip detector for digital mammography with an ultrafast 0.18-mu m CMOS ASIC
Show others...
2014 (English)In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 749, 1-6 p.Article in journal (Refereed) Published
Abstract [en]

We have evaluated a silicon-strip detector with a 0.18-mu m CMOS application specific integrated circuits (ASIC) containing 160 channels for use in photon-counting digital mammography. Measurements were performed at the Elettra light source using monochromatic X-ray beams with different energies and intensities. Energy resolution, Delta E/E-in, was measured to vary between 0.10 and 0.23 in the energy range of 15-40 keV. Pulse pileup has shown little effect on energy resolution.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Mammography, Charge sharing, ASIC, Energy resolution
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:kth:diva-145253 (URN)10.1016/j.nima.2014.02.033 (DOI)000334075000001 ()2-s2.0-84896521372 (Scopus ID)
Note

QC 20140516

Available from: 2014-05-16 Created: 2014-05-15 Last updated: 2017-12-05Bibliographically approved
3. Optimization Of Beam Quality For Photon-Counting Spectral Computed Tomography In Head Imaging: Simulation Study
Open this publication in new window or tab >>Optimization Of Beam Quality For Photon-Counting Spectral Computed Tomography In Head Imaging: Simulation Study
2015 (English)In: Journal of Medical Imaging, ISSN 2329-4302, E-ISSN 2329-4310, Vol. 2, no 4, 043504-1-043504-16 p., 043504Article in journal (Refereed) Published
Abstract [en]

Head computed tomography (CT) plays an important role in the comprehensive evaluation of acutestroke. Photon-counting spectral detectors, as promising candidates for use in the next generation of x-ray CTsystems, allow for assigning more weight to low-energy x-rays that generally contain more contrast information.Most importantly, the spectral information can be utilized to decompose the original set of energy-selectiveimages into several basis function images that are inherently free of beam-hardening artifacts, a potential ad-vantage for further improving the diagnosis accuracy. We are developing a photon-counting spectral detector forCT applications. The purpose of this work is to determine the optimal beam quality for material decomposition intwo head imaging cases: nonenhanced imaging and K-edge imaging. A cylindrical brain tissue of 16-cm diam-eter, coated by a 6-mm-thick bone layer and 2-mm-thick skin layer, was used as a head phantom. The imagingtarget was a 5-mm-thick blood vessel centered in the head phantom. In K-edge imaging, two contrast agents,iodine and gadolinium, with the same concentration (5mg∕mL) were studied. Three parameters that affect beamquality were evaluated: kVp settings (50 to 130 kVp), filter materials (Z¼13to 83), and filter thicknesses [0 to 2half-value layer (HVL)]. The image qualities resulting from the varying x-ray beams were compared in terms oftwo figures of merit (FOMs): squared signal-difference-to-noise ratio normalized by brain dose (SDNR2∕BD) andthat normalized by skin dose (SDNR2∕SD). For nonenhanced imaging, the results show that the use of the 120-kVp spectrum filtered by 2 HVL copper (Z¼29) provides the best performance in both FOMs. When iodine isused in K-edge imaging, the optimal filter is 2 HVL iodine (Z¼53) and the optimal kVps are 60 kVp in terms ofSDNR2∕BD and 75 kVp in terms of SDNR2∕SD. A tradeoff of 65 kVp was proposed to lower the potential riskof skin injuries if a relatively long exposure time is necessarily performed in the iodinated imaging. In the case ofgadolinium imaging, both SD and BD can be minimized at 120 kVp filtered with 2 HVL thulium (Z¼69). Theresults also indicate that with the same concentration and their respective optimal spectrum, the values ofSDNR2∕BD and SDNR2∕SD in gadolinium imaging are, respectively, around 3 and 10 times larger thanthose in iodine imaging. However, since gadolinium is used in much lower concentrations than iodine in theclinic, iodine may be a preferable candidate for K-edge imaging.

Place, publisher, year, edition, pages
SPIE, 2015
Keyword
photon counting, spectral computed tomography, material decomposition, K-edge imaging
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:kth:diva-184602 (URN)10.1117/1.JMI.2.4.043504 (DOI)000374235100015 ()
Note

QC 20160401

Available from: 2016-04-01 Created: 2016-04-01 Last updated: 2017-11-30Bibliographically approved
4. Size-dependent scanning parameters (kVp and mAs) for photon-counting spectral CT system in pediatric imaging: simulation study
Open this publication in new window or tab >>Size-dependent scanning parameters (kVp and mAs) for photon-counting spectral CT system in pediatric imaging: simulation study
2016 (English)In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 61, no 11Article in journal (Refereed) Published
Abstract [en]

We are developing a photon-counting spectral CT detector with small pixel size of 0.40.5 mm2, o ering a potentialadvantage for better visualization of small structures in pediatric patients. The purpose of this study is to determinethe patient size dependent scanning parameters (kVp and mAs) for pediatric CT in two imaging cases: adipose imagingand iodinated blood imaging.Cylindrical soft-tissue phantoms of diameters between 10-25 cm were used to mimic patients of di erent ages from 0-15 y. For adipose imaging, a 5-mm-diameter adipose sphere was assumed as an imaging target, while an iodinated bloodsphere of 1 mm in diameter was assumed in the case of iodinated imaging. By applying the geometry of a commercial CTscanner (GE LightSpeed VCT), simulations were carried out to calculate the detectability index,d02, with tube potentialsvarying from 40 to 140 kVp. The optimal kVp for each phantom in each imaging case was determined such that the dose-normalized detectability index,d02=dose, is maximized. With the assumption that image quality in pediatric imagingis required the same as in typical adult imaging, the value of mAs at optimal kVp for each phantom was selected toachieve a reference detectability index that was obtained by scanning an adult phantom (30 cm in diameter) in a typicaladult CT procedure (120 kVp and 200 mAs) using a modeled energy-integrating system.For adipose imaging, the optimal kVps are 50, 60, 80, and 120 kVp, respectively, for phantoms of 10, 15, 20, and25-cm in diameter. The corresponding mAs values required to achieve the reference detectability index are only 9%,23%, 24%, and 54% of the mAs that is used for adult patients at 120 kVp, for 10, 15, 20, and 25-cm-diameter phantoms,respectively. In the case of iodinated imaging, a tube potential of 60 kVp was found optimal for all phantoms investigated,and the mAs values required to achieve the reference detectability index are 2%, 9%, 37%, and 109% of the adult mAs.The results also indicate that with the use of respective optimal kVps, the photon-counting spectral system o ers up to30% higherd02=dose than the modeled energy-integrating system for adipose imaging, and 70% for iodinated imaging.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2016
Keyword
photon counting, spectral CT, silicon-strip detector, pediatric imaging, detectability index
National Category
Radiology, Nuclear Medicine and Medical Imaging
Identifiers
urn:nbn:se:kth:diva-184605 (URN)10.1088/0031-9155/61/11/4105 (DOI)000377427700014 ()2-s2.0-84971515147 (Scopus ID)
Note

QC 20160706

Available from: 2016-04-01 Created: 2016-04-01 Last updated: 2017-11-30Bibliographically approved

Open Access in DiVA

fulltext(10581 kB)146 downloads
File information
File name FULLTEXT01.pdfFile size 10581 kBChecksum SHA-512
9270794fbeb12a17216366f1a8bdbb0d9f7de9a7256a3d13eac3a97ec12f893d136c218799e9cccfbb5677e6ae352280be8e77f2d88364b413f4ef53c9c4b73f
Type fulltextMimetype application/pdf

Authority records BETA

Chen, Han

Search in DiVA

By author/editor
Chen, Han
By organisation
Physics of Medical Imaging
Medical Engineering

Search outside of DiVA

GoogleGoogle Scholar
Total: 146 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

isbn
urn-nbn

Altmetric score

isbn
urn-nbn
Total: 322 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf