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
On image quality metrics and the usefulness of grids in digital mammography
KTH, School of Engineering Sciences (SCI), Physics.
KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.ORCID iD: 0000-0002-3039-9791
KTH, School of Engineering Sciences (SCI), Physics.
KTH, School of Engineering Sciences (SCI), Physics.
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. Vol. 2, no 1, 013501-013501 p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-171173DOI: 10.1117/1.JMI.2.1.013501ISI: 000366848500001PubMedID: 26158077Scopus ID: 2-s2.0-85019274989OAI: oai:DiVA.org:kth-171173DiVA: diva2:842374
Note

QC 20160121

Available from: 2015-07-20 Created: 2015-07-20 Last updated: 2017-10-31Bibliographically approved
In thesis
1. Characterization and Optimization of Silicon-strip Detectors for Mammography and Computed Tomography
Open this publication in new window or tab >>Characterization and Optimization of Silicon-strip Detectors for Mammography and Computed Tomography
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
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:nbn:se:kth:diva-184092 (URN)978-91-7595-919-1 (ISBN)
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

Open Access in DiVA

No full text

Other links

Publisher's full textPubMedScopus

Search in DiVA

By author/editor
Chen, HanDanielsson, MatsXu, ChengCederström, Björn
By organisation
PhysicsPhysics of Medical Imaging
Physical Sciences

Search outside of DiVA

GoogleGoogle Scholar

doi
pubmed
urn-nbn

Altmetric score

doi
pubmed
urn-nbn
Total: 56 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