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AEC for scanning digital mammography based on variation of scan velocity
KTH, School of Engineering Sciences (SCI), Physics.
KTH, School of Engineering Sciences (SCI), Physics.
KTH, School of Engineering Sciences (SCI), Physics.
KTH, School of Engineering Sciences (SCI), Physics.ORCID iD: 0000-0002-3039-9791
2005 (English)In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 32, no 11, 3367-3374 p.Article in journal (Refereed) Published
Abstract [en]

A theoretical evaluation of nonuniform x-ray field distributions in mammography was conducted. An automatic exposure control (AEC) is proposed for a scanning full field digital mammography system. It uses information from the leading part of the detector to vary the scan velocity dynamically, thus creating a nonuniform x-ray field in the scan direction. Nonuniform radiation fields were also created by numerically optimizing the scan velocity profile to each breast's transmission distribution, with constraints on velocity and acceleration. The goal of the proposed AEC is to produce constant pixel signal-to-noise ratio throughout the image. The target pixel SNR for each image could be set based on the breast thickness, breast composition, and the beam quality as to achieve the same contrast-to-noise ratio between images for structures of interest. The results are quantified in terms of reduction in entrance surface air kerma (ESAK) and scan time relative to a uniform x-ray field. The theoretical evaluation was performed on a set of 266 mammograms. The performance of the different methods to create nonuniform fields decreased with increased detector width, from 18% to 11% in terms of ESAK reduction and from 30% to 25% in terms of scan time reduction for the proposed AEC and detector widths from 10 to 60 mm. Some correlation was found between compressed breast thickness and the projected breast area onto the image field. This translated into an increase of the ESAK and decrease of the scan time reduction with breast thickness. Ideally a nonuniform field in two dimensions could reduce the entrance dose by 39% on average, whereas a field nonuniform in only the scanning dimension ideally yields a 20% reduction. A benefit with the proposed AEC is that the risk of underexposing the densest region of the breast can be virtually eliminated.

Place, publisher, year, edition, pages
2005. Vol. 32, no 11, 3367-3374 p.
Keyword [en]
mammography; exposure control; scanning; slit; slot ; SCREEN-FILM MAMMOGRAPHY; REGIONAL EXPOSURE CONTROL; IMAGE QUALITY; FILTER COMBINATIONS; CHEST RADIOGRAPHY; MONTE-CARLO; SYSTEM; ANODE; CONTRAST; OPTIMIZATION
National Category
Medical Laboratory and Measurements Technologies
Identifiers
URN: urn:nbn:se:kth:diva-6938DOI: 10.1118/1.2089487ISI: 000233385800018Scopus ID: 2-s2.0-28044435613OAI: oai:DiVA.org:kth-6938DiVA: diva2:11793
Note
QC 20100825Available from: 2007-03-30 Created: 2007-03-30 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Digital Mammography with a Photon Counting Detector in a Scanned Multislit Geometry
Open this publication in new window or tab >>Digital Mammography with a Photon Counting Detector in a Scanned Multislit Geometry
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Mammography screening aims to reduce the number of breast cancer deaths by early detection of the disease, which is one of the leading causes of deaths for middle aged women in the western world. The risk from the x-ray radiation in mammography is relatively low but still a factor in the benefit-risk ratio of screening. The characterization and optimization of a digital mammography system is presented in this thesis. The investigated system is shown to be highly dose efficient by employing a photon counting detector in a scanning multislit geometry.

A novel automatic exposure control (AEC) is proposed and validated in clinical practise. The AEC uses the leading detector edge to measure the transmission of the breast. The exposure is modulated by altering the scan velocity during the scan. A W-Al anode-filter combination is proposed.

The characterization of the photon counting detector is performed using the detective quantum efficiency. The effect of the photon counting detector and the multislit geometry on the measurement method is studied in detail. It is shown that the detector has a zero-frequency DQE of over 70\% and that it is quantum limited even at very low exposures.

Efficient rejection of image-degrading secondary radiation is fundamental for a dose efficient system. The efficiency of the scatter rejection techniques currently used are quantified and compared to the multislit geometry.

A system performance metric with its foundation in statistical decision theory is discussed. It is argued that a photon counting multislit system can operate at approximately half the dose compared to several other digital mammography techniques.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. viii, 41 p.
Series
Trita-FYS, ISSN 0280-316X ; 2007:28
Keyword
mammography, digital, photon counting, scanning, detective quantum effciency, scattered radiation, automatic exposure control
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-4322 (URN)978-91-7178-622-7 (ISBN)
Public defence
2007-04-20, Sal F3, KTH, Lindstedtsvägen 26, Stockholm, 14:00
Opponent
Supervisors
Note
QC 20100825Available from: 2007-03-30 Created: 2007-03-30 Last updated: 2010-08-25Bibliographically approved

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