Procedure for quantitatively assessing automatic exposure control in mammography: a study of the GE Senographe 600 TS
S Meeson, PhD1,,
K C Young, PhD1,
P B Hollaway, MSc2 and
M G Wallis, FRCR3
1National Co-ordinating Centre for the Physics of Mammography and 2Regional Radiation Protection Service, Department of Medical Physics, St Luke's Wing, Royal Surrey County Hospital, Guildford GU2 7XX, and 3Warwickshire, Solihull & Coventry Breast Screening Centre, Coventry and Warwickshire Hospital, Stoney Stanton Road, Coventry CV1 4FH, UK
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Figure 1. Plan of the breast support table (not to scale) showing where the test blocks were positioned for the exposure measurements. The shaded area corresponds to the area of the support table that was covered when the rectangular test object was placed 160 mm from the chest wall edge of the support table. The positions of the test object when placed 40 mm, 80 mm and 120 mm from the chest wall edge of the support table are also indicated. When semi-circular blocks were used, the distance from the chest wall was measured to the furthest point on the semi-circle.
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Figure 2. The three possible regions of interest corresponding to the automatic exposure control detector positions are shown on the mammogram images of women with predominantly adipose (a) and dense glandular (b) breast tissues.
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Figure 3. Relationship between the width of the test object and the normalized exposure for four different GE 600 TS systems.
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Figure 4. Relationship between the mean optical density (OD) in the main breast region of interest (ROI) and the area of the main breast ROI. The position of the automatic exposure control detector used clinically is indicated by the data point symbol.
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Figure 5. Relationship between the mean optical density (OD) in the region of interest (ROI) corresponding to the automatic exposure control (AEC) detector position and the area of the main breast ROI. The position of the AEC detector used clinically is indicated by the data point symbol. The corresponding ODs for a semi-circular block of PMMA are shown as a solid curve. The PMMA data are from a different X-ray system (X-ray set 1) and are shown together with the clinical data to demonstrate the similarity in the shape of the relationship between the mean OD in the ROI corresponding to the AEC detector position and the area of the main breast.
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Copyright © 2001 by the British Institute of Radiology.
