Abstract
Background. Mammography aims to obtain mammograms of best possible image quality with least possible radiation dose.1 Theoretically, an increase in breast compression gives a reduction in thickness, without changing the density, resulting in improved image quality and reduced radiation dose. 
 Aim. This study aims to investigate the relationship between compression force, phantom thickness, image quality and radiation dose. The existence of a compression point beyond which increased compression gives a change in density rather than thickness is also considered.
 Method. Image quality is assessed with a contrast-detail phantom within Superflab phantom on a computed radiography (CR) mammography unit using automatic exposure control (AEC). Image quality is determined by visual inspection and image quality figure (IQF) scoring. The effect of compression and lesion depth on image quality is determined. Entrance and exit doses are calculated. The relationship between entrance dose, compression and thickness is investigated, as is the existence of a compression point beyond which a change in phantom density occurs. The average glandular dose (AGD) is calculated from the scanning average level (SAL) and logarithmic mean (LgM) according to Koen et al,2 and compared to the allowable limit. 
 Results. The geometry effect was not observed. An improvement in image quality with increased compression was found. Entrance dose did decrease with increased compression. This trend was not observed with exit dose as AEC was used and exit dose was calculated from SAL values. The “change-in-density” point of compression was determined. Both LgM and SAL could be used successfully for AGD calculation.
Highlights
Entrance dose decreased with increased compression. This trend was not observed with exit dose as automatic exposure control (AEC) was used and exit dose was calculated from scanning average level (SAL)
The main method of achieving increased image quality and reduced radiation dose is by compression, which spreads out overlapping tissues,[1] gives immobilisation of the breast and decreases exposure time, reducing movement
The results for entrance and exit dose calculation are shown in Table
Summary
The main method of achieving increased image quality and reduced radiation dose is by compression, which spreads out overlapping tissues,[1] gives immobilisation of the breast and decreases exposure time, reducing movement. It decreases breast thickness, whereby the breast dose is reduced. According to Poulos et al.,[3,4] there exists a point beyond which an increase in compression of the breast does not give spreading of the tissues but rather a change in breast density. An increase in breast compression gives a reduction in thickness without changing the density, resulting in improved image quality and reduced radiation dose
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