SA Journal of Radiology

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The relationship between compression force, image quality and radiation dose in mammography

A Korf, C Herbst, W Rae


Background. Mammography aims to obtain mammograms of the best possible image quality with the least possible radiation dose. 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 investigates 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) and compared with the allowable limit.                                                                                        Results. The geometry effect was not observed. An improvement in image quality with increased compression was found. Entrance dose decreased 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.

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