A statistical alternative to current measures of image quality in digital mammography

• Published in: Physics in medicine & biology Vol. 67; no. 3; pp. 35009 - 35023
• Main Authors: Caldwell, D, Baldelli, P, Phelan, N, Kenny, P
• Format: Journal Article
• Language: English
• Published: England IOP Publishing 07.02.2022
• Subjects: Breast; detectability index; image quality; low contrast detectability; Mammography - methods; mammography physics; NPWE model observer; Phantoms, Imaging; Quality Control; Radiographic Image Enhancement - methods; low contrast detectability; image quality; mammography physics; NPWE model observer; detectability index
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/1361-6560/ac4c2d

. Mammogram image quality in European breast screening systems is defined by threshold gold thickness ( ) assessment of the CDMAM contrast-detail phantom. Previous studies have outlined several limitations of the phantom including expense, number of images required and inter-phantom manufacturing variability. Two alternative approaches to image quality assessment for routine quality control are examined and compared to the CDMAM technique: (i) A detectability index ( ') based on a non-prewhitened model observer with an eye filter (NPWE) an (ii) A statistical estimate of contrast based on image noise levels ( ). . The ' calculation follows a previously published methodology based on the NNPS and contrast, both measured from an image of 5 cm of PMMA containing a 0.2 mm Al target, as well as the MTF measured under standard conditions. For the proposed statistical method, pixels in the centre of the same NNPS image were re-binned into a range of equivalent CDMAM target areas. For any area, the minimum contrast necessary to distinguish a signal from the background, , is 3.29 at a 95% level of confidence, where is the standard deviation of the background pixels. Theoretical analysis predicts a simple relationships between , and '. Measured values of were compared to and ' as a function of air kerma at the detector for ten digital mammography systems from three different manufacturers. . Theoretical relationships between ' and were demonstrated. Minimum acceptable image quality performance for 0.10 and 0.25 mm diameter discs, defined by the European Guidelines in terms of , are equivalent to ' values of 0.85 and 5.36 and threshold values of 0.055 and 0.022. . Strong correlations between log( ), log( ') and log( ) suggest that either alternative approach produces information corresponding to that obtained using the CDMAM. should be considered as a simple, objective and cost-effective alternative to routine image quality assessment in mammography.