Evaluation of the CDMAM phantom in the determination of the contrast-detail threshold thickness in a digital mammography system

Lado, L.; Piñeiro, C.; Otero, Carlos Názara; Sánchez, María Guadalupe; Medina, Esau; Pombar, M.

doi:10.1016/s1120-1797(22)00473-2

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“…Errors associated with manufacturing reproducibility mean that 'identical' phantoms can give varying threshold thickness results. Using different CDMAM phantoms under identical exposure conditions, Lado et al (2021) found variations in threshold gold thicknessof up to 23% for the 0.10 mm disc. The same study demonstrates the aforementioned reproducibilityissues associated with the CDMAM, with two setsof identical exposures of the same CDMAM phantom showing differences of up to 1.566 μm (percentage difference of 52.9%) for the threshold thickness of 0.10 mm discs.…”

Section: Discussionmentioning

confidence: 91%

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

Caldwell¹,

Baldelli²,

Phelan³

et al. 2022

Phys. Med. Biol.

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Objective: Mammogram image quality in Europe is defined by threshold gold thickness (T) assessment of the CDMAM contrast-detail phantom. Several limitations of the phantom exist 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 (d’) based on a non-prewhitened model observer with an eye filter and (ii) A statistical estimate of contrast based on image noise levels (CSTAT). Approach: The d’ calculation follows previously published methodology based on the NNPS and contrast, both measured from an image of 5cm of PMMA containing a 0.2mm Al target, as well as the MTF measured under standard conditions. For the 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, CSTAT, is 3.29σ at a 95% level of confidence, where σ is the standard deviation of the background pixels. Theoretical analysis predicts simple relationships between CSTAT, T and d’. Measured values of CSTAT were compared to T and d’ as a function of air kerma at the detector for ten mammography systems from three manufacturers. Main Results: Theoretical relationships between CSTAT, d’ and T were demonstrated. Minimum acceptable image quality performance for 0.10 and 0.25 mm diameter discs, defined by the European Guidelines in terms of T, are equivalent to d’ values of 0.85 and 5.36 and threshold CSTAT values of 0.055 and 0.022. Significance: Strong correlations between log(T), log(d’) and log(CSTAT) suggest that either alternative approach produces information corresponding to that obtained using the CDMAM. CSTAT should be considered as a simple, objective and cost-effective alternative to routine image quality assessment in mammography.

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Section: Discussionmentioning

confidence: 91%