A Statistical Method for Low Contrast Detectability Assessment in Digital Mammography
This study proposes a method to estimate low contrast detectability (LCD) applying a statistical method, based on the analysis of a uniform region. A dedicated test object was designed, made up of an acetate sheet equipped with a central uniform insert an
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Medical Physics Department, San Gerardo Hospital, ASST Monza, Monza, Italy 2 University of Milan, Milan, Italy [email protected] 3 Medical Physics Department, Bolzano Hospital, Bolzano, Italy
Abstract. This study proposes a method to estimate low contrast detectability (LCD) applying a statistical method, based on the analysis of a uniform region. A dedicated test object was designed, made up of an acetate sheet equipped with a central uniform insert and an aluminium step wedge, allowing linear conversion from pixel values to millimeters of aluminium. A Matlab program for automated image analysis was developed. Phantom images were acquired on two different digital mammography systems. Reproducibility and sensitivity to exposure variations of the proposed method were investigated for different dose levels. Further the impact of scattering and attenuation on LCD was studied adding PMMA layers of variable thickness (2 to 7 cm) upon the acetate sheet during exposure in automatic exposure control modality. The statistical method turned out to be a reliable and rapid method for LCD evaluation. Applications include routine assessment of equipment performance for digital mammography systems.
Keywords: Low constrast detectability Quality assurance
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Digital mammography
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Introduction
Performance assessment of digital mammography systems is commonly achieved using image quality metrics such as MTF (Modulation Transfer Function), NNPS (Normalised Noise Power Spectrum) and DQE (Detective Quantum Efficiency). These metrics provide a widely accepted method of characterising the physical performance of detector systems, but they generally do not include other fundamental elements of the imaging chain, such as scatter radiation. To provide a quantitative measure of image quality (IQ), low contrast detectability (LCD) is a fundamental parameter to be taken into account. Thus, the routine assessment and control of IQ is often evaluated in terms of threshold contrast visibility of details varying in diameter and contrast. Contrast detail curves, c Springer International Publishing Switzerland 2016 A. Tingberg et al. (Eds.): IWDM 2016, LNCS 9699, pp. 532–539, 2016. DOI: 10.1007/978-3-319-41546-8 67
A Statistical Method for Low Contrast Detectability
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displaying the minimum detected contrast for each detail diameter, are commonly used for reporting. A widespread phantom for IQ performance assessment of full field mammography systems is the CDMAM phantom (Artinis Medical Systems, The Netherlands). It embeds gold discs of 0.03–20 µm thickness and 0.06–2.00 mm diameter and is sandwiched between PMMA layers of variable thickness during image acquisition. Software packages have been developed in order to perform automated quantitative analysis of images produced with the CDMAM test object, in compliance with the European Guidelines Recommendations [1]. According to these recommendations, to increase reproducibility at least 16 CDMAM phantom images are required for each evaluation. This study proposes a method, based on sta
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