Image quality assessment in digital mammography: part II. NPWE as a validated alternative for contrast detail analysis

Abstract

Assessment of image quality for digital x-ray mammography systems used in European screening programs relies mainly on contrast-detail CDMAM phantom scoring and requires the acquisition and analysis of many images in order to reduce variability in threshold detectability. Part II of this study proposes an alternative method based on the detectability index (d') calculated for a non-prewhitened model observer with an eye filter (NPWE). The detectability index was calculated from the normalized noise power spectrum and image contrast, both measured from an image of a 5 cm poly(methyl methacrylate) phantom containing a 0.2 mm thick aluminium square, and the pre-sampling modulation transfer function. This was performed as a function of air kerma at the detector for 11 different digital mammography systems. These calculated d' values were compared against threshold gold thickness (T) results measured with the CDMAM test object and against derived theoretical relationships. A simple relationship was found between T and d', as a function of detector air kerma; a linear relationship was found between d' and contrast-to-noise ratio. The values of threshold thickness used to specify acceptable performance in the European Guidelines for 0.10 and 0.25 mm diameter discs were equivalent to threshold calculated detectability indices of 1.05 and 6.30, respectively. The NPWE method is a validated alternative to CDMAM scoring for use in the image quality specification, quality control and optimization of digital x-ray systems for screening mammography.

Implementation of a channelized Hotelling observer model to assess image quality of x-ray angiography systems

“…[1][2][3][4][5][6][7][8][9][10][11][12] The objectives of these studies are to (1) assist computer aided diagnosis systems in chest radiography and mammography, 1,2 (2) optimize dose, 7,12 (3) compare model results with conventional Fourier domain metrics, 3,6,10,11 and (4) evaluate the performance of digital mammography systems in the spatial 5 and Fourier domains. 8,9 Many of these investigations relied on simulated data, 4,6,7,[10][11][12] or a Fourier-based metric, 3,4,8,9 which requires assumptions that do not necessarily reflect actual digital x-ray systems. 6,10,11 Additionally, application of linear observer models to fluoroscopic and angiographic imaging systems has been investigated.…”

A comprehensive model for x-ray projection imaging system efficiency and image quality characterization in the presence of scattered radiation

“…The effect of scatter in the observer model may be taken into account in two ways: (1) using the presampling MTF (including the detector and focal spot blurs) along to the absolute object contrast (signal difference ΔP out ) and NPS (both measured on the images with scatter) (equation (23a)) or (2) using the system MTF (MTF sys ) along to the normalized object contrast (ΔP out /P out ) and NNPS, all three measured with scatter (equation (23b)). Both methods have been used in the literature: Monnin et al (2011) used the presampling MTF, while Liu et al (2014) used generalized MTF and NNPS in their observer model. The latter study showed the equivalence of the two approaches.…”

Radiation Doses and Risks Associated with Mammographic Screening

“…Different degrees of sophistication are possible: mathematical objects versus irregular shapes, homogenous backgrounds versus clustered lumpy backgrounds and even patient images, the choice of eye filter, etc. In selected studies, a correlation between the results of mathematical observers and the more simple contrast detail data could be shown [51]. Detectability d' can be used across systems.…”