Inferring the Breast Periphery from an Image When Measuring Volumetric Breast Density

Abstract

Breast density is a key component of risk assessment for personalised screening, necessitating robust, repeatable measures. The Standard Attenuation Rate (SAR) enables the quantification of breast tissue radiodensity at each pixel, relative to the attenuation of a reference material, so may be used as a measure of volumetric breast density. A major complication is quantification of tissue in the periphery of the breast, the (often substantial) region between the skin boundary and the point at which the breast occupies the entire distance between the plates, since the thickness is governed by the shape of the compressed breast, rather than the separation of the plates. We present a method to measure the compressed shape from the image, hence the thickness at each point in the periphery. The method exploits the vastly different attenuation of the various breast tissues from that of air, and uses spatial smoothing to glean a signal estimating solely the underlying thickness. An iterative refinement procedure allows for variation in scatter in the periphery arising from the air boundary edge effects. The outcome of the inclusion of the periphery in breast density quantified by this method is analysed, and the importance of this region’s inclusion illustrated.