Breast tissue density measure

A method of processing a mammogram image which includes a nipple and a chest wall to derive a value for a parameter useful in detecting differences in breast tissue in subsequent images of the same breast or relative to a control group of such images, said derived parameter being a parameter that changes alongside changes in breast density, the method comprising the steps of processing an image of at least part of a breast by:

• calculating in a suitably programmed computer for pixels of the image respective coordinates by a method comprising for each point for which a set of coordinates is desired computing a first coordinate value s and a second coordinate value φ defining the position of said point in a coordinate system (s, φ) wherein said coordinate system comprises a set of curves diverging from an apex point set at said nipple and lying on a reference line which extends in a reference direction, each curve in said set of curves extending to intersect a base line set generally to follow said chest wall and extending from a first point to a second point,
• said first coordinate s representing a measure of a geodesic distance from said apex point along one said curve which contains said point, and said second coordinate φ representing an angle made between said curve and said reference line at said apex point
• computing for pixels of the image a quotient value representative of the aspect ratio of tissue structures depicted in the image;
• using a trained classifier to classify said pixels according to their respective said quotient values and assigning a score to the respective pixels representing their classification with respect to at least two classes;
• deriving said parameter that changes alongside changes in breast density based on the aggregate pixel membership scores of said classes.