An investigation into breast surface deformation and volume variation measurement

In the field of breast biomechanics, the majority of research has studied the motion of the breast throughout different movements using a single point marker for representation of this motion on the breast surface at the nipple. As a deformable mass however, there is a wealth of information lost by reducing the breast to a single point, so to support in the advancement of this research area this thesis explored the development of an effective means of capturing breast deformation.

The menstrual cycle is known to affect breast volume, resulting in an increase prior to the onset of menses followed by a decrease prior to ovulation. Volume of the breast across several menstrual cycles was investigated to determine if volume variation could be modelled, and whether variation would affect collection of breast deformation data. Mathematical equations fitted to the collected breast volume variation data demonstrated that modelling volume variation was possible as a sinusoidal function from known factors in longitudinal measurement of the breast volume, and produced a reliable prediction of cycle length. It was also demonstrated that longitudinal studies of breast deformation would not produce analogous results.

A unique data capture setup, using a multiple Digital Image Correlation system and a custom-built gimbal participant test rig, was used to measure deformation of the breast by increasing resolution of the torso surface to over 500x that of previous studies. By orienting the participant to the extremities of each anatomical plane under gravity, the area of the torso that deformed due to breast motion was identified. Using external measurements alone a breast motion-affected boundary was defined based on the displacement experienced by points across the torso surface.

With the torso surface that was affected by breast movement identified, a chest wall surface inferred from the remaining torso surface, and a representation of the breast volume was created. Comparison of displacement data collected from the nipple marker and that of a calculated centre of the breast volume found variation between the motion paths and subsequently estimated mechanical characteristics showed that the spring constant of the centre of volume was 2.8x larger than that of the nipple, indicating that the motion of the breast as measured at the nipple is not representative of gross breast motion, as previously assumed.