In mammographic breast compression, the importance of estimating and controlling pressure rather than force is understood to an increasing degree. Recent publications point out the benefits in terms of reproducibility, pain, radiation dose, image quality and even detectability of breast cancer. The average pressure applied by the paddle can be calculated as the applied force divided by the contact area between the breast and the paddle. In this study, we have assessed the accuracy of two methods of estimating the contact area.
METHOD AND MATERIALSFor a set of 300 breast compressions, we measured the contact areas between breast and paddle capacitively using a transparent indium-tin-oxide (ITO) foil attached to the paddle, and retrospectively from the obtained DICOM images using Volpara software (algorithm version 1.5.2). A gold standard was obtained from video images of the compressed breast captured from above using an optical camera. During each compression, the breast was illuminated from the sides in order to create a dark shadow on the video image where the breast was in contact with the compression paddle. We manually segmented the shadows captured at the time of X-ray exposure and measured their areas.
RESULTSWe found a strong correlation between the manual segmentations and the capacitive measurements (r² = 0.979) and between the manual segmentations and the Volpara measurements (r² = 0.955). The regression lines were both very close to the line of identity (respectively, y = 0.046 + 0.965x and y = 0.022 + 0.985x).
CONCLUSIONThe contact area between the paddle and the breast can be measured accurately, both in real-time using the capacitive method, and retrospectively using Volpara software. This finding substantiates many present and future studies that depend on one of these two methods for determining the pressure on the breast during mammographic compression.
CLINICAL RELEVANCE/APPLICATIONRecent evidence suggests that using too high pressure reduces the detectability of breast cancer. An accurate method to determine the contact area is essential to accurately estimate applied pressure.