During mammographic acquisition, the breast is compressed between the breast support plate and the compression paddle to improve image quality and reduce dose, among other reasons. The applied force, which is measured by the imaging device, varies substantially, due to local guidelines, positioning, and breast size. Force measurements may not be very relevant though, because the amount of compression will be related to pressure rather than force. With modern image analysis techniques, the contact surface of the breast under compression can be determined and pressure can be computed retrospectively. In this study, we investigate if there is a relation between pressure applied to the breast during compression and screening performance.
In a series of 113,464 screening exams from the Dutch breast cancer screening program we computed the compression pressure applied in the MLO projections of the right and left breasts. The exams were binned into five groups of increasing applied pressure, in such a way that each group contains 20% of the exams. Thresholds were 7.68, 9.18, 10.71 and 12.81 kPa. Screening performance measures were determined for each group. Differences across the groups were investigated with a Pearson's Chi Square test. It was found that PPV and the cancer detection rate vary significantly within the five groups (p = 0.001 and p = 0.011 respectively).The PPV was 25.4, 31.2, 32.7, 25.8 and 22.0 for the five groups with increasing pressure. The recall rate, false positive rate and specificity were not statistically significant from the expectation (p-values: 0.858, 0.088 and 0.094 respectively). Even though differences are not significant, there is a trend that the groups with a moderate pressure have a better performance compared to the first and last category.
The results suggest that high pressure reduces detectability of breast cancer. The best screening results were found in the groups with a moderate pressure.