Under pressure: Lack of consistency results in varying mammographic compression

Breast compression, while uncomfortable for some women, is a necessary component of mammography. A recent international study has shown that, because of a lack of consistent guidelines, a wide variation exists in the technical execution of scans and the compression forces used.

Study authors Woutjan Branderhorst, PhD, of the Department of Biomedical Engineering and Physics at the Academic Medical Center in Amsterdam, and colleagues suggested standardization that measures pressure rather than force could improve patient care.

“Variation in applied compression that is caused by differences in the methods employed by radiographers is not desirable, because it suggests unwanted variation in standard of care, and undermines the consistency and reproducibility of the imaging procedure,” wrote the authors. “This leads to unpredictable differences in image [signal difference-to-noise ratio], radiation dose, and patient experience, between and within women.”

On current mammography systems, the only mechanical parameters to estimate the degree of breast compression from a compression paddle is force measured in dekanewtons (daN). The appropriate amount of force to use is subjective, however, and individual differences in breast size and elasticity vary the amount of force required. Pressure, measured in kilopascals (kPa), is force divided by the contact area and has the advantage of being independent of breast size and elasticity.

Branderhorst and colleagues sought to compare compression practice between imaging sites in the Netherlands and the U.S. They retrospectively evaluated the parameters of 37,518 mammographic compressions (for 9,188 women) from the Dutch national breast cancer screening program and a set of 7,171 compressions (for 1,851 women) from a Pittsburgh-based breast imaging center. Results were published in the April edition of the European Journal of Radiology.

Using software (VolparaAnalytics) that could retroactively estimate the contact area and thus the average pressure, the authors found large variations between and within imaging sites, with forces and pressures applied in the Netherlands data set significantly higher than the U.S. data set. Compressions with a force of >15 daN occurred in 31.1 percent of Dutch scans versus 1.5 percent in the U.S. Pressures of greater than 20 kPa were present in 12.3 percent and 1.7 percent of Dutch and U.S. scans, respectively.

The relative standard deviation of forces and pressures was larger in the U.S. data set. Average glandular radiation dose was also higher in the U.S. data set.

The authors noted that increased standardization based on pressure would make the procedure and images more reproducible, limit patient pain and reduce radiation dose related to insufficient compression.

“[Standardization based on pressure] inherently results in an objective and therefore more consistent adjustment to the combination of breast size and elasticity (by contact area). Because the size of the contact area changes during the compression, the adjustment of the compression would preferably be guided by a real-time indicator,” wrote Branderhorst and colleagues.