A stiff compression device which is parallel to the film surface should be utilised. Posterior sloping of the compression device at the base of the breast is undesirable because relative under-penetration of the base of the breast may occur. The posterior surface should be absolutely straight and should align precisely with the back of the film. The sharp posterior angle allows the compression device to grip the posterior aspect of the breast tissue during operation. This enables improved visualisation of the posterior aspect of the breast.
Vigorous compression is essential for screen-film mammography.
The average breast can usually be compressed to about 4cm in thickness. The value of compression should be carefully explained to the patient, and her co-operation requested. The increased subject contrast improves detection of calcification and visualisation of the outline of masses. Even arterial motion should be suppressed. With inadequate compression, considerable motion unsharpness can occur even with exposure times of only 0.2 second.