Mammography uses low-dose X-rays to examine the breast for screening and diagnosing diseases. This procedure relies on mechanical compression, applied to the breast tissue between two plates. Although often perceived as uncomfortable, compression is essential for obtaining a diagnostic image of sufficient quality to detect potential abnormalities.
The Essential Role of Compression
The primary purpose of compression is to transform the three-dimensional breast volume into a thinner, more uniform layer for imaging. This flattening is a physical necessity that directly affects the clarity and reliability of the resulting mammogram. By spreading the glandular tissue, compression helps separate overlapping structures that might otherwise hide a small mass or create a false appearance of an abnormality.
Compression also improves the technical aspects of image acquisition. It secures the breast in place, eliminating motion artifacts that cause blurring, even from involuntary movements like breathing. Reducing tissue thickness significantly decreases X-ray scatter, which improves image contrast and makes it easier to distinguish between healthy and diseased tissue. A thinner breast also requires a lower overall X-ray exposure, decreasing the radiation dose delivered to the patient.
Measuring the Applied Force
The mechanical force applied during a mammogram is measured in units of Newtons (N) or sometimes pounds of force. Modern mammography machines display this force in real-time for the technologist. The typical compression force applied ranges between 100 and 200 Newtons, which translates to approximately 22 to 45 pounds of force.
The goal of compression is to reduce the breast to a target thickness, not simply to reach a fixed force. The compressed breast tissue thickness is generally reduced to a range of 2 to 6 centimeters. While force is the standard measurement displayed, some researchers suggest that measuring pressure (force distributed over a given area) is a more standardized metric for evaluating compression effectiveness and comfort.
Factors Determining Final Compression
The specific force applied to a patient is determined by a dynamic balance of several variables. The primary factor is the patient’s subjective pain threshold and tolerance. Compression must cease immediately when the patient reports significant discomfort, even if the desired minimal thickness has not yet been achieved.
The physical composition of the breast tissue is another major determinant of the final compression level. Breasts with a higher proportion of dense, fibroglandular tissue require more force to flatten and spread out than those composed primarily of fatty tissue.
Additionally, all mammography equipment is designed with a regulatory safety limit, typically set at 200 Newtons, preventing the machine from exceeding a maximum force. This limitation ensures the procedure remains safe and prevents tissue injury. The final applied compression represents the maximum force that can be comfortably and safely tolerated while achieving an image of sufficient quality for accurate diagnosis.