Ask anyone who has had a mammogram what they remember most, and the answer is almost always the same: the compression. That firm, deliberate press of the paddle is one of the most talked-about aspects of the entire experience — and one of the most misunderstood.
For many people, compression feels like something being done to them. In reality, it is something done for the image — and ultimately, for their benefit. Understanding why compression happens, and what it achieves, can transform an uncomfortable moment into a meaningful one.
Compression is not incidental to the mammogram. It is foundational to it. Without adequate compression, the very quality that makes mammography effective is dramatically reduced.
This article breaks down the mechanics, the clinical benefits, and the evidence behind compression in mammography — and what patients can do to make the experience more comfortable without compromising image quality.
What actually happens during compression?
When a mammogram is taken, the breast is placed on the detector plate and a compression paddle is lowered, applying firm, controlled pressure. The force typically ranges from around 80 to 200 Newtons — roughly equivalent to 8 to 20 kilograms resting on the breast.
Typically, modern mammography units apply compression manually, i.e. controlled by the Radiographer. The compression is held for only a few seconds — typically the fraction of a second required for image acquisition — then released immediately.
To understand why this matters, it helps to think about what the X-ray system is trying to do: distinguish subtle differences between different types of breast tissue — fat, glandular tissue, fibrous connective tissue, and potentially abnormal tissue — using differences in how each absorbs X-ray energy. Anything that blurs, obscures, or distorts that picture works against accurate diagnosis.
Four ways compression improves your mammogram
1. It reduces tissue thickness
The most direct effect of compression is physical: it flattens the breast, reducing the depth of tissue the X-ray beam must pass through.
This matters for two reasons:
First, thinner tissue requires less radiation to penetrate fully, reducing dose.
Second, it physically separates overlapping structures — particularly dense glandular tissue — that might otherwise stack on top of each other and obscure a lesion beneath them.
2. It immobilises the breast
Even very slight movement during image acquisition — measured in fractions of a second — can produce motion blur. In mammography, where the diagnostic task includes identifying pathologies that may be under a millimetre in size, motion blur can render an otherwise adequate image non-diagnostic. Firm compression holds the breast securely against the detector, eliminating movement as a variable.
3. It lowers radiation dose
Modern mammography units use automatic exposure control (AEC) — a system that adjusts the X-ray output based on the measured thickness and density of the tissue being imaged. With less tissue to penetrate, the AEC selects a lower dose setting, which directly reduces mean glandular dose (MGD), the primary dose metric in breast imaging. Adequate compression is therefore not only about image quality; it is also a dose-reduction tool. Overall, this makes this test safer.
4. It brings tissue closer to the detector
Here we get a bit technical. Geometric unsharpness — the blurring caused by distance between a structure and the image receptor — increases the further tissue sits from the detector surface. In an uncompressed breast, posterior structures may be several centimetres from the receptor. Compression reduces this distance across the entire breast volume, improving the sharpness of deep structures and making their margins clearer on the image.
What about radiation dose?
Concerns about radiation are understandable and worth addressing directly. The mean glandular dose from a standard two-view mammogram of both breasts is approximately 0.4 milligrays (mGy) — an extremely low exposure by any clinical standard.
| Imaging Procedure | Approximate Dose |
|---|---|
| 2-view mammogram (both breasts) | ~0.4 mGy |
| Chest X-ray | ~0.1 mGy |
| Abdominal CT scan | ~10 mGy |
| Chest CT scan | ~7 mGy |
| Daily background radiation (approx) | ~0.01 mGy |
Dose figures are approximate and provided for contextual comparison only. Values vary by patient, equipment, and protocol. Sources: ARPANSA, ACR, IAEA.
Adequate compression directly contributes to keeping this dose low. A poorly compressed breast requires more X-ray energy to penetrate adequately and may require a repeat acquisition — doubling the dose for that view. In this way, good compression is good radiation safety practice.
Why does it hurt for some more than others?
Pain, or discomfort, perception during mammographic compression varies considerably between individuals and is influenced by a range of factors: breast density and composition, hormonal status, and contributing factors such as prior breast surgery, and individual pain tolerance. People with denser, more glandular tissue may experience more sensitivity than those with predominantly fatty breasts.
It is worth noting that discomfort does not mean harm. There is no clinical evidence that compression at mammographic forces causes tissue damage or injury in people without specific contraindications. People with breast implants, or those who have recently had breast surgery, should always inform their radiographer so that modified techniques can be applied.
Is compression changing with new technology?
Mammography technology continues to evolve, and compression is an active area of research and innovation. Pressure-based compression — which measures the pressure distribution across the entire breast surface rather than applying a fixed total force — is increasingly used in modern equipment and produces more uniform, comfortable compression tailored to individual tissue stiffness.
Digital breast tomosynthesis (DBT), now used widely as both a screening and diagnostic tool, benefits from compression in precisely the same ways as conventional 2D mammography. The physics of scatter reduction, geometric unsharpness, and tissue immobilisation apply equally.
Intelligent compression devices — which measure tissue resistance in real time and adjust force accordingly — represent the next stage of development, aiming to achieve optimal image quality at the lowest compression force that achieves it, personalised to everyone.
Optimal compression, clearer insights
Compression in mammography is not a design flaw or an unfortunate necessity. It is a core diagnostic tool — one that directly improves image contrast, reduces radiation dose, prevents motion blur, and helps ensure that small or subtle lesions are not hidden beneath overlapping tissue.
We at the Canberra Breast Clinic understand that discomfort is real, and it should be taken seriously. Radiographers are trained to balance image quality requirements with patient experience, and good communication before and during the examination makes a meaningful difference. But understanding why compression is applied — and what is at stake if it is not — gives patients the context to approach their screening with confidence rather than apprehension.
References
- Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). (2017). Radiation protection in mammography. ARPANSA Radiation Protection Series. Australian Government.
- American College of Radiology (ACR). (2018). ACR practice parameter for the performance of screening and diagnostic mammography. ACR.
- BreastScreen Australia. (2020). BreastScreen Australia national accreditation standards. Australian Institute of Health and Welfare. Australian Government.
- Chida, K., et al. (2009). Reduced compression mammography to reduce breast pain. Clinical Imaging, 33(1), 7–10.
- Helvie, M. A. (2010). Digital mammography imaging: breast tomosynthesis and advanced applications. Radiologic Clinics of North America, 48(5), 917–929.
- International Atomic Energy Agency (IAEA). (2011). Radiation protection in newer medical imaging techniques: PET/CT. Safety Reports Series No. 58. IAEA.
- Kornguth, P. J., et al. (1993). Impact of patient-controlled compression on the mammography experience. Radiology, 186(1), 99–102.
- Poulos, A., & McLean, D. (2004). The application of breast compression in mammography: a new perspective. The Breast, 13(6), 477–480.
- Rutter, D. R., et al. (1992). Discomfort and pain during mammography: description, prediction, and prevention. BMJ, 305(6851), 443–445.
- Whelehan, P., et al. (2013). The effect of mammography pain on repeat participation in breast cancer screening: a systematic review. The Breast, 22(4), 389–394.