A chest CT scan carries significantly more radiation than a mammogram. To put it simply, a typical chest CT scan delivers about 7 millisieverts (mSv) of radiation, whereas a standard mammogram exposes a person to roughly 0.4 mSv or less, depending on whether it is a 2D or 3D mammogram. This means a chest CT scan can expose you to roughly 15 to 20 times more radiation than a mammogram.
Radiation dose is measured in millisieverts, which quantifies the effect of ionizing radiation on the body. The higher the dose, the greater the potential risk, although medical imaging doses are generally kept as low as possible to balance diagnostic benefits with safety.
Mammograms use low-dose X-rays specifically targeted at breast tissue to detect early signs of breast cancer. The radiation dose from a mammogram is about the same as two months of natural background radiation that everyone is exposed to from the environment. Modern mammography equipment is designed to minimize radiation while producing high-quality images. Even with the addition of 3D tomosynthesis, which provides more detailed breast images, the radiation dose remains low and well within safety limits.
In contrast, a chest CT scan involves multiple X-ray images taken from different angles to create detailed cross-sectional views of the chest organs, including the lungs, heart, and blood vessels. Because it captures many images in a short time, the radiation dose is much higher than a single mammogram or chest X-ray. A chest X-ray, for comparison, delivers about 0.1 mSv, which is far less than a CT scan but still more than a mammogram.
The reason for the higher radiation dose in CT scans is the need for detailed, three-dimensional images that help diagnose or monitor conditions such as lung infections, tumors, or injuries. While the radiation dose is higher, the diagnostic value often outweighs the risk, especially when CT scans are used judiciously.
It is important to understand that the radiation from both mammograms and chest CT scans is relatively low compared to natural background radiation, which averages about 3 mSv per year from sources like soil, cosmic rays, and radon gas. However, the difference lies in how quickly the dose is delivered: medical imaging doses occur in seconds, whereas background radiation accumulates gradually over time.
Because radiation exposure carries a small risk of increasing cancer, medical professionals carefully weigh the benefits and risks before recommending imaging tests. Mammograms are recommended regularly for women over 40 because early detection of breast cancer significantly improves treatment outcomes and survival rates. The radiation risk from mammograms is considered negligible compared to the benefit of early cancer detection.
Chest CT scans are used when more detailed imaging is necessary, such as evaluating lung disease, trauma, or cancer spread. Although the radiation dose is higher, the information gained can be critical for diagnosis and treatment planning.
In summary, a chest CT scan exposes a person to much more radiation than a mammogram—about 7 mSv versus less than 0.5 mSv. Mammograms use low-dose X-rays focused on breast tissue and are safe for routine screening, while chest CT scans provide detailed images of the chest but with a higher radiation dose. Both tests have important roles in medical care, and their use is guided by balancing diagnostic benefits against radiation risks.