A CT scan exposes the body to significantly more radiation than a standard diagnostic X-ray. While both use ionizing radiation to create images of the inside of the body, the amount of radiation delivered during a CT scan is generally much higher because it takes multiple X-ray images from different angles to produce detailed cross-sectional views. For example, a typical chest X-ray exposes a person to about 0.1 millisieverts (mSv) of radiation, which is roughly equivalent to 10 days of natural background radiation. In contrast, a chest CT scan can expose a person to around 4 to 6 mSv, and abdominal or pelvic CT scans can deliver up to 16 mSv or more, depending on whether contrast dye is used.
The reason CT scans involve more radiation is that they provide much more detailed and comprehensive images than a single X-ray. A standard X-ray produces a flat, two-dimensional image, which is often sufficient for diagnosing fractures or certain infections. CT scans, however, combine many X-ray images taken from multiple angles using a rotating scanner and computer processing to create detailed three-dimensional images of bones, organs, blood vessels, and soft tissues. This level of detail is crucial for diagnosing complex conditions such as tumors, internal bleeding, strokes, or infections that might not be visible on a plain X-ray.
Because of the higher radiation dose, CT scans carry a slightly increased risk of long-term effects, such as a small increase in lifetime cancer risk, especially if multiple scans are performed over time. This risk is generally low but is more significant for children, who are more sensitive to radiation. Medical professionals follow the ALARA principle—keeping radiation “As Low As Reasonably Achievable”—to minimize exposure by using the lowest effective dose and only ordering CT scans when the benefits outweigh the risks.
In contrast, diagnostic X-rays use much lower doses of radiation and are considered very safe for routine use. They are often the first imaging test ordered because they provide quick, useful information with minimal radiation exposure. However, they are less detailed and may not detect certain conditions that require the more advanced imaging capabilities of a CT scan.
Modern CT technology has improved to reduce radiation doses compared to older machines, but CT scans still deliver significantly more radiation than standard X-rays. Alternatives like MRI or ultrasound, which do not use ionizing radiation, may be preferred in some cases, especially for repeated imaging or for vulnerable populations such as pregnant women.
In summary, CT scans involve higher radiation exposure than diagnostic X-rays because they produce more detailed images by combining multiple X-ray images. This increased radiation dose means CT scans carry a slightly higher risk, but they are invaluable for diagnosing complex medical conditions that cannot be adequately assessed with standard X-rays. Medical professionals carefully weigh the risks and benefits before recommending either imaging method.