A non-contrast CT scan involves the use of ionizing radiation to create detailed images of the inside of the body without the injection of contrast dye. The amount of radiation contained in or delivered by a non-contrast CT scan varies depending on the body part being scanned, the specific CT machine settings, and patient factors such as size. Generally, the radiation dose is measured in millisieverts (mSv), which quantifies the potential biological effect of the radiation.
For a typical non-contrast CT scan, the radiation dose can range approximately as follows:
– **Head CT scan:** Around 2 mSv. This is relatively low because the head is smaller and requires less radiation to obtain clear images.
– **Chest CT scan:** Approximately 4 mSv for a non-contrast scan. This dose can increase if contrast is used.
– **Abdominal or pelvic CT scan:** Usually between 5 to 10 mSv for non-contrast scans, with doses increasing if contrast dye is administered.
To put these numbers in perspective, the average person is exposed to about 3 mSv of natural background radiation annually from environmental sources. So, a single non-contrast CT scan of the chest or abdomen can deliver a dose roughly equivalent to one to a few years of natural background radiation exposure.
The radiation dose in a non-contrast CT scan is carefully controlled and optimized to be as low as reasonably achievable while still providing diagnostic-quality images. For example, lung cancer screening CT scans are often performed as low-dose, non-contrast helical scans with radiation doses around or below 3 mGy (a related unit), which is considered low-dose for standard-sized patients.
Radiation exposure from CT scans carries a small but measurable risk of tissue damage and potential carcinogenesis over time. This risk is cumulative, meaning repeated scans increase the total radiation dose and thus the potential risk. Younger patients and radiosensitive organs are more vulnerable to radiation effects. However, the diagnostic benefits of CT scans often outweigh these risks, especially when scans are clinically justified.
In summary, a non-contrast CT scan typically delivers a radiation dose in the range of 2 to 10 mSv depending on the body region, which is controlled to minimize risk while providing critical diagnostic information. The radiation does not remain in the body after the scan; it is the exposure during the scan that matters. Medical professionals carefully consider the necessity of each scan and use protective measures to limit radiation exposure whenever possible.
