Knowledge awaits. See Subscription Options Already a subscriber? Create Account See Subscription Options. Continue reading with a Scientific American subscription. Subscribe Now You may cancel at any time. The amount the patient absorbs contributes to the patient's radiation dose. Radiation that passes through the body does not contribute to this dose. The scientific unit of measurement for whole body radiation dose, called "effective dose," is the millisievert mSv. Other radiation dose measurement units include rad, rem, roentgen, sievert, and gray.
Doctors use "effective dose" when they talk about the risk of radiation to the entire body. Risk refers to possible side effects, such as the chance of developing a cancer later in life.
Effective dose considers how sensitive different tissues are to radiation. If you have an x-ray exam that includes tissues or organs that are more sensitive to radiation, your effective dose will be higher. Effective dose allows your doctor to evaluate your risk and compare it to common, everyday sources of exposure, such as natural background radiation. We are exposed to natural sources of radiation all the time.
According to recent estimates, the average person in the U. These natural "background doses" vary according to where you live.
People living at high altitudes such as Colorado or New Mexico receive about 1. A coast-to-coast round-trip airline flight is about 0. The largest source of background radiation comes from radon gas in our homes about 2 mSv per year. Like other sources of background radiation, the amount of radon exposure varies widely depending on where you live. To put it simply, the amount of radiation from one adult chest x-ray 0. Here are some approximate comparisons of background radiation and effective radiation dose in adults for several radiology procedures described on this website.
Keep track of your x-ray history. It won't be completely accurate because different machines deliver different amounts of radiation, and because the dose you absorb depends on your size, your weight, and the part of the body targeted by the x-ray.
But you and your clinician will get a ballpark estimate of your exposure. Consider a lower-dose radiation test. If your clinician recommends a CT or nuclear medicine scan, ask if another technique would work, such as a lower-dose x-ray or a test that uses no radiation, such as ultrasound which uses high-frequency sound waves or MRI which relies on magnetic energy.
Consider less-frequent testing. If you're getting regular CT scans for a chronic condition, ask your clinician if it's possible to increase the time between scans.
And if you feel the CT scans aren't helping, discuss whether you might take a different approach, such as lower-dose imaging or observation without imaging. Don't seek out scans.
Don't ask for a CT scan just because you want to feel assured that you've had a "thorough checkup. And there's a chance the scan will find something incidental, spurring additional CT scans or x-rays that add to your radiation exposure. Measuring radiation If you mention the measurement of radiation, many people will recall the classic Geiger counter with its crescendo of clicks.
Average effective dose mSv. Range reported in the literature mSv. The main risks are those associated with.
The probability for absorbed x-rays to induce cancer or heritable mutations leading to genetically associated diseases in offspring is thought to be very small for radiation doses of the magnitude that are associated with CT procedures. Such estimates of cancer and genetically heritable risk from x-ray exposure have a broad range of statistical uncertainty, and there is some scientific controversy regarding the effects from very low doses and dose rates as discussed below.
To date, there is no evidence of genetically heritable risk in humans from exposure to x-rays. Under some rare circumstances of prolonged, high-dose exposure, x-rays can cause other adverse health effects, such as skin erythema reddening , skin tissue injury, and birth defects following in-utero exposure.
But at the exposure levels associated with most medical imaging procedures, including most CT procedures, these other adverse effects do not occur. Because of the rapidly growing use of pediatric CT and the potential for increased radiation exposure to children undergoing these scans, special considerations should be applied when using pediatric CT. Among children who have undergone CT scans, approximately one-third have had at least three scans.
The quantity most relevant for assessing the risk of cancer detriment from a CT procedure is the "effective dose". The unit of measurement for effective dose is millisieverts abbreviated mSv.
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