Which scans use radiation — and which don't
CT (computed tomography), X-ray, mammography, and fluoroscopy use ionizing radiation (X-rays) to create their images. MRI and ultrasound use no ionizing radiation at all — MRI uses a magnetic field and radio waves, and ultrasound uses sound waves.
So if your exam is an MRI or ultrasound, radiation is not a consideration. If it is a CT or X-ray, the amount of radiation is small and chosen deliberately for your body size and the clinical question.
What "dose" actually means
Radiation dose is usually measured in millisieverts (mSv). It is a way of estimating how much energy your body absorbs and the very small associated risk. For context, everyone receives about 3 mSv per year just from natural background sources — the ground, the air, and outer space.
A single chest X-ray is about 0.1 mSv — roughly the natural background you would receive in about ten days. A CT scan ranges from about 1 to 10 mSv depending on the body region. These are small numbers, and the benefit of an accurate diagnosis almost always outweighs the very small theoretical risk.
Everyday comparisons
It can help to compare imaging radiation to things you already do. A transatlantic flight exposes you to about 0.05 mSv from cosmic radiation. Living for a year in a typical home adds a few mSv. A chest X-ray is about 0.1 mSv; a head CT about 2 mSv; a chest CT about 7 mSv; an abdomen/pelvis CT about 8–10 mSv.
In other words, a chest X-ray is roughly the background radiation of a week or two of ordinary life, and even a detailed CT is comparable to a couple of years of natural background exposure.
How we keep your exposure low (ALARA)
Radiology follows a principle called ALARA — As Low As Reasonably Achievable. It means using the smallest radiation dose that still answers the clinical question. At Precise Imaging that includes automatic exposure control on every scanner, modern reconstruction software that preserves image quality at lower dose, size-based pediatric protocols, and routine protocol review by a medical physicist.
Our radiologists also help avoid unnecessary radiation: if a requested scan looks duplicative, or if MRI or ultrasound could answer the same question without radiation, they will say so and discuss it with your provider.
Children, pregnancy, and special situations
Children are more sensitive to radiation, so every pediatric CT or X-ray uses a protocol sized to the child, delivering significantly less dose than the adult equivalent. We follow the Image Gently campaign on every pediatric study.
If you are or could be pregnant, tell us before any CT or X-ray. Radiation-using exams during pregnancy are generally avoided unless the information is essential, and we will look at whether MRI or ultrasound can answer the question instead.
If this applies to you
- If your exam is an MRI or ultrasound, you can set radiation worries aside — those tests use none.
- Ask your provider what specific question a CT or X-ray is meant to answer.
- Bring or request prior images on CD so a new scan can be compared instead of repeated.
- For children, confirm with our team that a pediatric (size-based) protocol will be used.
- Ask for a copy of your dose report after a CT — we are happy to provide it.
Call us before your appointment if…
- You are or could be pregnant and are scheduled for a CT or X-ray.
- You have had several CT scans of the same area recently and want to discuss cumulative dose.
- You are scheduling a CT or X-ray for a child and want to confirm pediatric protocols.
- You want to discuss whether MRI or ultrasound could answer the same question without radiation.
This page is general patient education and does not replace the medical advice of your physician. It describes how Precise Imaging operates today and is not a substitute for the specific instructions on your appointment confirmation. Always discuss your medical history with the provider who ordered your exam.
Frequently asked questions
Does an MRI or ultrasound use radiation?
No. MRI uses a magnetic field and radio waves, and ultrasound uses sound waves. Neither uses ionizing radiation, so radiation is not a concern for those exams.
How much radiation is in a typical imaging test?
A chest X-ray is about 0.1 mSv — roughly ten days of natural background radiation. A CT scan ranges from about 1 to 10 mSv depending on the body region. For comparison, everyone receives about 3 mSv per year from natural sources.
Is the radiation from a CT scan dangerous?
The dose from a single appropriate CT is small, and the benefit of an accurate diagnosis almost always outweighs the very small theoretical risk. We use dose-reduction technology and the lowest dose that still answers the clinical question. See our CT radiation dose guide for the specifics.
What is the ALARA principle?
ALARA stands for "As Low As Reasonably Achievable" — the commitment to use the smallest radiation dose that still produces a diagnostic-quality image. It guides every CT and X-ray we perform.
Should I worry about radiation building up from multiple scans?
If you have had several scans of the same area, it is reasonable to ask whether the next one is necessary or whether a different test could answer the question. We can share prior images with your provider so duplicate scans are avoided.
Is imaging radiation safe during pregnancy?
Exams that use radiation (CT, X-ray) are generally avoided during pregnancy unless the information is essential and cannot be obtained another way. MRI and ultrasound use no radiation and are often used instead. Always tell us if you are or could be pregnant.
Can children safely have a CT or X-ray?
Yes, when the test is clinically necessary. We use size-based pediatric protocols that deliver significantly less radiation than the adult-equivalent scan, following the Image Gently campaign.