What Is ALARA? The Radiation-Safety Principle Behind Every Scan
ALARA — 'As Low As Reasonably Achievable' — is the guiding principle that radiology uses to keep radiation dose as low as possible while still producing a diagnostic image.
Plain-language definition
ALARA stands for As Low As Reasonably Achievable. It's the guiding principle every diagnostic imaging center uses to keep radiation exposure as low as possible while still producing an image good enough to answer the clinical question.
Three pillars carry ALARA in practice:
- Time — the shorter the exposure, the lower the dose.
- Distance — radiation drops off rapidly with distance from the source (important for staff, less relevant for the patient being imaged).
- Shielding — lead aprons, thyroid shields, and built-in collimation reduce dose to body parts that aren't being imaged.
ALARA applies to anything that uses ionizing radiation: X-ray, CT, fluoroscopy, and nuclear medicine. It does not apply to MRI or ultrasound, neither of which uses ionizing radiation.
Why it matters
Every X-ray and CT scan carries a small radiation dose. Used appropriately, the benefit of an accurate diagnosis far outweighs the very small theoretical risk. But "appropriate use" is the entire point of ALARA — radiology should never use more dose than is needed.
For patients, ALARA shows up as:
- Right test, right time. A CT is not ordered when an ultrasound or MRI would safely answer the same question.
- Low-dose protocols. Modern CT scanners adjust the dose automatically based on patient size and body region. See our low-dose CT glossary entry.
- Shielding. Lead aprons or shields are used when they don't degrade image quality.
- Avoiding duplicate exams. If you've recently had imaging at another facility, share it with us — we'd rather review your prior study than repeat it.
ALARA is especially important for children, who are more sensitive to radiation, and for patients getting serial imaging (cancer follow-up, kidney-stone surveillance, etc.) where doses add up over time.
How ALARA shows up in a Precise Imaging context
Every CT, X-ray, and fluoroscopy room at Precise Imaging is run under an ALARA program:
- Our CT scanners use automated exposure control and iterative reconstruction so the dose is automatically reduced for smaller patients and smaller body regions.
- Pediatric and lung-cancer screening protocols are explicitly tuned to a low-dose recipe.
- Our technologists are credentialed and the equipment is calibrated to current standards.
- For X-rays, the field of view (collimation) is tightened to the body region of interest and shields are used when they would not interfere with the diagnostic question.
- A medical physicist reviews dose performance on a regular schedule.
If you have specific questions about the dose for a given exam, our technologists can show you the estimated dose-length product (DLP) for your CT or the dose-area product (DAP) for your fluoroscopy procedure.
Disclaimer
This page is general patient education. Decisions about whether a particular imaging test is appropriate for you are made by your ordering provider in consultation with the radiologist. If you are pregnant, may be pregnant, or have had a large amount of recent imaging, please tell our team before your appointment.
Frequently asked questions
Does ALARA mean zero radiation?
No. ALARA means as low as reasonably achievable while still getting a diagnostic-quality image. A dose so low that the image is non-diagnostic isn't useful — the scan would need to be repeated, doubling the total dose. ALARA balances dose against image quality.
How much radiation is in a CT scan?
It varies by exam and patient. A typical adult chest CT delivers about 5–7 mSv, similar to 2–3 years of natural background radiation. A low-dose lung screening CT can be as low as 1–2 mSv. See our millisievert explainer for context on dose units.
Should I refuse an X-ray or CT?
Not without talking to your provider. The risk of missing a serious diagnosis usually far exceeds the small theoretical radiation risk. ALARA is built into your exam to keep that risk as low as it can be.
Why doesn't ALARA apply to MRI?
MRI uses magnetic fields and radio waves, not ionizing radiation. There is no cumulative dose to track and no comparable cancer risk to manage. Ultrasound also uses no ionizing radiation.
Are kids treated differently?
Yes. Pediatric CT protocols use significantly lower doses than adult protocols, and children's smaller body size means automated dose modulation drops the technique even further. Precise uses pediatric-tuned recipes for every patient under roughly age 18.