Can an MRI show a broken bone?

Yes. MRI can show fractures that do not appear on X-ray, including bone bruises and stress fractures. The ACR recommends MRI without contrast when a knee X-ray is normal but a hidden fracture is still suspected. For an obvious fracture, an X-ray is usually all that is needed.

Is ultrasound as good as MRI for a rotator cuff tear?

The ACR rates both as usually appropriate after a normal or unclear shoulder X-ray when a rotator cuff problem is suspected. Ultrasound uses no ionizing radiation. MRI shows more of the joint, including cartilage and the labrum.

Why did my doctor order an X-ray before my MRI?

Most guidelines start with an X-ray because it is fast, cheap and rules out fractures, arthritis and calcium deposits. The ACR knee and shoulder criteria rate MRI as a next step after the X-ray, not as the first test. The X-ray result shapes which MRI, if any, is needed.

How long should I wait before getting an MRI for back pain?

Without red flags, Choosing Wisely recommendations from family physicians and spine surgeons advise no imaging in the first six weeks. Most back pain improves in less than 4 weeks. Red flags such as worsening leg weakness, a cancer history, trauma or suspected infection call for earlier imaging.

Does an X-ray or ultrasound use radiation?

An X-ray uses a small dose of ionizing radiation, which the ACR rates at less than 0.1 mSv for a knee or shoulder. Ultrasound and MRI use no ionizing radiation. That is one reason both are preferred in pregnancy.

When Is An X-Ray Or Ultrasound Enough, And When Do You Need An MRI?

The short answer: For most injuries and lumps, an X-ray or ultrasound comes first, and it is often enough. Guidelines move to MRI when the first test is normal or unclear but symptoms still point to a soft tissue problem, such as a torn ligament, rotator cuff tear or pinched nerve. For low back pain without warning signs, most people need no imaging at all in the first six weeks.

Why do doctors start with an X-ray or ultrasound?

Each test sees different things. X-rays show bone well: fractures, arthritis, alignment and calcium deposits. Ultrasound uses sound waves and shows tendons, fluid and lumps near the skin in real time. MRI shows the soft tissues in the most detail.

The National Institute of Biomedical Imaging and Bioengineering says MRI shows muscles, ligaments, tendons, nerves and the spinal cord much more clearly than X-ray or CT. That is why MRI is often used for knee and shoulder injuries. The same page notes that MRI is more expensive than X-ray or CT.

X-rays are fast, cheap and low dose. The American College of Radiology (ACR) rates a knee or shoulder X-ray at less than 0.1 mSv of radiation. Ultrasound and MRI use no ionizing radiation at all. Ultrasound has limits, though. RadiologyInfo explains that air, gas and bone block sound waves, and larger patients are harder to image.

So the usual logic is simple. Start with the cheap, fast test that can answer the question. Move to MRI when that test cannot. If you are weighing MRI against CT instead, see our MRI vs CT guide.

When is an X-ray enough for a knee or ankle injury?

Many knee and ankle injuries need no imaging at all. Doctors use short checklists called the Ottawa rules to decide. The ACR Acute Trauma to the Knee criteria list the Ottawa Knee Rule. Adults 18 and older need a knee X-ray if any of these apply:

Age 55 or older
Tenderness over the head of the fibula (the bony bump on the outer knee)
Tenderness over the kneecap only
Cannot bend the knee to 90 degrees
Could not bear weight right after the injury, and cannot take 4 steps in the emergency room

The ACR document cites a review of 1,967 knee injuries. About 74.1% of patients had X-rays, and only 5.2% of those showed a fracture. For the ankle, a BMJ systematic review of the Ottawa ankle rules found a sensitivity of almost 100%. The authors said using the rules should cut unnecessary X-rays by 30 to 40%.

After a twisting knee injury, the ACR rates MRI as "usually not appropriate" as the first test. X-ray comes first. If the X-ray shows no fracture but the doctor suspects a hidden fracture or a torn ligament or meniscus, MRI without contrast becomes "usually appropriate." Our knee MRI guide covers what that scan shows.

What about shoulder pain?

For long-lasting shoulder pain, the ACR Chronic Shoulder Pain criteria rate an X-ray as "usually appropriate" for the first test. Ultrasound is only "may be appropriate" at that stage. The X-ray rules out arthritis, bone problems and calcium in the tendons.

The next step depends on what the doctor suspects. For a possible rotator cuff tear or bursitis with a normal or unclear X-ray, the ACR rates three tests as "usually appropriate":

MRI without contrast
Ultrasound
MR arthrography (MRI after dye is injected into the joint)

This is a case where ultrasound can stand in for MRI. The ACR gives ultrasound and MRI the same "usually appropriate" rating for a suspected rotator cuff problem. Ultrasound uses no radiation and no magnet. MRI can also show other shoulder structures the ACR lists as pain sources, such as the labrum, cartilage and bone.

Do you need an MRI for low back pain?

Usually not, at least not early. The American College of Physicians and American Pain Society guideline says clinicians should not routinely order imaging for nonspecific low back pain. Imaging is advised when there are severe or progressive nerve problems, or when a serious cause is suspected.

The guideline also sets a narrow role for MRI in sciatica or spinal stenosis. MRI (preferred) or CT is advised for persistent symptoms only if the patient may be a candidate for surgery or an epidural steroid injection.

Several Choosing Wisely recommendations say the same thing. The American Academy of Family Physicians advises no imaging in the first six weeks unless red flags are present. The North American Spine Society advises no MRI in that window without red flags. Red flags named there include:

Severe or worsening nerve deficits, such as leg weakness
A history of cancer
Trauma or a suspected fracture
Suspected infection

The ACR low back pain summary notes most people get better in less than 4 weeks. For suspected cauda equina syndrome, where nerves in the lower back are severely compressed, MRI is "usually appropriate." After trauma, or in older adults, people with osteoporosis or steroid users, X-ray, MRI and CT are all rated "usually appropriate."

When does a lump need an MRI?

For a lump near the skin, the ACR Soft-Tissue Masses criteria rate X-ray or ultrasound as "usually appropriate" first tests. For deeper lumps, or lumps in areas that are hard to examine, X-ray is usually appropriate first, and ultrasound may be.

If those tests cannot identify the lump, MRI with and without IV contrast, or MRI without contrast, is "usually appropriate." The ACR says imaging of a lump that cannot be confirmed as harmless on exam guides diagnosis, staging and biopsy planning. Most soft tissue lumps are harmless, but some are cancer.

If you are still trying to work out what a new symptom means before any test, symptom.md has plain-language symptom guides.

What if you are pregnant or have belly pain?

Pregnancy is where ultrasound and MRI work as a team. The American College of Obstetricians and Gynecologists says ultrasound and MRI are "the imaging techniques of choice for the pregnant patient." ACOG adds that gadolinium contrast should be limited in pregnancy. It should be used only if it clearly improves the diagnosis and the outcome.

For pelvic pain that is likely gynecologic in a pregnant patient, the ACR rates ultrasound as "usually appropriate" and MRI and CT as "usually not appropriate," per the RadiologyInfo summary. For suspected appendicitis in a pregnant patient with fever and a high white cell count, the ACR rates both abdominal ultrasound and MRI without contrast as "usually appropriate" (right lower quadrant pain criteria).

MRI adds value when bowel gas blocks the ultrasound view, since air and gas disrupt sound waves. More on safety is in our guide to MRI while pregnant.

The bottom line

An X-ray or ultrasound is enough when it answers the question: a clear fracture, a simple cyst, arthritis or a fluid collection. MRI earns its place when the first test is normal or unclear and symptoms still suggest a soft tissue injury, a nerve problem or an unexplained mass. For back pain without red flags, waiting six weeks is the guideline default. If your doctor skips straight to MRI, or refuses one, ask which result would change your treatment.

Last updated: September 2026. This article is for informational purposes only and does not constitute medical advice. Talk with your doctor about which imaging test fits your symptoms and history.