Your doctor says you need imaging.

Then comes the alphabet soup.

X-ray.

CT.

MRI.

Ultrasound.

If an MRI produces incredibly detailed pictures, why wouldn’t everyone simply get an MRI?

If you already had an X-ray, why do you now need a CT scan?

And if your CT scan was normal, why might your doctor still order another kind of imaging?

It can feel as though one test should simply be “better” than another.

But that’s not really how medical imaging works.

Different imaging tests are designed to answer different questions.

The best test isn’t necessarily the biggest, newest, or most expensive machine.

It is the one most likely to provide the information your healthcare team needs.

X-Rays: Fast, Familiar and Very Useful

Most of us have had an X-ray at some point.

X-rays use a small amount of ionizing radiation to create images of structures inside the body.

They are particularly useful for looking at bones and are commonly used when healthcare professionals are evaluating fractures or certain joint and chest problems.

The test itself is usually quick.

You may be asked to stand, sit, or lie in a particular position while the images are taken.

An X-ray doesn’t show every type of tissue equally well, however.

So if an X-ray doesn’t answer the clinical question, your healthcare provider may need another kind of imaging.

That doesn’t make the X-ray a wasted test.

It answered what it was capable of answering.

CT Scans: Looking in Greater Detail

A CT scan—computed tomography—also uses X-rays, but instead of producing a single traditional image, the scanner collects information from multiple angles.

A computer then creates detailed cross-sectional images of the body.

Think of the difference this way:

A traditional X-ray is somewhat like looking at the outside of a loaf of bread.

A CT scan allows healthcare professionals to look at it in slices.

CT can provide detailed images quickly, which is one reason it is so useful in hospitals and emergency departments.

During the scan, you usually lie on a table that moves through a large ring-shaped scanner.

The examination itself is generally painless.

Depending on what your healthcare team is looking for, you may also receive contrast material.

What Is Contrast?

Contrast helps certain tissues, organs, or blood vessels appear more clearly on medical images.

It can be given in different ways depending on the examination.

Some contrast material is swallowed.

Some is given through an IV.

If contrast is planned, your healthcare team may ask about allergies, previous reactions, kidney problems, pregnancy, or other medical information depending on the type of study.

If you don’t understand why contrast is being used, ask.

A perfectly reasonable question is:

“What will the contrast help you see?”

MRI: Detailed Images Without X-Ray Radiation

MRI stands for magnetic resonance imaging.

Instead of X-rays, MRI uses a strong magnetic field, radio waves, and computer technology to produce detailed images.

MRI can be particularly useful for examining many types of soft tissue and structures such as the brain, spinal cord, joints, muscles, ligaments, and other areas of the body.

But MRI isn’t automatically the right test for every problem.

It usually takes longer than an X-ray or CT scan.

You need to remain relatively still.

The machine can be loud.

And because MRI uses a powerful magnet, certain implanted medical devices, metal fragments, or other materials may require special consideration before the examination.

You will usually be asked detailed safety questions before entering the MRI area.

Answer them carefully, even if something was implanted many years ago.

What If I’m Claustrophobic?

This is worth talking about before the day of the examination.

An MRI scanner can feel confined to some people.

If you know you are severely claustrophobic or have struggled with MRI examinations before, tell the healthcare professional ordering the test or the imaging department ahead of time.

There may be ways to make the experience easier depending on your circumstances and the type of examination needed.

You don’t get extra points for suffering silently through a test you’re terrified of.

Let someone know.

Ultrasound: Images Made With Sound Waves

Ultrasound works very differently.

It uses high-frequency sound waves to create images of structures inside the body.

There is no ionizing radiation.

A healthcare professional usually places gel on the skin and moves a handheld device called a transducer over the area being examined.

Ultrasound is commonly used to examine many organs and soft tissues and can also be used to evaluate blood flow.

Most people associate ultrasound with pregnancy, but its uses extend far beyond obstetrics.

Depending on the examination, you may receive preparation instructions such as fasting or arriving with a full bladder.

Those instructions aren’t arbitrary.

Sometimes the preparation helps the person performing the ultrasound obtain better images.

So Which Test Is Best?

There isn’t one.

That’s the point.

Imagine someone comes to a healthcare provider because of pain.

Depending on where the pain is, how it began, the person’s age, medical history, examination, and what the provider suspects, an X-ray might be appropriate.

For someone else, ultrasound might provide the most useful information.

Another person might need CT.

Another might need MRI.

And sometimes one test leads to another.

That isn’t necessarily because the first test failed.

The first examination may have answered one question and raised another.

Why Didn’t They Just Order the MRI First?

Patients understandably ask this.

MRI produces remarkably detailed images, so it can sound like the obvious place to start.

But detail isn’t the only consideration.

Healthcare professionals consider what structure they need to examine, what condition they are evaluating, how quickly information is needed, whether radiation or contrast is involved, the patient’s medical situation, and whether a particular test will actually answer the question.

Sometimes an X-ray is exactly the right test.

Sometimes CT is preferable.

Sometimes ultrasound provides the information needed without radiation.

Sometimes MRI provides detail another examination cannot.

More sophisticated does not always mean more appropriate.

What About Radiation?

X-rays and CT scans use ionizing radiation.

MRI and ultrasound do not.

That doesn’t mean you should automatically be afraid of X-rays or CT scans.

Medical imaging is ordered when the expected diagnostic benefit is considered important, and imaging professionals work to use radiation appropriately.

But it is reasonable to ask questions, particularly if you have undergone numerous imaging studies.

You can ask:

“Does this test use radiation?”

“Why is this the best imaging test for what we’re looking for?”

Those aren’t confrontational questions.

They’re informed ones.

Your Job Isn’t to Choose the Machine

The internet makes it tempting to walk into an appointment already convinced that you need an MRI, CT scan, or another specific test.

But choosing imaging is more complicated than matching a symptom to a machine.

You don’t need to know which scan to order.

You need to understand why the one being recommended is being ordered.

Ask:

“What are you looking for?”

“What will this test tell us?”

“Do I need to do anything to prepare?”

“Will I receive contrast?”

“When should I expect the results?”

And perhaps most importantly:

“What happens next if this doesn’t explain my symptoms?”

The Picture Is Still Only Part of the Story

Modern imaging allows healthcare professionals to see inside the human body with extraordinary detail.

But an image still needs interpretation.

Something seen on a scan may explain your symptoms.

Something else may simply be an incidental finding that has nothing to do with why you were tested.

And sometimes imaging looks reassuring even though symptoms continue and another part of the diagnostic process is needed.

An image is another piece of information.

It isn’t the whole patient.

So whether you are standing against an X-ray plate, moving through a CT scanner, listening to the thumping sounds of an MRI, or watching an ultrasound screen beside you, remember:

The machine isn’t trying to find everything that could possibly be wrong with you.

It is being used to help answer a particular question.

And you are always allowed to ask what that question is.

References

RadiologyInfo.org, American College of Radiology and Radiological Society of North America. X-ray (Radiography), Computed Tomography (CT), Magnetic Resonance Imaging (MRI), and General Ultrasound.

U.S. Food and Drug Administration (FDA). Medical X-Ray Imaging.

National Institute of Biomedical Imaging and Bioengineering (NIBIB). Magnetic Resonance Imaging (MRI).

National Institute of Biomedical Imaging and Bioengineering (NIBIB). Ultrasound.