Share this page:

Imaging Tests Explained

Read below to learn more about these diagnostic tests and why they may be recommended for you.

CT or CAT scan – Computed Tomography
A computed tomography (CT) scan uses X-rays to make detailed pictures of structures inside of the body. Doctors use CT scans to look for broken bones, cancers, blood clots, signs of heart disease, and internal bleeding.

During a CT scan, you lie still on a table. The table slowly passes through the center of a large X-ray machine. The test is painless. During some tests you receive a contrast dye, which makes parts of your body show up better in the image.

MRI – Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) uses a large magnet and radio waves to look at organs and structures inside your body. MRI can be used to look for problems such as bleeding, tumors, infection, blockage, or injury in the brain, organs and glands, blood vessels, and joints.

During the scan, you lie on a table that slides inside a tunnel-shaped machine. Doing the scan can take a long time, and you must stay still. The scan is painless.

PET scan – Positron Emission Tomography
Positron Emission Tomography is a specialized radiology procedure that uses radioactive substances to see structures and functions inside your body. They use a special camera that detects radioactivity. Nuclear scans can help doctors diagnose many conditions, including cancers, injuries, and infections. They can also show how organs like your heart and lungs are working.

Before the test, you receive a small amount of radioactive material. You may get it as an injection. Sometimes you swallow it or inhale it. Then you lie still on a table while the camera makes images.

Ultrasound
Ultrasound is a type of imaging. It uses high-frequency sound waves to look at organs and structures inside the body. Health care professionals use it to view the heart, blood vessels, kidneys, liver, and other organs. During pregnancy, doctors use ultrasound to view the fetus. Unlike x-rays, ultrasound does not expose you to radiation.

During an ultrasound test, you lie on a table. A special technician or doctor moves a device called a transducer over part of your body. The transducer sends out sound waves, which bounce off the tissues inside your body. The transducer also captures the waves that bounce back. The ultrasound machine creates images from the sound waves.

X-ray
X-rays are a type of radiation called electromagnetic waves. X-ray imaging creates pictures of the inside of your body. The images show the parts of your body in different shades of black and white. This is because different tissues absorb different amounts of radiation. Calcium in bones absorbs x-rays the most, so bones look white. Fat and other soft tissues absorb less, and look gray. Air absorbs the least, so lungs look black. The most familiar use of x-rays is checking for broken bones, but x-rays are also used in other ways. For example, chest x-rays can spot pneumonia. Mammograms use x-rays to look for breast cancer.

When you have an x-ray, you may wear a lead apron to protect certain parts of your body. The amount of radiation you get from an x-ray is small. For example, a chest x-ray gives out a radiation dose similar to the amount of radiation you're naturally exposed to from the environment over 10 days.

For more information, read answers to frequently asked questions about radiology at El Camino Hospital.

This article first appeared in the March 2016 edition of the HealthPerks newsletter.

You may also be interested in...

Visitor Screener

Visitor Restrictions

A visitor policy is in effect due to more restrictive measures being taken throughout the Bay Area.
HealthPerks Banner

Sign Up for HealthPerks

Get health information, event invitations, free screenings and more delivered to your inbox.
Find a doctor who will fit you well.

Find a Doctor

Use our directory to find a doctor with an office near our Mountain View or Los Gatos campus.