- What are imaging tests?
- Who does imaging tests and who interprets them?
- Types of imaging tests
- Computed tomography (CT) scan
- Magnetic resonance imaging (MRI)
- X-rays and other radiographic tests
- Nuclear medicine scans
- Categories of some common imaging tests
- Questions about radiation risk from imaging tests
- Factors that determine which imaging tests are used in different types of cancer
- To learn more
Other names include ultrasonography, sonography, or sonogram.
What does it show?
An ultrasound machine creates images called sonograms by giving off high-frequency sound waves that go through your body. As the sound waves bounce off your organs and tissues, they create echoes. The machine makes these echoes into real-time pictures that can be seen on a computer screen.
Ultrasound is very good at getting pictures of some soft tissue diseases that do not show up well on x-rays. Ultrasound is also a good way to tell fluid-filled cysts from solid tumors because they make very different echo patterns. It is useful in some situations because it can usually be done quickly and does not expose people to radiation.
Ultrasound images are not as detailed as those from CT or MRI scans. Ultrasound cannot tell a benign (not cancer) tumor from one that is cancer. Its use is also limited in some parts of the body because the sound waves cannot go through air (such as in the lungs) or through bone.
Doctors often use ultrasound to guide a needle to do a biopsy (taking out fluid or small tissue samples to be looked at under a microscope). The doctor looks at the ultrasound screen while moving the needle and can see the needle moving toward and into the tumor.
For some types of ultrasound exams, the transducer (the wand that produces the sound waves and detects echoes) is rubbed over the skin surface. The sound waves pass through the skin and reach the organs underneath. In other cases, to get the best images, the doctor must use a transducer that’s put into a body opening, such as the esophagus (the tube connecting the throat and the stomach), rectum, or vagina.
Special ultrasound machines, known as Doppler flow machines, can show how blood flows through vessels. This is helpful because blood flow in tumors is different from that in normal tissue. Some of these machines make color pictures. Unlike other forms of blood vessel imaging, color Doppler studies do not use contrast agents. Color Doppler has made it easier for doctors to find out if cancer has spread into blood vessels, especially in the liver and pancreas.
How does it work?
An ultrasound machine has 3 key parts: a control panel, a display screen, and a transducer, which usually looks a lot like a microphone or a computer mouse. The transducer sends out sound waves and picks up the echoes. The doctor or ultrasound technologist moves the transducer over the part of the body being studied. The computer inside the main part of the machine analyzes the signals and puts an image on the display screen.
The shape and intensity of the echoes depend on how dense the tissue is. For example, most of the sound waves pass right through a fluid-filled cyst and send back very few or faint echoes, which makes them look black on the display screen. But the waves will bounce off a solid tumor, creating a pattern of echoes that the computer will show as a lighter-colored image.
How do I get ready for the test?
For most ultrasounds, no preparation is needed, but it depends on what’s being studied. Your doctor or nurse will give you instructions about any steps to take before your test. Depending on the organ being studied, you may need to not eat, take a laxative, or use an enema. If you are having an abdominal (belly) ultrasound, you might need to drink a lot of water just before the study to fill your bladder. This will create a better picture because sound waves travel well through fluid.
What is it like having the test?
Ultrasound can be done in a doctor’s office, clinic, or hospital. Most often you will lie down on a table. The technologist will put a gel on your skin and move the transducer over the area. The gel both lubricates the skin and helps conduct the sound waves. The gel feels cool and slippery. If a probe is used, it will be covered with gel and put into the body opening. This can cause pressure or discomfort.
During the test the technologist or the doctor moves the transducer as it is firmly pressed to your skin. You may be asked to hold your breath during the scan. The operator may adjust knobs or dials to increase the depth to which the sound waves are sent. You may feel slight pressure from the transducer.
How long does it take?
An ultrasound usually takes 20 to 30 minutes. The length of time depends on the type of exam and how hard it is to find any changes in the organs being studied.
What are the possible complications?
Ultrasound is a very safe procedure with a low risk of complications.
What else should I know about this test?
- Ultrasound does not use radiation.
- Ultrasound usually costs much less than CT or MRI.
- The quality of the results depends to a large extent on the skill of the technologist or doctor operating the transducer, which is not the case with CT or MRI.
- Good images are harder to get in people who are obese.
- Newer forms of ultrasound can provide 3-D images.
Last Medical Review: 03/16/2015
Last Revised: 03/16/2015