- 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
X-rays and other radiographic tests
Other names include radiographs, roentgenograms, and contrast studies. For names of contrast studies, see Table 1.
What do they show?
Radiographs, most often called x-rays, produce shadow-like images of bones and certain organs and tissues. X-rays are very good at finding bone problems. They can show some organs and soft tissues, but MRI and CT scans often give better pictures of them. Still, x-rays are faster, easy to get, and cost less than other scans, so they may be used to get information quickly.
Mammograms (breast x-rays) are a form of radiographic study (for more information, see the section “Mammography”).
Special types of x-ray tests called contrast studies use dyes or contrast materials along with the x-rays to create better pictures. For example, a lower gastrointestinal (GI) series, often called a barium enema exam, takes x-ray pictures after the bowel is filled with barium sulfate (a contrast material). Another contrast study, an intravenous pyelogram (IVP), uses dye to look at the structure and function of the urinary system (ureters, bladder, and kidneys). See Table 1 for more examples.
How do they work?
A special tube inside the x-ray machine sends out a controlled beam of radiation. Tissues in the body absorb or block the radiation to varying degrees. Dense tissues such as bones block most radiation, but soft tissues, such as fat or muscle, block less. After passing through the body, the beam falls on a piece of film or a special detector. Tissues that block high amounts of radiation, such as bone, show up as white areas on a black background. Soft tissues block less radiation and show up in shades of gray, and organs that are mostly air (such as the lungs) normally look black. Tumors are usually denser than the tissue around them, so they often show up as lighter shades of gray.
Contrast studies provide some information that standard x-rays cannot. During a contrast study, you get a dose of a contrast material that outlines, highlights, or fills in parts of the body so that they show up more clearly on an x-ray. The contrast material may be given by mouth, as an enema, as an injection (put in a vein), or through a catheter (thin tube) put into various tissues of the body. For most of these tests, the images can be captured either on x-ray film or by a computer.
Table 1: Commonly used contrast studies
Dye is given by
Angiography, angiogram, arteriography, arteriogram
Arteries throughout the body, including those in the brain, lungs, and kidneys
Catheter (thin tube) in an artery
Intravenous pyelogram (IVP)
Urinary tract (kidney, ureters, bladder)
Injection into vein (IV)
Lower GI (gastrointestinal) series, barium enema (BE), double-contrast barium enema (DCBE), air-contrast barium enema (ACBE)
Upper GI series, barium swallow, esophagography, small bowel follow through
Esophagus, stomach, small intestine
Veins throughout the body, most often in the leg
Catheter in a vein
How do I get ready for the test(s)?
Other than removing metal objects that might interfere with the picture, no special preparation is needed before having a standard x-ray.
Preparation for a contrast study depends on the test. You may be asked not to eat anything or to prepare in other ways before the test (see the next section). The radiology center where you are having the test will give you instructions. Check with them first. Your doctor also might give you instructions.
What is it like having the test(s)?
Standard x-rays: Usually x-rays are taken by an x-ray technologist. You will undress to expose the part of the body that will be x-rayed, removing jewelry or other objects that might interfere with the image. You may be given a gown or drape to wear. You will be asked to sit, stand, or lie down, depending on what part of the body will be x-rayed. Your body is put against a flat box that holds the x-ray film. The technologist then moves the machine to aim the beam of radiation at the right area.
You may have special shields put over parts of your body near the area being x-rayed so that they are not exposed to the radiation. Usually the technologist leaves the room to operate the machine by remote control. Your exposure to the x-ray is very brief—usually less than a second. You may hear a buzzing or clicking sound while the machine is working.
For a chest x-ray, often 2 views are taken. First, you stand with your chest against the x-ray film and the image is taken from the back. Your arms will be at your side. Then often a side view is taken with your arms either above your head or in front of you. The technologist will tell you when to take a deep breath and hold still. For a chest x-ray in people who can’t stand, the film is placed in back of them (under them) and the picture is taken from the front.
During an abdominal (belly) x-ray, you lie down on a table. You may be asked to change position or sit up if more than one view is needed. Again, you will need to hold your breath and lie still while the picture is taken quickly. After the exposure, the technologist will come back to the room to move the machine out of the way, remove any protective shields, collect the film, and help you back to the changing room where you can get dressed.
X-ray angiography: In the past, angiography was often used to help learn the stage or extent of cancer, but now CT and MRI scans are most often used to do this. Angiography is sometimes used to show surgeons the blood vessels next to a cancer so the operation can be planned to limit blood loss. Angiograms are still used to diagnose non-cancerous blood vessel diseases. These types of studies are done by a radiologist (a doctor who specializes in imaging), with the help of technologists.
You will be asked to not eat before this test. Usually you will be given medicine to relax you before the test starts. As you lie still on the table, the skin over the injection site is cleaned and numbed. A catheter (thin plastic tube) is put into a blood vessel (usually the artery at the top of the thigh) and slid in until it reaches the area to be studied. The contrast dye is put in, and a series of x-ray pictures is taken. After that, the catheter is removed. Firm pressure might be needed on the catheter site for a while to make sure it doesn’t bleed. You will also be asked to lie flat and keep your leg still for up to several hours. This helps prevent bleeding at the catheter site, too.
Other types of angiography: Advances in technology have led to other forms of angiography that take less time and mean fewer risks than x-ray angiography. CT angiography takes pictures of blood vessels using a CT scanner instead of a standard x-ray machine. The contrast dye can be put into a small vein in the arm instead of having to put a catheter into a major blood vessel. Magnetic resonance angiography (MRA) is an MRI study of the blood vessels. It may be done with or without contrast dye, and is also quicker than a standard x-ray angiogram.
Intravenous pyelogram (IVP): This x-ray test is used to study kidney function and look for tumors in the urinary tract, although other tests like CT or MRI are more commonly used for this.
You will probably be asked not to eat or drink anything for about 12 hours before the test, and you must take laxatives to clean out your bowel. For the test itself, you lie on a table for a series of x-rays. Contrast dye is then given through a vein in your arm. Your kidneys remove the dye from the bloodstream, and it goes into the urinary tract. Another series of x-rays is taken over the next 30 minutes or so. Pressure may be applied to the belly to help make the image clearer. Once the dye has reached the bladder, you will be asked to pass urine while another x-ray is taken.
Lower GI series (barium enema): This x-ray study is used to look at the lining of the colon (large intestine) and rectum.
Your food may be restricted for a few days before the test. Laxatives and/or enemas are used to clean out the colon. For the test, you lie secured on a table, and a series of x-rays is taken. Then liquid barium is put into your colon through a small, soft tube placed in your rectum. The liquid feels cool. More images are taken while the table tilts you into different positions. You have to lie still and hold your breath as each image is taken. After the test, you can go to the toilet to pass the barium solution out of your bowels. (It may take a few days until it’s all out. Your stool may be drier, harder, and light colored during this time.)
To get clearer pictures, a “double-contrast” exam is often done. This exam uses a smaller amount of thicker barium liquid. After the barium is in, air is put into your bowel. This can cause a sense of fullness and discomfort, along with an urge to empty your bowels.
Upper GI series: This test is used to study the lining of the esophagus (swallowing tube), stomach, and the duodenum (first part of the small intestine).
You will probably be asked to not eat or drink for 8 to 12 hours before the exam. As with the lower GI series, you lie on a tilting table while a series of x-rays are taken. You will need to swallow a barium mixture a few times during the test. (In some cases, substances other than barium are used.) You might also be asked to swallow baking soda crystals to create gas in your stomach. Sometimes pictures are taken a few hours later so the doctor can see the small intestine (it takes time for the barium to move from the stomach to the small intestine). This is called a small bowel follow through. After the test you may be given a laxative to speed up getting the barium out of your body.
Venography: This test can be used to look at veins anywhere in the body. It’s most often used to look for a blood clot in a large vein in the leg or arm (called a deep venous thrombosis or DVT), although other tests are often used first.
As you lie still on the table, the skin over the vein to be used is cleaned and numbed. A catheter (thin plastic tube) is then put into a small vein below the vein that might be blocked (like the foot for a vein in the leg, or the hand for a vein in the arm). It may be threaded in so that it passes into a larger vein closer to the one to be studied, or a tourniquet may be used so the dye flows into the deeper veins. The contrast dye is put in, and a series of x-ray pictures is taken. After that, the catheter is removed. Firm pressure may be needed on the site for a while to make sure it doesn’t bleed.
How long do they take?
- Standard x-ray: about 5 to 10 minutes
- Angiogram: from 1 to 3 hours
- Intravenous pyelogram: about 1 hour
- Lower GI series: 30 to 45 minutes
- Upper GI series: 30 minutes to 6 hours, depending on the part of the digestive system being tested
- Venogram: 30 to 90 minutes
What are the possible complications and side effects of these imaging tests?
Standard x-rays: Problems are rare and very unlikely.
Angiography: You may have a warm or burning feeling as the dye is given. The contrast material may cause nausea, vomiting, flushing, itching, or a bitter or salty taste. In rare cases, people can have a severe allergic reaction to the contrast material that affects their breathing and blood pressure. The contrast material can also cause kidney problems. This is rare, but it’s more common in someone whose kidneys already don’t work well.
There’s a small risk of a blood clot forming on the end of the catheter, which could block a blood vessel. There’s also a small risk of damage to the blood vessel from the catheter, which could lead to internal bleeding. A hematoma (a large collection of blood under the skin) may develop where the catheter was put in if pressure is not kept on the site long enough. (Possible complications of CT or MR angiography are like those described in the sections on CT and MRI).
Intravenous pyelogram (IVP): This test is usually safe, but it should be used with caution (or not at all) in people who are allergic to contrast material with iodine (which also includes CT contrast). The contrast dye causes some people to have nausea, vomiting, flushing, itching, or a bitter or salty taste. In rare cases, people have a severe reaction to the contrast material and need emergency treatment.
Lower GI series (barium enema): The test can be uncomfortable. Some patients have abdominal (belly) cramping. Many patients find the test makes them tired. The barium contrast material will make your stools a light color for a few days after the test and may cause constipation.
Upper GI series (barium swallow): The barium mixture has the thickness of a milkshake and tastes chalky. Baking soda crystals can cause gas and belching. After the test, your stools will be a light color for a few days, and you may be constipated.
Venography: This has similar side effects and possible complications as angiography, although flushing is not as common. There may be pain and bruising where the catheter is put in.
What else should I know about these tests?
- Tell your doctor if you could be pregnant or are breastfeeding before having any of these tests.
- X-ray tests expose the body to radiation, but modern x-ray equipment uses much smaller amounts of radiation than in the past. (See “Questions about radiation risk” for more on this.)
- A newer technology, called digital radiology, produces pictures on computer screens rather than on film. The size and contrast of the pictures can be adjusted to make them easier to read, and they can be sent to computers in other medical offices or hospitals.
- If you are to have a test that uses a contrast dye, tell your doctor if you are allergic to contrast materials, iodine, or to seafood. This may put you at a higher risk for having a reaction.
Last Medical Review: 03/16/2015
Last Revised: 09/15/2015