Imaging or radiology tests create pictures of the chest, abdomen, head, neck and other parts of the body. These tests pass different forms of energy (X-rays, sound waves, radioactive particles or magnetic fields) through your body.
Imaging tests are generally used to detect signs of disease or to check whether cancer (tumors, or masses of cells) has spread to areas such as the lymph nodes, chest or lungs. Your doctor may order an imaging test "with contrast," which makes it easier to see certain organs and tissues in the body. This means that before your test, the technician injects a contrast dye into one of your veins or a port or asks you to drink a liquid containing the dye. If you've had a reaction to contrast dye or iodine in the past, tell your doctor or the technician.
Your doctor will give you specific pretest instructions. Let him or know if you are or might be pregnant, because many imaging tests use small amounts of radiation.
Types of Imaging Tests
A chest X-ray produces images of the chest, lungs, heart, large arteries, ribs and diaphragm. Doctors use chest X-rays to detect signs of disease, including infection or tumors. An X-ray that shows an abnormal fluid collection can be a sign of infection, such as pneumonia or tuberculosis, or a tumor. It can also show evidence of enlarged lymph nodes or signs of internal injury.
How Is It Done? You'll be asked to wear a gown during the procedure and remove all jewelry. A technician positions you in front of the X-ray machine. You must hold your breath for a few seconds while the technician takes the X-ray; he or she will explain in detail what you need to do. Two images are usually taken, one from the back of the chest and another from the side.
An ultrasound, also called a sonography, uses high-frequency sound waves to create pictures of internal organs, tissue and blood flow. Unlike other X-rays and computed tomography (CT) scans, ultrasound doesn't use radiation. Doctors use ultrasound to:
- detect cysts, tumors, organ damage following illness and other medical problems
- evaluate symptoms like pain, swelling and infection
- This noninvasive procedure is commonly used by obstetricians to view a developing baby in the womb or by cardiologists (heart specialists) to evaluate a pumping heart's function.
How Is It Done? Follow your doctor's instructions for preparing for an ultrasound. For some scans, your doctor may tell you not to eat or drink for up to 12 hours before the test. For others, you may be told to drink up to eight glasses of water one to two hours before the exam and not to urinate so your bladder is full for the scan.
When you undergo the ultrasound, the technician applies a lubricant (jelly) to the area of your body to be examined. This helps the technician slide the wandlike, handheld instrument across your skin. The instrument transmits sound waves to create pictures on a screen. The technician slides the device around the body area while viewing and capturing different images.
Computed Tomography (CT) Scans
A computed tomography (CT) scan shows a cross-section of the body using multiple images. CT scans are different than standard X-rays because they create a series of pictures taken from different angles and produce much clearer images. A CT scan of the chest or abdomen can help detect an enlarged lymph node or cancers in the liver, pancreas, lungs, bones and spleen. The noninvasive test is also used to monitor a tumor's response to therapy or detect a return of cancer after treatment.
How Is It Done? If your abdominal area is to be scanned, your doctor may prescribe laxatives, enemas or suppositories or a temporary change in your diet before the scan to cleanse the bowel. In some cases, you may be asked not to eat or drink for several hours before the exam.
If you're anxious about being strapped down or confined in a small space, tell your doctor or the technician. Some patients are given a mild sedative before the test to help them relax. Before the exam, contrast dye, if needed, is usually injected into a vein in your hand or arm.
A CT scan normally takes between 10 and 30 minutes. You'll be asked to wear a gown during the procedure and remove any jewelry or metal objects. The technician positions you on the CT exam table, usually by having you lie flat on your back. The table is connected to a scanner with a round, doughnut-shaped hole in the middle. To determine the correct starting position, the table moves through the scanner quickly. When the actual scan begins, the machine rotates around you, taking a series of images. It's important that you hold still during the exam. The technician may use pillows or straps to help you remain still. You may be asked to hold and release your breath during the scan.
Once the scan is completed, you may be asked to wait while the radiologist checks to see whether more images are needed.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is a noninvasive procedure that provides detailed pictures of internal organs, soft tissues, blood vessels and bones. MR images are made with a large magnet, radio waves and a computer and can show signs of disease (tumors, or masses of cells). MRI can also detect bone changes, common in some forms of cancer such as myeloma, earlier than conventional X-ray studies can.
How Is It Done? If you're anxious about being strapped down or confined in a small space, tell your doctor or the technician. Some patients are given a mild sedative before the test to help them relax. Having the test with an open MRI machine may be another option. Before the exam, contrast dye, if needed, is usually injected into a vein in your hand or arm.
The procedure is painless and normally takes between 15 and 45 minutes, depending on the area being scanned. You may be asked to remove any jewelry or metal objects and wear a gown during the procedure or you may be allowed to remain in loose-fitting clothing as long as they have no zippers or metal accessories.
The technician positions you on the MRI exam table, which slides into a machine shaped like a tunnel. It's important that you hold still during the exam. As multiple images are taken, you'll hear a series of loud knocking sounds.
Fluorodeoxyglucose with Positron Emission Tomography
Fluorodeoxyglucose with positron emission tomography (FDG-PET) is an effective tool for detecting lymphoma and other cancers. The test uses a radioactive glucose (sugar) molecule, called FDG, to produce images that show your tissues' metabolism (function). Because tumor cells require more glucose than normal cells do to survive and multiply, doctors can identify cells as cancerous when they consume significantly large amounts of glucose. Tumors as small as one centimeter can be detected during FDG-PET. The test also provides a sensitive and relatively rapid assessment of your response to therapy.
How Is It Done? If you're anxious about being strapped down or confined in a small space, tell your doctor or the technician. Some patients are given a mild sedative before the test to help them relax. You usually have to fast (not eat) before the test to make sure your blood sugar level isn't high.
Before the PET scan, the technician injects you with FDG containing a radioactive tracer. It takes 30 to 60 minutes for the radioactive glucose to travel through the body and be absorbed by the organ or tissue being studied. You may feel a cold sensation move up your arm when the radioactive tracer is injected, but there are generally no side effects. The amount of exposure to radiation is small.
The procedure is painless and takes about 45 minutes. You may be asked to remove any jewelry or metal objects and wear a gown during the scan or you may be allowed to remain in loose-fitting clothing as long as they have no zippers or metal accessories. The technician positions you on the PET exam table, which slides into a large scanner with a round, doughnut-shaped hole in the middle. It's important that you hold still during the exam.
After the scan is completed, you may be asked to wait while the radiologist checks to see whether more images are needed.