Computed tomography (CT) is a type of imaging. It uses special x-ray equipment to make cross-sectional pictures of your body.

Doctors use CT scans to look for:

  • Broken bones
  • Cancers
  • Blood clots
  • Signs of heart disease
  • 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.

Tests and Procedures

A computerized tomography (CT) scan combines a series of X-ray images taken from different angles and uses computer processing to create cross-sectional images, or slices, of the bones, blood vessels and soft tissues inside your body.

CT scan images provide more detailed information than plain X-rays do.
A CT scan has many uses, but is particularly well-suited to quickly examine people who may have internal injuries from car accidents or other types of trauma. A CT scan can be used to visualize nearly all parts of the body and is used to diagnose disease or injury as well as to plan medical, surgical or radiation treatment.

Your doctor may recommend a CT scan to help:

  • Diagnose muscle and bone disorders, such as bone tumors and fractures
  • Pinpoint the location of a tumor, infection or blood clot
  • Guide procedures such as surgery, biopsy and radiation therapy
  • Detect and monitor diseases and conditions such as cancer, heart disease, lung nodules and liver masses
  • Monitor the effectiveness of certain treatments, such as cancer treatment
  • Detect internal injuries and internal bleeding

During a CT scan, you’re briefly exposed to ionizing radiation. The amount of radiation is greater than you would get during a plain X-ray because the CT scan gathers more detailed information. CT scans have not been shown to cause long-term harm, although there may be a very small potential to increase your risk of cancer.

CT scans have many benefits that outweigh this small potential risk. Doctors use the lowest dose of radiation possible to obtain the needed medical information. Also, newer, faster machines and techniques require less radiation than was previously used. Talk with your doctor about the benefits and risks of your CT scan.

Harm to Unborn Babies

Tell your doctor if you’re pregnant. Although the radiation from a CT scan is unlikely to injure your baby, your doctor may recommend another type of exam, such as ultrasound or MRI, to avoid exposing your baby to radiation.

Reactions to Contrast Material

In certain cases, your doctor may recommend you receive a special dye called a contrast material through a vein in your arm before your CT scan. Although rare, the contrast material can cause medical problems or allergic reactions.

Most reactions are mild and result in a rash or itchiness. In rare instances, an allergic reaction can be serious, even life-threatening. Tell your doctor if you’ve ever had a reaction to contrast material.

Depending on which part of your body is being scanned, you may be asked to:

  • Take off some or all of your clothing and wear a hospital gown
  • Remove metal objects, such as a belt, jewelry, dentures and eyeglasses, which might interfere with image results
  • Refrain from eating or drinking for a few hours before your scan

Contrast Material

A special dye called a contrast material is needed for some CT scans, to help highlight the areas of your body being examined. The contrast material blocks X-rays and appears white on images, which can help emphasize blood vessels, intestines or other structures.

Contrast material might be given to you:

  • By mouth. If your esophagus or stomach is being scanned, you may need to swallow a liquid that contains contrast material. This drink may taste unpleasant.
  • By injection. Contrast agents can be injected through a vein in your arm to help your gallbladder, urinary tract, liver or blood vessels stand out on the images. You may experience a feeling of warmth during the injection or a metallic taste in your mouth.
  • By enema. A contrast material may be inserted in your rectum to help visualize your intestines. This procedure can make you feel bloated and uncomfortable.

Preparing Your Child for a Scan

If your infant or toddler is having a CT scan, the doctor may recommend a sedative to keep your child calm and still. Movement blurs the images and may lead to inaccurate results. Ask your doctor how to prepare your child.

You can have a CT scan done in a hospital or an outpatient facility. CT scans are painless and, with newer machines, take only a few minutes. The whole procedure typically takes about 30 minutes.

During the CT Scan

CT scanners are shaped like a large doughnut standing on its side. You lie on a narrow, motorized table that slides through the opening into a tunnel. Straps and pillows may be used to help you stay in position. During a head scan, the table may be fitted with a special cradle that holds your head still.

While the table moves you into the scanner, detectors and the X-ray tube rotate around you. Each rotation yields several images of thin slices of your body. You may hear buzzing, clicking and whirring noises.

A technologist in a separate room can see and hear you. You will be able to communicate with the technologist via intercom. The technologist may ask you to hold your breath at certain points to avoid blurring the images.

After the CT Scan

After the exam you can return to your normal routine. If you were given a contrast material, you may receive special instructions. In some cases, you may be asked to wait for a short time before leaving to ensure that you feel well after the exam. After the scan, you’ll likely be told to drink lots of fluids to help your kidneys remove the contrast material from your body.

CT images are stored as electronic data files and are usually reviewed on a computer screen. A radiologist interprets these images and sends a report to your doctor.

Specific Examinations

Doctors use chest CT scans to:

  • Show the size, shape, and position of your lungs and other structures in your chest.
  • Follow up on abnormal findings from standard chest x rays.
  • Find the cause of lung symptoms, such as shortness of breath or chest pain.
  • Find out whether you have a lung problem, such as a tumor, excess fluid around the lungs, or a pulmonary embolism (a blood clot in the lungs). The test also is used to check for other conditions, such as tuberculosis (tu-ber-kyu-LO-sis), emphysema (em-fi-SE-ma), and pneumonia (nu-MO-ne-ah).

The chest CT scanning machine takes many pictures, called slices, of the lungs and the inside of the chest. A computer processes these pictures; they can be viewed on a screen or printed on film. The computer also can stack the pictures to create a very detailed, three-dimensional (3D) model of organs.

What is CT Scanning of the Spine?

CT images of internal organs, bones, soft tissue and blood vessels typically provide greater detail than traditional x-rays, particularly of soft tissues and blood vessels.

Using CT, the bony structure of the spinal vertebrae is clearly and accurately shown, as are the intervertebral disks and, to some degree, the spinal cord.

What are some common uses of the procedure?

Perhaps, the most frequent use of spinal CT is to detect—or to rule out—spinal column damage in patients who have been injured.

CT scanning of the spine is also performed to:

  • Evaluate the spine before and after surgery.
  • Help diagnose spinal pain. One of the most common causes of spinal pain that may be diagnosed by CT is a herniatedintervertebral disk. Occasionally, this diagnosis is made using CT myelography.
  • Accurately measure bone density in the spine and predict whether vertebral fractures are likely to occur in patients who are at risk of osteoporosis.
  • Assess for congenital anomalies of the spine or scoliosis.
  • Detect various types of tumors in the vertebral column, including those that have spread there from another area of the body. Some tumors that arise elsewhere are first identified by finding deposits of malignant cells (metastases) in the vertebrae; prostate cancer is an example.
  • Guide diagnostic procedures such as the biopsy of a suspicious area to detect cancer, or the removal of fluid from a localized infection (abscess).

In patients with narrowing (stenosis) of the spinal canal, vertebral fracture, infection or degenerative disease such as arthritis, CT of the spine may provide important information when performed alone or in addition to magnetic resonance imaging (MRI).

What is CT Scanning of the Head?

CT scanning provides more detailed information on head injuries, stroke, brain tumors and other brain diseases than regular radiographs (x-rays).

What are some common uses of the procedure?

CT scanning of the head is typically used to detect:

  • Bleeding, brain injury and skull fractures in patients with head injuries.
  • Bleeding caused by a ruptured or leaking aneurysm in a patient with a sudden severe headache.
  • A blood clot or bleeding within the brain shortly after a patient exhibits symptoms of a stroke.
  • A stroke, especially with a new technique called Perfusion CT.
  • Brain tumors.
  • Enlarged brain cavities (ventricles) in patients with hydrocephalus.
  • Diseases or malformations of the skull.

CT scanning is also performed to:

  • Evaluate the extent of bone and soft tissue damage in patients with facial trauma, and planning surgical reconstruction.
  • Diagnose diseases of the temporal bone on the side of the skull, which may be causing hearing problems.
  • Determine whether inflammation or other changes are present in the paranasal sinuses.
  • Plan radiation therapy for cancer of the brain or other tissues.
  • Guide the passage of a needle used to obtain a tissue sample (biopsy) from the brain.
  • Assess aneurysms or arteriovenous malformations through a technique called CT angiography.

What is CT (Computed Tomography) of the Sinuses?

A CT scan of the face produces images that also show a patient’s paranasal sinus cavities. The paranasal sinuses are hollow, air-filled spaces located within the bones of the face and surrounding the nasal cavity, a system of air channels connecting the nose with the back of the throat. There are four pairs of sinuses, each connected to the nasal cavity by small openings.

What are some common uses of the procedure?

CT of the sinuses primarily is used to:

  • Detect the presence of inflammatory diseases.
  • Plan for surgery by defining anatomy or giving further information about tumors of the nasal cavity and sinuses.
  • Evaluate sinuses that are filled with fluid or thickened sinus membranes.
  • Help diagnose sinusitis.

What are some common uses of the procedure?

This procedure is typically used to help diagnose the cause of abdominal or pelvic pain and diseases of the internal organs, smallbowel and colon, such as:

  • Infections such as appendicitis, pyelonephritis or infected fluid collections, also known as abscesses.
  • Inflammatory bowel disease such as ulcerative colitis or Crohn’s disease, pancreatitis or liver cirrhosis.
  • Cancers of the liver, kidneys, pancreas, ovaries and bladder as well as lymphoma.
  • Kidney and bladder stones.
  • Abdominal aortic aneurysms (AAA), injuries to abdominal organs such as the spleen, liver, kidneys or other internal organs in cases of trauma.
    CT scanning of the abdomen/pelvis is also performed to:
  • Guide biopsies and other procedures such as abscess drainages and minimally invasive tumor treatments.
  • Plan for and assess the results of surgery, such as organ transplants.
  • Stage, plan and properly administer radiation treatments for tumors as well as monitor response to chemotherapy.

What are some common uses of the procedure?

CT imaging is:

  • One of the fastest and most accurate tools for examining the chest, abdomen and pelvis because it provides detailed, cross-sectional views of all types of tissue.
  • Uused to examine patients with injuries from trauma such as a motor vehicle accident.
  • Performed on patients with acute symptoms such as chest or abdominal pain or difficulty breathing.
  • Often the best method for detecting many different cancers, such as lymphoma and cancers of the lung, liver, kidney, ovary and pancreas since the image allows a physician to confirm the presence of a tumor, measure its size, identify its precise location and determine the extent of its involvement with other nearby tissue.
  • An examination that plays a significant role in the detection, diagnosis and treatment of vascular diseases that can lead to stroke, kidney failure or even death. CT is commonly used to assess for pulmonary embolism (a blood clot in the lung vessels) as well as for aortic aneurysms.
  • Invaluable in diagnosing and treating spinal problems and injuries to the hands, feet and other skeletal structures because it can clearly show even very small bones as well as surrounding tissues such as muscle and blood vessels.

In pediatric patients, CT imaging is often used to evaluate:

  • Lymphoma
  • Neuroblastoma
  • Kidney tumors
  • Congenital malformations of the heart, kidneys and blood vessels
  • Cystic fibrosis
  • Complications of acute appendicitis
  • Complications of pneumonia
  • Inflammatory bowel disease
  • Severe injuries

Physicians often use the CT examination to:

  • Quickly identify injuries to the lungs, heart and vessels, liver, spleen, kidneys, bowel or other internal organs in cases of trauma.
  • Guide biopsies and other procedures such as abscess drainages and minimally invasive tumor treatments.
  • Plan for and assess the results of surgery, such as organ transplants or gastric bypass.
  • Stage, plan and properly administer radiation treatments for tumors as well as monitor response to chemotherapy.
  • Measure bone mineral density for the detection of osteoporosis.

What is CT Angiography?

Angiography is a minimally invasive medical test that helps physicians diagnose and treat medical conditions. Angiography uses one of three imaging technologies and, in most cases, a contrast material injection is needed to produce pictures of blood vessels in the body.

Angiography is performed using:

  • X-Rays with catheters
  • Computed tomography (CT)
  • Magnetic resonance imaging (MRI)

CT angiography uses a CT scanner to produce detailed images of both blood vessels and tissues in various parts of the body. An iodine-rich contrast material (dye) is usually injected through a small catheter placed in a vein of the arm. A CT scan is then performed while the contrast flows through the blood vessels to the various organs of the body. After scanning, the images will be processed using a special computer and software and reviewed in different planes and projections.

What are some common uses of the procedure?

CT angiography is used to examine blood vessels and the organs supplied by them in various body parts, including:

  • Brain
  • Neck
  • Heart
  • Chest
  • Abdomen (such as the kidneys and liver)
  • Pelvis
  • Legs and feet
  • Arms and hands

Physicians use this test to diagnose and evaluate many diseases of blood vessels and related conditions such as:

  • Injury
  • Aneurysms
  • Blockages (including those from blood clots or plaques)
  • Disorganized blood vessels and blood supply to tumors
  • Congenital (birth related) abnormalities of the heart, blood vessels or various parts of the body which might be supplied by abnormal blood vessels

Also, physicians use this exam to check blood vessels following surgery, such as:

  • Identify abnormalities, such as aneurysms, in the aorta, both in the chest and abdomen, or in other arteries.
  • Detect atherosclerotic (plaque) disease in the carotid artery of the neck, which may limit blood flow to the brain and cause a stroke.
  • Identify a small aneurysm or arteriovenous malformation (abnormal communications between blood vessels) inside the brain or other parts of the body.
  • Detect atherosclerotic disease that has narrowed the arteries to the legs and help prepare for endovascular intervention or surgery.
  • Detect disease in the arteries to the kidneys or visualize blood flow to help prepare for a kidney transplant.
  • Guide interventional radiologists and surgeons making repairs to diseased blood vessels, such as implanting stents or evaluating a stent after implantation.
  • Detect injury to one or more arteries in the neck, chest, abdomen, pelvis or extremities in patients after trauma.
  • Evaluate arteries feeding a tumor prior to surgery or other procedures such as chemoembolization or selective internal radiation therapy.
  • Identify dissection or splitting in the aorta in the chest or abdomen or its major branches.
  • Show the extent and severity of the effects of coronary artery disease and plan for a surgical operation, such as a coronary bypass and stenting.
  • Examine pulmonary arteries in the lungs to detect pulmonary embolism (blood clots, such as those traveling from leg veins) or pulmonary arteriovenous malformations.
  • Look at congenital abnormalities in blood vessels, especially arteries in children (e.g., malformations in the heart or other blood vessels due to congenital heart disease).
  • Evaluate obstructions of vessels.

What is CT Enterography?

CT enterography is a special type of computed tomography (CT) imaging performed with intravenous contrast material after the ingestion of liquid that helps produce high resolution images of the small intestine in addition to the other structures in the abdomen and pelvis.

What are some common uses of the procedure?

Physicians use CT enterography to identify and locate:

  • Small bowel inflammation
  • Bleeding sources within the small bowel
  • Small bowel tumors
  • Abscesses and fistulas
  • Bowel obstruction.

CT enterography is also used to diagnose Crohn’s disease, and determine its location, severity and unexpected complications, in order to guide effective treatment.

What is CT Perfusion of the Head?

Computed tomography (CT) perfusion imaging shows which areas of the brain are supplied or perfused adequately with blood and provides detailed information on delivery of blood or blood flow to the brain.

CT perfusion scanning is a noninvasive medical test that helps physicians diagnose and treat medical conditions.

What are some common uses of the procedure?

CT perfusion is typically used to:

  • Evaluate acute stroke.
  • Assist with selecting patients for thrombolytic therapy following a stroke by identifying brain tissue at risk of infarction, or death by lack of an adequate blood supply.
  • Evaluate vasospasm, or a sudden blood vessel constriction that may arise from a subarachnoid hemorrhage, in which bleeding occurs in the space between the two membranes surrounding the brain, known as the dura mater and arachnoid membrane.
  • Assess patients who are candidates for surgical or neuroendovascular treatments. The technique employs special catheters (long, thin tubes), some containing special instruments, that can be manipulated into the area of vessel blockage to dissolve or dislodge a blood clot.
  • Diagnose and assess treatment response in patients with a variety of tumors.

What is Urography?

Urography is an examination used to evaluate the kidneys, ureters and bladder. Excretory urography, also known as intravenous pyelogram, is performed using conventional x-ray after the intravenous administration of radiographic contrast material. This technique is still performed for pediatric patients and for younger adult patients.

Computed tomography (CT) urography and magnetic resonance (MR) urography use CT and MR images, respectively, after intravenous contrast material to obtain images of the urinary tract. CT urography (CTU) and MR urography (MRU) are used as primary imaging techniques to evaluate patients with blood in the urine (hematuria), follow patients with prior history of cancers of the urinary collecting system and to identify abnormalities in patients with recurrent urinary tract infections. In addition to imaging the urinary tract, CT and MR urography can provide valuable information about other abdominal and pelvic structures and diseases that may affect them.

What are some common uses of the procedure?

Urography images are used to evaluate issues or detect abnormalities in portions of the urinary tract, including the kidneys, bladder and ureters, including:

  • Hematuria (blood in urine)
  • Kidney or bladder stones
  • Cancers of the urinary tract

What is virtual colonoscopy?

Virtual colonoscopy, also called computerized tomography (CT) colonography, is a procedure that uses a combination of x rays and computer technology to create images of the rectum and entire colon. Virtual colonoscopy can show irritated and swollen tissue, ulcers, and polyps—extra pieces of tissue that grow on the lining of the intestine.

This procedure is different from colonoscopy, which uses a long, flexible, narrow tube with a light and tiny camera on one end, called a colonoscope or scope, to look inside the rectum and entire colon.

What are the rectum and colon?

The rectum and colon are part of the gastrointestinal (GI) tract, a series of hollow organs joined in a long, twisting tube from the mouth to the anus, a 1-inch-long opening through which stool leaves the body. The body digests food using the movement of muscles in the GI tract, along with the release of hormones and enzymes. Organs that make up the GI tract are the mouth, esophagus, stomach, small intestine, large intestine—which includes the appendix, cecum, colon, and rectum—and anus. The intestines are sometimes called the bowel. The last part of the GI tract—called the lower GI tract—consists of the large intestine and anus.

The GI tract

The large intestine is about 5 feet long in adults and absorbs water and any remaining nutrients from partially digested food passed from the small intestine. The large intestine then changes waste from liquid to a solid matter called stool. Stool passes from the colon to the rectum. The rectum is 6 to 8 inches long in adults and is located between the last part of the colon—called the sigmoid colon—and the anus. The rectum stores stool prior to a bowel movement. During a bowel movement, stool moves from the rectum to the anus.

Why is a virtual colonoscopy performed?

A virtual colonoscopy is performed to help diagnose

  • Changes in bowel habits
  • Abdominal pain
  • Bleeding from the anus
  • Weight loss

A gastroenterologist—a doctor who specializes in digestive diseases—may also order a virtual colonoscopy as a screening test for colon cancer. Screening is testing for diseases when people have no symptoms. Screening may find a disease at an early stage, when a gastroenterologist has a better chance of curing the disease.

A gastroenterologist may recommend earlier screening for people with a family history of colon cancer, a personal history of inflammatory bowel disease—a long-lasting disorder that causes irritation and sores in the GI tract—or other risk factors for colon cancer.

How does a person prepare for a virtual colonoscopy?

Preparation for a virtual colonoscopy includes the following steps:

  • Talk with a gastroenterologist. When people schedule a virtual colonoscopy, they should talk with their gastroenterologist about medical conditions they have and all prescribed and over-the-counter medications, vitamins, and supplements they take, including
    • Aspirin or medications that contain aspirin
    • Nonsteroidal anti-inflammatory drugs such as ibuprofen or naproxen
    • Arthritis medications
    • Blood thinners
    • Diabetes medications
    • Vitamins that contain iron or iron supplementsWomen should let their gastroenterologist know if they are pregnant. Developing fetuses are particularly sensitive to x rays. The x-ray technician should take special precautions to minimize exposure, or the gastroenterologist may suggest an alternative procedure, such as a colonoscopy.
  • Cleanse the bowel. The gastroenterologist will give written bowel prep instructions to follow at home. A gastroenterologist orders a bowel prep so that little to no stool is present inside the person’s intestine. A complete bowel prep lets the person pass stool that is clear. Stool inside the colon can prevent the CT scanner from taking clear images of the intestinal lining. Instructions may include following a clear liquid diet for 1 to 3 days before the procedure and avoiding drinks that contain red or purple dye. The instructions will provide specific direction about when to start and stop the clear liquid diet. People may drink or eat the following:
    • Fat-free bouillon or broth
    • Strained fruit juice, such as apple or white grape—orange juice is not recommended
    • Water
    • Plain coffee or tea, without cream or milk
    • Sports drinks in flavors such as lemon, lime, or orange
    • Gelatin in flavors such as lemon, lime, or orange
  • Drink contrast medium. The night before the procedure, the person will drink a liquid that contains a special dye, called contrast medium. Contrast medium is visible on x rays and can help distinguish between stool and polyps.