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Types of CT Scans

CT Scanning of the Abdomen

CT imaging of the abdomen is an examination that uses x-rays to visualize several types of tissue with great clarity, including organs such as the liver, spleen, pancreas and kidneys. Using specialized equipment and expertise to create and interpret CT scans of the lower gastrointestinal (GI) tract, the colon and rectum, an experienced radiologist can accurately diagnose many causes of abdominal pain, such as an abscess in the abdomen, inflamed colon or colon cancer, diverticulitis and appendicitis. Often, no additional diagnostic work-up is necessary and treatment planning can begin immediately.

CT is often the preferred method for diagnosing many different cancers, including colon cancer, since the image allows a physician to confirm the presence of a tumor and to measure its size, precise location, and the extent of the tumor's involvement with other nearby tissue. CT examinations of the lower GI tract can be used to plan and properly administer radiation treatments for tumors, and to guide biopsies and other minimally invasive procedures. CT can also play a significant role in the detection, diagnosis and treatment of vascular disorders that can lead to stroke, gangrene or kidney failure.

The technologist begins by positioning the patient on the CT table. The patient's body is generally supported by specially molded pillows to help the patient remain still and in the proper position during the scan. As the study proceeds, the table will move slowly into the CT scanner. The increments of movement may be so small that they are almost undetectable, or large enough that the patient feels the sensation of motion depending on the body part being examined.

A CT examination of the gastrointestinal tract requires the use of a contrast material to enhance the visibility of certain tissues. Before administering the contrast material, the radiologist or technologist will ask whether the patient has any allergies, especially to medications or iodine, and whether the patient has a history of diabetes, asthma, a heart condition, kidney problems or thyroid conditions. These conditions may indicate a higher risk of reaction to the contrast material or potential problems eliminating the material from the patient's system after the exam.

A CT examination usually takes from five minutes to half an hour. When the exam is over, the patient may be asked to wait until the images are examined to determine if more images are needed.

CT Angiography

CT (computed tomography) angiography (CTA) is an examination that uses x-rays to visualize blood flow in arterial vessels throughout the body, from arteries serving the brain to those bringing blood to the lungs, kidneys, and the arms and legs.

CTA is commonly used to:

  • Examine the pulmonary arteries in the lungs to rule out pulmonary embolism, a serious but treatable condition.
  • Visualize blood flow in the renal arteries (those supplying the kidneys) in patients with high blood pressure (hypertension) and those suspected of having kidney disorders. Narrowing (stenosis) of a renal artery is a cause of high blood pressure in some patients, and can be corrected. A special computerized method of viewing the images makes CT renal angiography a very accurate examination. It is also done in prospective kidney donors.
  • Identify aneurysms in the aorta or in other major blood vessels. Aneurysms are diseased areas of a weakened blood vessel wall that bulges out like a bulge in a tire. Aneurysms are life-threatening because they can rupture.
  • Identify dissection in the aorta or its major branches. Dissection means that the layers of the artery wall peel away from each other like the layers of an onion. Dissection can cause pain and can be life-threatening.
  • Identify a small aneurysm or arterio-venous malformation inside the brain which can be life-threatening.
  • Detect atherosclerotic disease that has narrowed the arteries to the legs.
  • CTA also is used to detect narrowing or obstruction of arteries in the pelvis and in the carotid arteries bringing blood from the heart to the brain.
  • Proper function of a stent that has been placed to restore blood flow in a diseased artery, CT angiography will show whether it is serving its purpose.

Most of the time a CTA examination is spent setting everything up. Actually recording the images takes only seconds. After changing into a gown and having an IV set up, you will answer questions about things that might complicate the exam (such as allergies) and then will lie down on a narrow table. The part of your body to be examined will be placed inside the opening of the CT unit with the aid of criss-crossed positioning lights. A test image is taken to determine the best position, and a small dose of contrast material is given to see how long it takes to reach the area under study. Then the IV is hooked up to an automatic injector, contrast material is injected, and the scan begins. Afterwards, the images will be reviewed and, if necessary, some will be repeated. No special measures are needed after the procedure.

CTA takes about 10 to 25 minutes from the time the actual examination begins. Overall, you can expect to be in or near the examining room for 20 to 30 minutes. You may feel warm all over when contrast material is injected before the scan, but you should not feel pain at any time. Any CT study requires that you remain still during the exam. Pillows and foam pads may help make it more comfortable. At the same time the nurse or technologist may use pads or Velcro straps to keep the area from moving. The examination table will move into and out of the scanner opening, but it is not enclosed and only a small part of your body will be inside at any one time. You may be asked to hold your breath for 10 to 25 seconds to be sure that the images will not be blurred. During the time that no actual imaging is taking place you are free to ask questions or talk to the technologist, but friends or relatives will not be allowed in the examining room. Once the needed images have been recorded, you will be free to leave. You can eat immediately and it is a good idea to drink plenty of fluids in the hours after the exam to help flush contrast material out of the system.

CT Scanning of the Chest

CT scanning of the chest uses special equipment to obtain multiple cross-sectional images of the organs and tissues of the chest. CT produces images that are far more detailed than a conventional chest x-ray. CT is especially useful because it can simultaneously show many different types of tissue including the lungs, heart, bones, soft tissues, muscle and blood vessels.

CT of the chest is used to take a closer look at findings detected on conventional chest x-rays or may be used to investigate and try to explain clinical signs or symptoms of disease of the chest. The CT examination may provide more specific information regarding the nature and extent of the findings or, in some cases, determine that the chest is normal.

CT may be used to detect and evaluate the extent of tumors that arise in the lung and mediastinum, or tumors that have spread there from other parts of the body. CT is routinely used to assess whether tumors are responding to treatment.

You may have heard that, in recent years, some people have chosen to have a chest CT scan to screen for lung cancer. This makes the most sense for those who are former or current cigarette smokers, as they are at much greater risk of cancer than are nonsmokers. The best hope of curing lung cancer is to find it as early as possible, making it easier to treat. CT is able to detect even very small abnormalities that could be early lung cancer, which would not be visible on a conventional chest x-ray. A special low-dose CT technique is used for lung cancer screening. CT of the chest is not able to detect every cancer.

Chest CT also can demonstrate other lung disorders such as old or new pneumonia, tuberculosis, emphysema, bronchiectasis, and diffuse interstitial lung disease. When the clinical findings and regular chest x-ray are inconclusive, CT may clarify the situation. Inflammation or other diseases of the pleura, the membrane covering the lungs, can be seen in CT images.

Accident victims and other people with chest injury often have a CT exam to assess damage to organs, bones (including the spinal column), and to large blood vessels.
An aneurysm, or ballooning out of the aorta, may be found totally unexpectedly when chest CT is done for other reasons. Or a CT scan may be used to confirm suspicion of aneurysm on the basis of a plain chest x-ray. It is important to be aware of this condition so that it may be watched and, if necessary, treated before rupturing.

CT is used to detect blood clots that travel from the deep veins in the legs and lodge in the pulmonary arteries, blocking the normal blood flow to the lungs. This condition, called pulmonary embolism, is usually seen in patients who are immobile for long periods of time or who have cancer or clotting disorders. Pulmonary embolisms can be life threatening if not detected and treated. When pulmonary embolism is suspected, a special type of CT scan is performed called a CT Angiogram (CTA). This involves injecting the iodine into a vein a little faster and also more numerous and thinner slices are made through the chest in order to see the arteries in the lungs.

The first step is for the technologist to make certain that you are correctly positioned on the CT table. Pillows may be used to help maintain the correct position during the examination. For the initial scans, the table will move rapidly through the scanner to determine the correct starting position. The rest of the scans are made as the table moves more slowly through the cavity in the scanner. The best chest CT scans are obtained when you are able to hold your breath. If this is not possible, you will be asked to breathe quietly and regularly.

CT scanning is a pain-free procedure. If contrast material is injected you may feel a flush of heat or a metallic taste in your mouth, usually lasting no more than a minute or two. You also may notice mild itching. If this persists or hives develop, effective medication is available. Very rarely a patient becomes short of breath or has swelling in the throat or another part of the body, indicating a more serious reaction to contrast material that must be promptly treated. If you experience any of these symptoms, inform the technologist immediately.

You will be alone during the scan, but the technologist can see and hear you and can speak to you at any time from the adjacent control room. The examination usually takes 15 to 30 minutes, including preparation time. The actual scan time is less than 30 seconds.

CT Scanning of the Head

CT scanning of the head is an examination that provides detailed information on head injuries, brain tumors, and other brain diseases. It also can show bone, soft tissues, and blood vessels in the same images.

CT of the head can assist in:

  • locating skull fractures and brain damage in patients with head injuries.
  • detecting a blood clot or bleeding within the brain shortly after a patient exhibits symptoms of a stroke.
  • determining the extent of bone and soft tissue damage in patients with facial trauma, and planning surgical reconstruction.
  • detecting and localizing bleeding in a patient with sudden severe headache who may have a ruptured or leaking aneurysm.
  • detecting some brain tumors.
  • diagnosing diseases of the temporal bone on the side of the skull, which may cause hearing problems.
  • illuminating enlarged brain cavities (ventricles) in patients with hydrocephalus.
  • determining whether inflammation or other changes are present in the paranasal sinuses.
  • planning radiation therapy for cancer of the brain or other tissues.
  • guiding the passage of a needle used to obtain a tissue sample (biopsy) from the brain.
  • non-invasively assessing for aneurysms or arteriovenous malformations through a technique called CT angiography.
  • detecting diseases or malformations of the skull.
  • three-dimensional imaging of the skull and brain structures.

CT scanning of the head may be performed in the hospital or at an outpatient radiology center, but in either case your doctor must give you a written referral with the reason why the study should be performed. You will lie on a table that is guided into the center of the scanner, and you will be asked to lie very still.
As stated earlier, some patients will require an injection of a contrast material to enhance the visibility of certain tissues or blood vessels. A small needle connected to an intravenous line is placed in an arm or hand vein. The contrast material will be injected through this line.

Depending on the number of images needed, a CT exam of the head and brain can take between two and 45 minutes. When it is completed you will be asked to wait until the technologist examines the images to determine if more are needed.

When you enter the scanner, special lights may be turned on to ensure correct positioning. Some exams (such as a scan of the sinuses) call for a special head holder that uses soft straps to keep the head and neck in proper alignment. In some cases you will lie on your stomach; in others on your back. The patient and technologist can talk at any time via an intercom.

CT itself causes no pain, though there may be some discomfort from the need to remain still. If contrast material is injected you may have a warm, flushed sensation during the injection. You may also experience a metallic taste in your mouth that lasts for about two minutes. Occasionally a patient will develop itching and hives for up to a few hours after the injection; this can be relieved by medication. If you develop light-headedness or difficulty breathing, it may indicate a more severe allergic reaction a physician or nurse will be present to assist you.

CT Scanning of the Spine

CT scanning of the spine is a type of x-ray examination that uses a scanner to obtain multiple images of the spinal column, as well as three-dimensional images if needed. CT images are far more detailed than those obtained by a conventional x-ray unit. In addition, CT is a very useful diagnostic method because it can display and distinguish many different types of tissue in the same region, including bone, muscle, soft tissue and blood vessels. The bony structure of the spinal vertebrae is clearly and accurately shown by CT scanning, as are the intervertebral disks and, to some degree, the spinal cord.

Some of the common uses of the procedure include:

  • To detect or rule out spinal damage in patients who have been injured.
  • The spine before and after surgery.
  • To 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.
  • To detect narrowing of the spinal canal, vertebral fracture, infection, or degenerative disease such as arthritis, CT of the spine may provide important information when carried out by itself or in addition to magnetic resonance imaging (MRI). One of the most common causes of spinal pain that may be diagnosed by CT is a herniated intervertebral disk.

Spinal CT scanning is carried out with the patient lying on his or her back. The technologist will make sure that you are properly positioned, and may use pillows to help you maintain a correct posture during the study. If indicated, a contrast material will be injected into an arm vein during the procedure so as to sharpen the images of various tissues. A scan of the lower spine may also be done after injecting contrast material into the spinal canal surrounding the spinal cord during a lumbar puncture. This will help to detect tumors or locate areas of inflammation or nerve compression. Initially the table will move rapidly through the scanner to determine the correct starting position. Further scans then are made as the table moves more slowly through the tunnel in the scanner.

The actual imaging takes only a very short time and a complete exam, including set-up time, takes from five to 30 minutes. When the exam is completed, you may have to wait a short time while the radiologist checks the images to be sure that they are of high enough quality to be correctly interpreted. If necessary, a few additional scans will be obtained. Less patient movement during the procedure produces clearer CT images.

Spinal CT scanning is a painless procedure, apart from a needle stick if an intravenous injection is needed. Discomfort comes mainly from having to lie still on the table for some time. Injection of contrast material may cause a slight burning feeling in the arm, a metallic taste, and warm flushing of the entire body. These all are normal reactions and usually end within a few seconds.

Risks

  • CT does involve exposure to radiation in the form of x-ray, but the benefit of an accurate diagnosis far outweighs the risk.
  • Special care is taken during x-ray examinations to ensure maximum safety for the patient by shielding the abdomen and pelvis with a lead apron, with the exception of those examinations in which the abdomen and pelvis are being imaged. Women should always inform their doctor or x-ray technologist if there is any possibility that they are pregnant.
  • Nursing mothers should wait for 24 hours after contrast material injection before resuming breast feeding.
  • There is a risk of an allergic reaction which may be serious whenever contrast material containing iodine is injected. If you have a history of allergy to x-ray dye, your radiologist may advise that you take special medication for 24 hours before the exam to lessen the risk of allergic reaction. Another option is to undergo a different exam that does not call for contrast injection.
  • Contrast injection should be avoided in patients with kidney disease or severe diabetes because x-ray contrast material can further harm kidney function.
  • If a large amount of x-ray contrast leaks out under the skin where the IV is placed, skin damage can result. If you feel any pain in this area during contrast injection, you should immediately inform the technologist.