Whole Body Spiral CT
Why would you have a CT Scan?
CT scanning is advanced radiological imaging that uses an x-ray beam that rotates around the patient to capture pictures inside the body. CT images are useful in studies of internal organs because they can separate overlapping structures precisely, producing cross-sectional images of all parts of the body. The CT scanner also is useful in determining the size and volume of tumors and other masses. This is especially helpful for cancer patients undergoing radiation therapy or surgery.
If one looks at a standard X-ray image or radiograph (such as a chest X-ray), it appears as if they are looking through the body. CT and MRI are similar to each other, but provide a much different view of the body than an X-ray does. CT produce cross-sectional images that appear to open the body up, allowing the doctor to look at it from the inside. Plain X-rays are an inexpensive, quick test and are accurate at diagnosing things such as pneumonia, arthritis, and fractures. CT is better to evaluate soft tissues such as the brain, liver, and abdominal organs, as well as to visualize subtle abnormalities that may not be apparent on regular X-ray tests.
What are some common uses of the procedure?
Because it provides detailed, cross-sectional views of all types of tissue, CT is one of the best tools for studying the brain, chest, abdomen, and pelvis. It is often the preferred method for diagnosing many different cancers, including lung, liver, and pancreatic 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 are often used to plan and properly administer radiation treatments for tumors, and to guide biopsies and other minimally invasive procedures.
CT can clearly show even very small bones, as well as surrounding tissues such as muscle and blood vessels. This makes it invaluable in diagnosing and treating spinal problems and injuries to the hands, feet, and other skeletal structures. CT images can also be used to measure bone mineral density for the detection of osteoporosis. In cases of trauma, CT can quickly identify injuries to the liver, spleen, kidneys, or other internal organs. Many dedicated shock-trauma centers have a CT scanner in the trauma department. CT can also play a significant role in the detection, diagnosis, and treatment of vascular diseases that can lead to stroke, heart attack, gangrene or kidney failure.
- A head or brain CT is used to evaluate the various structures of the brain to look for a mass, stroke, area of bleeding, or blood vessel abnormality. It is also sometimes used to look at the skull.
- A neck CT checks the soft tissues of the neck and is frequently used to study a lump or mass in the neck or to look for enlarged lymph nodes or glands.
- CT of the chest is frequently used to further study an abnormality on a plain chest X-ray. It is also often used to look for enlarged lymph nodes.
- Abdominal and pelvic CT looks at the abdominal and pelvic organs (such as the liver, spleen, kidneys, pancreas, and adrenal glands) and the gastrointestinal tract. These studies are often ordered to check for a cause of pain and sometimes to follow up on an abnormality seen on another test such as an ultrasound.
- A sinus CT exam is used to both diagnose sinus disease and to detect a narrowing or obstruction in the sinus drainage pathway.
- A spine CT test is most commonly used to detect a herniated disc or narrowing of the spinal canal (spinal stenosis) in people with neck, arm, back, and/or leg pain. It is also used to detect a fracture or break in the spine.
How should I prepare for the procedure?
You should wear comfortable, loose-fitting clothing for your CT exam. Metal objects can affect the image, so avoid clothing with zippers and snaps. You may will also be asked to remove hairpins, jewelry, eyeglasses, hearing aids, and any removable dental work, depending on the part of the body that is being scanned. You may be asked not to eat or drink anything for one or more hours before the exam. Women should always inform their doctor or x-ray technologist if there is any possibility that they are pregnant.
How does the procedure work?
In many ways, CT scanning works very much like other x-ray examinations. Very small, controlled amounts of x-ray radiation are passed through the body, and different tissues absorb radiation at different rates. With plain radiology, when special film is exposed to the absorbed x-rays, an image of the inside of the body is captured. With CT, the film is replaced by an array of detectors, which measure the x-ray profile.
Inside the CT scanner is a rotating gantry that has an x-ray tube mounted on one side and an arc-shaped detector mounted on the opposite side. An x-ray beam is emitted in a fan shape as the rotating frame spins the x-ray tube and detector around the patient. Each time the x-ray tube and detector make a 360° rotation and the x-ray passes through the patient’s body, the image of a thin section is acquired. During each rotation, the detector records about 1,000 images (profiles) of the expanded x-ray beam. Each profile is then reconstructed by a dedicated computer into a 3-dimensional image of the section that was scanned.
The Aquilion 16 has an extremely rapid gantry rotation of 400 milliseconds. It also slices down to 0.5 millimeters allowing for the most sensitive and rapid imaging available today.
You might think of it like looking into a loaf of bread by cutting it into thin slices. When the image slices are reassembled by computer, the result is a very detailed, multidimensional view of the body’s interior.
Spiral (helical) 3D CT has improved the accuracy of CT for many diseases. A new vascular imaging technique – spiral CT angiography – is noninvasive and less expensive than conventional angiography, and allows doctors to see blood vessels without the need for more invasive procedures.
The term “spiral CT” comes from the shape of the path taken by the x-ray beam during scanning. The examination table advances at a constant rate through the scanner gantry while the x-ray tube rotates continuously around the patient, tracing a spiral path through the patient. This spiral path gathers continuous data with no gaps between images.
With spiral CT, refinements in detector technology support faster, higher-quality image acquisition with less radiation exposure. It is typically eight to 10 times faster than conventional CT. Such speed is beneficial in all patients but especially in elderly, pediatric, or critically ill patients, populations in which the length of scanning was often problematic. A spiral scan can usually be obtained during a single breath hold.
With conventional CT, small lesions may frequently go undetected when a patient breathes differently on consecutive scans, as a lesion may be missed by unequal spacing between scans. The speed of spiral scanning and single breath hold increases the rate of lesion detection.
CECT Scan Preparation
- If a patient is going to have a contrast injection, he or she should not have anything to eat or drink for a few hours before the CT scan because the injection may cause stomach upset. To receive the contrast injection, an IV is inserted into the arm just prior to the scan. The contrast then enters the body through the IV.
- Prior to most CT scans of the abdomen and pelvis, it is important to drink an oral contrast agent that contains dilute barium. This contrast agent helps the radiologist identify the gastrointestinal tract (stomach, small and large bowel), detect abnormalities of these organs, and to separate these structures from other structures within the abdomen. The patient will be asked to drink slightly less than a quart spread out over 1.5 to 2 hours.
- The biggest potential risk is with a contrast (also called dye) injection that is sometimes used in CT scanning. This contrast can help distinguish normal tissues from abnormal tissues. It also helps to help distinguish blood vessels from other structures such as lymph nodes. Like any medication, some people can have a serious allergic reaction to the contrast. The chance of a fatal reaction to the contrast is about 1 in 100,000.
Anyone who has had a prior contrast reaction or severe allergic reaction to other medications, has asthma or emphysema, or has severe heart disease is at increased risk for a contrast reaction.
During the Procedure
Most CT scans are conducted as an outpatient procedure. Since they do not require hospitalization, the patient has the test and then goes home.
- The CT scanner looks like a large donut with a narrow table in the middle. Unlike MRI, in which the patient would be placed inside the tunnel of the scanner, when undergoing a CT scan, the patient rarely experiences claustrophobia because of the openness of the doughnut shape of the scanner. Typically the patient lies on their back on the table, which moves through the center of the machine. The patient moves through the scanner either head first or feet first, depending on the part of the body being scanned. For certain scans such as sinuses and middle ear, the patient would lie on their stomach and go through head first.
- The patient must remain motionless for the length of the study, which is typically just a few minutes. The entire procedure, which includes set-up, the scan itself, checking the pictures, and removing the IV if needed, takes 15 to 45 minutes depending on what part of the body is being scanned.
- For some studies, the patient will be asked to hold their breath for up to 20 seconds.
- No metal may be worn.
- What clothing the patient wears depends on the nature of the study. For a CT scan of the chest, abdomen, or pelvis, for example, usually the patient will change into a hospital gown. For a head CT scan, the patient can wear normal street clothes.
- The technologist is in the next room and can observe the patient through a large window.
After the Procedure
If the patient received a contrast injection, the IV is removed from the arm before going home. There should be no ill effects from the scan or the contrast injection. In the rare circumstance that the patient received sedation, they will be sent home once they are awake and alert. However, someone will have to drive the patient home.
The CT scan is interpreted by a radiologist, a medical doctor trained to interpret various X-ray studies. The results are forwarded to the doctor. How soon the doctor receives the report depends on the imaging center where the study is performed.
What are the benefits vs. risks?
- Unlike other imaging methods, CT scanning offers detailed views of many types of tissue,including the lung, bones,soft tissues, and blood vessels.
- CT examinations are fast and simple. Especially in trauma cases, they can reveal internal injuries and bleeding quickly enough to help save lives.
- CT scanning can identify both normal and abnormal structures, making it a useful tool to guide radiotherapy, needle biopsies, and other minimally invasive procedures.
- CT scanning is painless, noninvasive, and accurate.
- Diagnosis made with the assistance of CT can eliminate the need for invasive exploratory surgery and surgical biopsy.
- CT has been shown to be a cost-effective imaging tool for a wide range of clinical problems.
- CT does involve exposure to radiation in the form of x-rays, but the benefit of an accurate diagnosis far outweighs the risk. The typical radiation dose from a CT exam is equivalent to the amount of natural background radiation received over a year’s time. Among all radiological procedures, radiation exposure from CT of the body is intermediate.
- 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 injection before resuming breast feeding.
- The risk of serious allergic reaction to iodine-containing contrast material is rare, and radiology departments are well equipped to deal with them.