A computerised tomography (CT) scan uses X-rays and a computer to create detailed images of the inside of the body.
CT scans are also sometimes known as CAT scans, or computed tomography scans.
During a CT scan, you’ll usually lie on your back on a flat bed. The CT scanner consists of an X-ray tube that rotates around your body. You’ll usually be moved continuously through this rotating beam.
The X-rays will be received by a detector on the opposite side of your body and an image of the scan will be produced by a computer.
Unlike an MRI scan, where you’re placed inside a tunnel, you shouldn’t feel claustrophobic.
The images produced by a CT scan are called tomograms and are more detailed than standard X-rays. A CT scan can produce images of structures inside the body, including the internal organs, blood vessels, bones and tumours.
The scan is painless and will usually take between five and 10 minutes depending on the part of your body being scanned.
WHEN CT SCANS ARE USED
CT scans can be used to diagnose and monitor a variety of different health conditions, including brain tumours, certain bone conditions, and injuries to internal organs such as the kidneys, liver or spleen. They’re also now being used to look at the heart.
They’re also often used to look inside the body before another procedure takes place, such as radiotherapy treatment or a biopsy (where a small sample of tissue is taken so that it can be examined under a microscope).
CT scans are only used when the doctor responsible for your care decides there’s a clear medical benefit.
Although CT scans are generally safe, they do expose you to slightly more radiation than other types of imaging tests. The amount of radiation you’re exposed to can vary depending on the type of scan you have.
In most cases, the benefits outweigh any potential risks because a CT scan can provide your doctor with much clearer images than those produced by a normal X-ray.
However, CT scans aren’t routinely recommended for pregnant women because there’s a risk that the X-rays could harm the unborn baby.
Children are also more at risk of developing a build-up of radiation than adults. A CT scan will therefore only be recommended if a child has a serious condition that puts them at greater risk.
WHY ARE CT SCANS PERFORMED?
CT scans are performed to analyze the internal structures of various parts of the body. This includes the head, where traumatic injuries, (such as blood clots or skull fractures), tumors, and infections can be identified. In the spine, the bony structure of the vertebrae can be accurately defined, as can the anatomy of the intervertebral discs and spinal cord. In fact, CT scan methods can be used to accurately measure the density of bone in evaluating osteoporosis.
Occasionally, contrast material (an X-ray dye) is placed into the spinal fluid to further enhance the scan and the various structural relationships of the spine, the spinal cord, and its nerves. Contrast material is also often administered intravenously or through other routes prior to obtaining a CT scan (see below). CT scans are also used in the chest to identify tumors, cysts, or infections that may be suspected on a chest X-ray. CT scans of the abdomen are extremely helpful in defining body organ anatomy, including visualizing the liver, gallbladder, pancreas, spleen, aorta, kidneys, uterus, and ovaries. CT scans in this area are used to verify the presence or absence of tumors, infection, abnormal anatomy, or changes of the body caused by trauma.
The technique is painless and can provide extremely accurate images of body structures in addition to guiding the radiologist in performing certain procedures, such as biopsies of suspected cancers, removal of internal body fluids for various tests, and the draining of abscesses which are deep in the body. Many of these procedures are minimally invasive and have markedly decreased the need to perform surgery to accomplish the same goal.
ARE THERE RISKS IN OBTAINING A CT SCAN?
A CT scan is a very low-risk procedure. The most common problem is an adverse reaction to intravenous contrast material. Intravenous contrast is usually an iodine-based liquid given in the vein, which makes many organs and structures, such as the kidneys and blood vessels, much more visible on the CT scan. There may be resulting itching, a rash, hives, or a feeling of warmth throughout the body. These are usually self-limiting reactions that go away rather quickly. If needed, antihistamines can be given to help relieve the symptoms. A more serious allergic reaction to intravenous contrast is called an anaphylactic reaction. When this occurs, the patient may experience severe hives and/or extreme difficulty in breathing. This reaction is quite rare, but is potentially life-threatening if not treated. Medications which may include corticosteroids, antihistamines, and epinephrine can reverse this adverse reaction.
Toxicity to the kidneys which can result in kidney failure is an extremely rare complication of the intravenous contrast material used in CT scans. People with diabetes, people who are dehydrated, or patients who already have impaired kidney function are most prone to this reaction. Newer intravenous contrast agents have been developed, such as Isovue, which have nearly eliminated this complication.
The amount of radiation a person receives during a CT scan is minimal. In men and nonpregnant women, it has not been shown to produce any adverse effects. If a woman is pregnant, there may be a potential risk to the fetus, especially in the first trimester of the pregnancy. If a woman is pregnant, she should inform her doctor of her condition and discuss other potential methods of imaging, such as an ultrasound, which are not harmful to the fetus. However, the the radiation exposure during a CT scan may cause a very small increase in a person’s lifetime risk of developing cancer. This concern is often viewed as more important for children, because the cancer risk per dose of radiation is higher for younger patients than adults, and younger patients have a longer life expectancy. Still, the risks of exposure to radiation must be weighed against the benefits of using CT scanning to diagnose or treat illness. CT scanners can be modified to deliver exposures that are more appropriate for pediatric patients. Most physicians suggest that all radiation exposure to patients should be kept to a minimum; those patients that “doctor shop” or repeatedly go to emergency departments for a “CT” put themselves at risk for radiation-caused problems.