What is a CT scanner?
A CT scan, sometimes also called a CAT scan, takes pictures of the body and uses a computer to put them together. CT stands for computerized tomography and is a painless procedure. A series of X-rays are taken of the body at slightly different angles, to produce very detailed images of the inside of the body.
The images produced by CT scans are called tomograms and they provide doctors with information to help them reach a diagnosis about a variety of conditions.
Why it is necessary
Because of the way CT images are produced, they have advantages over normal X-ray images in distinguishing between different types of soft tissue.
CT scans can be performed on any part of the head or body and are particularly good for:
- internal organs within the abdomen and chest – liver, kidneys, pancreas, intestines, lungs,
- CT-scan of the breast (breast X-ray) is the absolute best solution for early cancer diagnostics,
- bone imaging – for orthopedic examinations,
- brain imaging – to determine the cause of a stroke, and
- vascular imaging – examining blood flow to different parts of the body.
How the scan machine is working?
When you have a CT scan, you will be required to lie on a motorized bed inside the scanning machine which looks like a giant doughnut.
After each X-ray is completed, the bed on which you are lying is moved forward a small distance You will be asked to lie very still while each scan is taken to avoid blurring the images. Several scans will be carried out and the whole procedure may last up to 30 minutes. If you feel anxious, you may be given a sedative.
A CT scanner uses a series of X-ray beams to build up images of the body in slices. Unlike an X-ray, which sends one beam of radiation through the body, a CT scanner emits a succession of narrow beams as it moves through an arc. This produces a very detailed image that is not possible from a normal X-ray.
The X-ray detector within a CT scanner can see hundreds of different levels of density, including tissues within solid organs such as the liver.
This information can then be sent to a computer, which builds up a cross-sectional image of the body and displays it on the screen.
Depending on the part of the body being examined, a dye (contrast medium) may be used to make some tissues show up more clearly under X-ray. This is commonly used for brain scans to help to show up any tumors. It is also used for scans of the chest, as it enables doctors to find out whether a tumor can be removed with surgery or not.
For scans of the abdomen, you might be given a drink containing barium. This is known as a ‘barium meal’, and shows up white on the scans as it moves through the digestive tract.
CT scanner images: what can we see?
CT scans are commonly performed on the head and abdomen. Head scans are an effective method of checking the head and brain for suspected tumors, bleeding, and swelling of the arteries. They are also useful for investigating the brain following a stroke.
Abdominal CT scans are used to detect tumors and to diagnose conditions in which internal organs are enlarged or inflamed. Tears (lacerations) of the spleen, kidneys or liver, such as may occur in serious road traffic accidents, can be revealed by CT scan.
CT scans may also be used for the following:
- planning radiotherapy treatment regimes,
- assessment of vascular (blood flow) diseases,
- screening for and assessing cardiac (heart) disease,
- assessment of injury and disease to bones, particularly in the spine,
- to find out bone density when investigating osteoporosis,
- guiding biopsy procedures for taking tissue samples.
Risks of a CT scan
CT scans involve exposure to radiation in the form of X-rays. The level of radiation used is kept to a minimum to prevent damage to body cells, and the exposure to radiation depends on the number of images taken. CT scans are quick and accurate, and they eliminate the need for invasive surgery.
The benefits of having a scan are thought to outweigh any risks and it is generally considered very safe.
Pregnant women should not have a CT scan, as there is a small risk that X-rays may cause an abnormality to the unborn child. Be sure to tell your doctor if you think there is a chance that you may be pregnant before having a scan.
The contrast dye used in CT scans often contains iodine, which can cause an allergic reaction in some people.
Important! You should inform the radiologist if you have had an allergic reaction to iodine or a contrast agent in the past, or if you have any other allergies.
Very rarely the dye may cause some kidney damage in people who already have kidney problems. Nursing mothers should wait for 24 hours after contrast injection before resuming breastfeeding.