A CT (computerised tomography) scan is a special kind of X-ray. Instead of sending out a single X-ray through your body as with ordinary X-rays, several beams are sent simultaneously from different angles. This allows more detailed images from within the body to be constructed, and these images are then interpreted by a doctor. CT scans may also be referred to as CAT scans (computerised axial tomography). Unlike an MRI scanner, where you are placed within a tunnel, a CT scanner consists of a doughnut shaped machine and therefore you should not feel claustrophobic
When it is used?
CT scans are far more detailed than ordinary X-rays. The information from the two-dimensional computer images can be reconstructed to produce three-dimensional images. It is used for taking pictures of virtually any part of the body.
They can be used to produce virtual images that show what a surgeon would see during an operation. They are used for a variety of different reasons, mainly because CT imaging is one of the best and fastest tools for examining the chest, abdomen and pelvis, and because it can provide cross-sectional views and highly detailed images.
Some of the most common uses of CT imaging include detecting different types of cancer (for example in the lung, bowel, liver and kidney), examining patients with severe injuries(trauma) and finding the cause for sudden rapid onset symptoms (such as breathlessness, abdominal pain).
CT is also used for the detection, diagnosis and treatment of a number of vascular disease, which may ultimately lead to stroke, kidney failure or blood clots in the lungs.
This also includes abdominal aortic anueryms (AAAs), which is where the large main artery running downwards in the abdomen becomes enlarged and therefore may be prone to spontaneously rupture.
CT is also used to diagnosing and analysing many spinal problems and injuries which may occur to the hands, feet and other skeletal structures.
This is because CT is good, not just for looking at soft tissue structures, but also in providing detailed images of even very small bones.
CT scans also allows doctors to inspect the inside of the body without having to operate or perform unpleasant examinations.
It allows surgeons to plan surgery prior to starting a procedure, and allows assessment of the results after a procedure has been performed.
CT scanning has also proven invaluable in pinpointing exactly where a tumour is and planning treatment with radiotherapy.
The scanner is particularly good at testing for bleeding in the brain, for aneurysms (when the wall of an artery swells up), brain tumours and brain damage. It can also find tumours and abscesses throughout the body and is used to assess types of lung disease.
In addition, the CT scanner is used to look at internal injuries such as a torn kidney, spleen or liver; or bony injury, particularly in the spine. CT scanning can also be used to guide biopsies and therapeutic pain relieving procedures.
CT scan is also used to detect disease in chest(CT Chest) and also Cardiac CT which is a painless test that uses an x-ray machine to take clear, detailed pictures of the heart. Doctors use this test to look for heart problems.
How it works?
The X-rays from the beams are detected after they have passed through the body and their strength is measured.
Beams that have passed through less dense tissue such as the lungs will be stronger, whereas beams that have passed through denser tissue such as bone will be weaker.
A computer can use this information to work out the relative density of the tissues examined. Each set of measurements made by the scanner is, in effect, a cross-section through the body. . During the test, you will lie on a table that is attached to the CT scanner, which is a large doughnut-shaped machine. The CT scanner sends X-rays . Each rotation of the scanner provides a picture of a thin slice. One part of the scanning machine can tilt to take pictures from different positions. All of the pictures are saved as a group on a computer.
In some cases, a dye called contrast material may be put in a vein (IV) in your arm or into the spinal canal. The dye makes structures and organs easier to see on the CT pictures. The dye may be used to check blood flow and look for tumors, areas of inflammation, or nerve damage
The scan is a non-invasive, painless medical procedure. It usually takes approximately 10 to 30 minutes to perform, depending on the part of the body that is being scanned, the number of pictures taken and the different angles required.
The scanner itself looks like a large doughnut, with a bed passing through it. During the scan the patient lies on a bed, with the body part under examination placed in the round tunnel or opening of the scanner.
If contrast material is to be used it will either be swallowed, injected via an intravenous line (IV) or administered by enema. How contrast is given depends on the type of examination to be carried out. The patient will usually be asked to hold their breath during the scan. This is because any kind of motion, such as breathing or body movement, can lead to degradation of the resulting image and so make it harder to analyse and interpret.
The bed then moves slowly backwards and forwards to allow the scanner to take pictures of the body, although it does not touch the patient.
During the scan, only the patient will be in the exam room during the time the scan is carried out, unless there are special circumstances, such as a parent needing to stay in the room with their child, in which case they are required to wear a lead apron to minimise the radiation exposure.
During the scan, the technician will communicate with the patient via a speaker in the scan room, and they will be able to hear and see the patient at all times.
Instructions to the patients
Patients should always be asked about any recent illnesses or medical conditions they may have, and whether there is a history of heart disease, asthma, diabetes, kidney disease or thyroid problems.
Prior to starting the procedure, the patient will usually be given a gown to hospital gown to wear. It is important that metal objects, such as jewellery, eyeglasses, dentures and hairpins, are removed before starting the procedure, since these will affect the quality of the images. The patient may also be asked to remove hearing aids and dental work, and women will be asked to remove bras containing metal underwire. Where possible, piercings should also be removed.
If a patient is going to have a contrast injection, he or she should not have anything to eat or drink for a 4-6 hours before the CT scan because the injection may cause stomach upset. 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 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.
If the patient is receiving an abdomen scan, for example, they will be asked not to eat for 4-6 hours before the test. They will be given a drink of oral contrast/water for a period of 45 minutes to 1hour before the procedure.
This makes the intestines easier to see on the pictures. Sometimes a liquid X-ray dye is injected into the veins during the test. This also makes it easier to see the organs, blood vessels or, for example, a tumour.
The injection might be a little uncomfortable, and some people also experience a feeling of warmth in their arm. It’s important the patient inform their doctor prior to the administration of a contrast agent, if they have had a known allergy to contrast material, or ‘dye’.
The risk is greatest to those who are pregnant, as radiation exposure can cause harm to the fetus, and therefore CT scans are contraindicated in pregnant women, unless the benefits of performing the scan far outweigh the risks.
Some patients may experience side-effects due to allergic reactions to the liquid dye injected into the veins.
In very rare cases, this dye has been known to damage already weakened kidneys.
It is important to let the X-ray doctors or technicians know if you have any allergies, asthma or kidney trouble, prior to having the X-ray dye injected.
Please get all the old x-rays, sonography, CT & MR films along with the other papers,operative notes,discharge card etc relevant to the case.