A computerised tomography (CT) scan uses X-rays and a computer to create detailed images of the inside of the body. CT scans are sometimes referred to as CAT scans or computed tomography scans. They're carried out in hospital by specially trained operators called radiographers, and can be done while you're staying in hospital or during a short visit. CT scans can produce detailed images of many structures inside the body, including the internal organs, blood vessels and bones. They can be used to: CT scans wouldn't normally be used to check for problems if you don't have any symptoms (known as screening). This is because the benefits of screening may not outweigh the risks, particularly if it leads to unnecessary testing and anxiety. Your appointment letter will mention anything you need to do to prepare for your scan. You may be advised to avoid eating anything for several hours before your appointment to help make sure clear images are taken. You should contact the hospital after receiving your appointment letter if you have any allergies or kidney problems, or if you're taking medication for diabetes, as special arrangements may need to be made. You should also let the hospital know if you're pregnant. CT scans aren't usually recommended for pregnant women unless it's an emergency, as there's a small chance the X-rays could harm your baby. It's a good idea to wear loose, comfortable clothes as you may be able to wear these during the scan. Try to avoid wearing jewellery and clothes containing metal (such as zips), as these will need to be removed. Before having the scan, you may be given a special dye called a contrast to help improve the quality of the images. This may be swallowed in the form of a drink, passed into your bottom (enema), or injected into a blood vessel. Tell the radiographer if you feel anxious or claustrophobic about having the scan. They can give you advice to help you feel calm and can arrange for you to have a sedative (medication to help you relax) if necessary. Before the scan starts, you may be asked to remove your clothing and put on a gown. You'll also be asked to remove anything metal, such as jewellery, as metal interferes with the scanning equipment. During the scan, you'll usually lie on your back on a flat bed that passes into the CT scanner. The scanner consists of a ring that rotates around a small section of your body as you pass through it. Unlike an MRI scan, the scanner doesn't surround your whole body at once, so you shouldn't feel claustrophobic. The radiographer will operate the scanner from the next room. While the scan is taking place, you'll be able to hear and speak to them through an intercom. While each scan is taken, you'll need to lie very still and breathe normally. This ensures that the scan images aren't blurred. You may be asked to breathe in, breathe out, or hold your breath at certain points. The scan will usually take around 10 to 20 minutes. You shouldn't experience any after-effects from a CT scan and can usually go home soon afterwards. You can eat and drink, go to work and drive as normal. If a contrast was used, you may be advised to wait in the hospital for up to an hour to make sure you don't have a reaction to it. The contrast is normally completely harmless and will pass out of your body in your urine. Your scan results won't usually be available immediately. A computer will need to process the information from your scan, which will then be analysed by a radiologist (a specialist in interpreting images of the body). After analysing the images, the radiologist will write a report and send it to the doctor who referred you for the scan so they can discuss the results with you. This normally takes a few days or weeks. CT scans are quick, painless and generally safe. But there's a small risk you could have an allergic reaction to the contrast dye used and you'll be exposed to X-ray radiation. The amount of radiation you're exposed to during a CT scan varies, depending on how much of your body is scanned. CT scanners are designed to make sure you're not exposed to unnecessarily high levels. Generally, the amount of radiation you're exposed to during each scan is equivalent to between a few months and a few years of exposure to natural radiation from the environment. It's thought exposure to radiation during CT scans could slightly increase your chances of developing cancer many years later, although this risk is thought to be very small (less than 1 in 2,000). For more information, read GOV.UK: patient dose information. The benefits and risks of having a CT scan will always be weighed up before it's recommended. Talk to your doctor or radiographer about the potential risks beforehand if you have any concerns.
Page last reviewed: 18 August 2021
Computed tomography is commonly referred to as a CT scan. A CT scan is a diagnostic imaging procedure that uses a combination of X-rays and computer technology to produce images of the inside of the body. It shows detailed images of any part of the body, including the bones, muscles, fat, organs and blood vessels. CT scans are more detailed than standard X-rays. In standard X-rays, a beam of energy is aimed at the body part being studied. A plate behind the body part captures the variations of the energy beam after it passes through skin, bone, muscle and other tissue. While much information can be obtained from a regular X-ray, a lot of detail about internal organs and other structures is not available. In CT, the X-ray beam moves in a circle around the body. This allows many different views of the same organ or structure and provides much greater detail. The X-ray information is sent to a computer that interprets the X-ray data and displays it in two-dimensional form on a monitor. Newer technology and computer software makes three-dimensional images possible. CT scans may be performed to help diagnose tumors, investigate internal bleeding, or check for other internal injuries or damage. CT can also be used for a tissue or fluid biopsy.
CT scans may be done with or without contrast. Contrast refers to a substance taken by mouth or injected into an IV line that causes the particular organ or tissue under study to be seen more clearly. Contrast examinations may require you to fast for a certain period of time before the procedure. Your doctor will notify you of this prior to the procedure. You will need to let your doctor know if you have ever had a reaction to any contrast media and/or any kidney problems. A reported seafood allergy is not considered to be a contraindication for iodinated contrast. If you have any medical conditions or recent illnesses, inform your doctor.
If you are having a computed tomography angiography (CTA) or a virtual colonoscopy, you will be given specific instructions when you make your appointment. PRECAUTIONS: If you are pregnant or think you may be pregnant, please check with your doctor before scheduling the exam. CLOTHING: You may be asked to change into a patient gown. If so, a gown will be provided for you. Please remove all piercings and leave all jewelry and valuables at home. CONTRAST MEDIA: Contrast may be indicated for your exam. The contrast media improves the radiologist’s ability to find structures that are abnormal and understand normal anatomy better.
ALLERGY: Please inform the access center representative when you schedule your scan if you have had an allergic reaction to any contrast media. IV contrast will not be administered if you have had a severe or anaphylactic reaction to any contrast media in the past. Mild to moderate reactions warrant a plan that includes taking medication prior to the CT examination. These plans will be discussed with you in detail when you schedule your exam. Any known reactions to a contrast media should be discussed with your personal physician. EAT/DRINK: If your study was ordered without contrast, you can eat, drink and take your prescribed medications prior to your exam. If your doctor orders a CT scan with contrast, do not eat anything three hours prior to your CT scan. We encourage you to drink clear liquids. You may also take your prescribed medications prior to your exam. DIABETICS: People with diabetes should eat a light breakfast or lunch three hours prior to the scan time. Depending on your oral medication for diabetes, you may be asked to discontinue use of the medication for 48 hours after the CT examination. Detailed instructions will be given following your examination. MEDICATION: All patients can take their prescribed medications as usual. A new CT scanner will change the management and outcomes of coronary artery disease. The CT scan captures images of the heart between beats, leading to clearer images to help detect anatomic and functional characteristics of coronary artery disease. This technology can also be used to help replace invasive tests to determine which patients with chest pain need intervention.
If you are pregnant or think you may be pregnant, you should notify your health care provider. The amount of radiation dose used in a CT scan is small. You may want to ask your doctor about the amount of radiation used during the CT procedure and the risks related to your particular situation. If you are claustrophobic or tend to become anxious easily, tell your doctor ahead of time. You may be prescribed a mild sedative to take before the procedure to make you more comfortable. What happens during a CT scan?CT scans may be performed on an outpatient basis or as part of your stay in a hospital. Procedures may vary depending on your condition and your physician’s practices. Generally, CT scans follow this process:
What happens after a CT scan?
What are some of the advances in CT technology?Advances in CT technology include:
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