What is a CT scan?
In medical terms, a computerised tomography (CT) scan creates a series of pictures which can be used to visualize the inside of the body, including internal organs and blood vessels, as well as parts of the musculoskeletal system, such as bones.
All CT scans are performed by a specialist called a radiologist using a computerised tomography scanner. The radiologist then analyzes the images and produces a radiology report to give to the doctor who ordered the scan. CT scans, in general, are painless. Although the scan itself is usually quick (10-30 minutes), it is important to check with the practice how long the appointment will last, as some scans may take much longer than others. The process can be undergone as an outpatient.
Doctors can use radiology reports to accurately diagnose a wide range of conditions like fractures, bone structure diseases, cancer and cardiovascular disease much earlier in their course than would be possible by many other means.
When are CT scans used?
Doctors can use radiology reports produced from CT scans to diagnose a wide range of conditions affecting the organs, bones and tissues of the body, often much earlier on in their course than would be possible by non-imaging means. Conditions commonly diagnosed with the aid of CT scans include:
- Blood flow problems
- Widened, weakened blood vessels (aneurysms)
- Cardiovascular disease
- Musculoskeletal disorders (in general) and damage to bones (in particular)
- Trauma effects to organs or musculoskeletal structures
- Infectious disease
Radiology reports help doctors to establish the need for further tests, or to decide on appropriate treatment methods. For example, the report could enable a doctor to identify where to take a needle biopsy; this is a procedure in which a small amount of sample tissue is removed from the body using a needle, or to plan the best approach for the surgical repair of a complicated fracture. CT scans are also useful for monitoring how effectively a course of treatment is working. For example, a cancer patient receiving radiotherapy may undergo periodic CT scans.
How to prepare for a CT scan
On the day of the procedure, the person undergoing a CT will be asked to remove their clothing, jewelry and any other metal objects, such as a removable mouth-brace. A loose gown will be provided by the hospital. If they feel anxious about the scan, a sedative, medication which relaxes and calms individuals, may be provided. A sedative may also be prescribed if the person being scanned is a young child, or for anybody who experiences difficulties remaining still.
Before undergoing the CT scan , individuals may be given a contrast material. This is a dye which highlights the specific blood vessels, tissues or organs being examined, making them stand out from the rest of the body. Contrast material is usually given through a drip in a vein in the arm.
Contrast material is normally harmless and passes out of the body during urination following the scan, within a few hours to a day. However, some people may experience adverse reactions to contrast material. Before administering it, doctors will check a person’s clinical history to make sure whether it is suitable.
If a person has a history of asthma, or previous allergic reactions to contrast material, the chances of experiencing an adverse reaction are increased. Adverse reactions to contrast material include non-severe allergic reactions like nausea, vomiting and skin reactions, such as rashes or swelling and, much less commonly, kidney damage and anaphylactic reactions*, the latter being an emergency, a severe allergic reaction. Kidney damage is more common in people who have previously experienced kidney problems.
Unlike severe allergic reactions, it is very common to experience a tingling sensation or feeling of warmth as the contrast material spreads in one’s body, but this is nothing to be worried about.
Good to know: There is a commonly held misconception that allergies to iodine-rich substances – including antiseptics and foods such as seafood – hold cross-reactivity with contrast material containing iodine, meaning people are more likely to be allergic to contrast material if they are allergic to these substances. This has been shown not to be the case, and therefore these patients very likely won’t react negatively to the contrast material.
What happens during a CT scan?
The CT scanner is made up of a scanning device, a large ring containing X-ray equipment, and a motorized bed. During a CT scan, the individual lies down on the bed and remains as still as possible.
Although the technologist operating the scanner will be in a separate room, one can communicate with them throughout the procedure, using an intercom system. The technologist may ask the person undergoing the scan to perform certain simple actions such as breathing in and out at certain moments. These actions help the technologist to create images which are as clear as possible.
What happens after a CT scan?
Following the scan, the images that are collected are processed by a computer. The radiologist will analyze the images, taking into account the medical history of the individual and any suspected diagnoses, and produce a radiology report. The report will usually be passed to the doctor who ordered the scan, and they will be responsible for discussing it with the individual. It is normal to wait days or sometimes even a few weeks to receive the results of a CT scan.
CT scans are generally painless and non-invasive , i.e.not requiring the introduction of instruments into the body, so most people do not experience any adverse effects. In most cases, individuals should be able to leave the hospital when the scan is complete. If no sedatives or contrast material were used, day-to-day activities can be continued as normal. If a contrast material was used, a wait in the hospital of roughly an hour or two may be necessary in order to monitor for signs of an allergic reaction. Sometimes these allergic reactions, especially the ones affecting the skin, may be quite delayed. In this case, or when in doubt, it is always best to contact one’s doctor to be safe.
If a sedative was used, a friend or family member will normally be asked to accompany the individual home, and they should avoid driving or operating machinery for the rest of the day.
CT scan FAQs
Q: How is a CT scan different from an MRI scan?
A: The principal difference between CT scans and MRI (magnetic resonance imaging) scans is that CT scans use X-rays to produce their images, while MRI scans use radio frequency pulses and magnetic fields. The MRI scanner is shaped like a tube and surrounds the whole body at once. An MRI scanner is more likely to make a person feel claustrophobic than the ring-shaped CT scanner. However, the images produced by MRI scans have the potential to reveal any difference between normal and abnormal non-skeletal tissue more clearly than images from a CT scan.
For someone who has been prescribed a scan, there are several factors to consider in order to decide whether a CT scan or an MRI scan is the most suitable option for their needs. The doctor will decide whether CT or MRI scanning is suitable on a case-by-case basis.
Q: Are the X-rays from the CT scanner dangerous?
A: Exposure to the high-intensity radiation involved in X-rays is associated with an increased risk of developing cancer later on. It is therefore advisable to limit the number of X-rays performed on a person to what is absolutely necessary. To combat the risk of cancer from exposure to radiation, CT scanners have sophisticated radiation dose controls. Furthermore, it is possible to opt for a low-dose radiation X-ray/CT scan in cases where a lesser-quality CT scan image will be sufficient to make a diagnosis. The radiation-related risks associated with CT scans are far outweighed by their benefits. CT scans give doctors the ability to rapidly make correct diagnoses and prescribe appropriate treatments for otherwise unidentifiable or much harder or only much later identifiable conditions.
Q: Does an angiogram involve a CT scan?
A: An angiogram may involve a CT scan, depending on the type of angiography technique recommended by a person’s doctor. Angiography is used to look at the blood vessels and to detect any problems related to blood flow around the body. CT angiography (CTA) is an imaging technique which produces pictures of virtual slices of the body, which can be used to examine blood flow and related problems. It is also possible to examine the blood vessels using magnetic resonance imaging (MRI) angiography.
An important advantage of CT angiography over MRI angiography is that it is possible for the radiologist to view and evaluate bones, soft tissues and blood vessels all at the same time. This increases the possibility that a single angiography session will be enough to reveal everything that the doctor needs to know in order to accurately diagnose and properly treat the affected person.
Other names for CT scan
- CAT scan (computerized axial tomography scan)
“Adverse Reactions to Contrast Material: Recognition, Prevention, Treatment].” American Family Physician. October 2002. Accessed: 25 February 2018. ↩ ↩