CT Scan (Head)
What is a CT scan of the head?
CT scans of the head (also called a cranial CT scans or computed tomography scans) are used to diagnose and monitor conditions affecting the brain and head, such as strokes, bleeding inside the head and brain tumors. Computerized tomography scanning for the head is an alternative imaging process to other means of imaging the head and brain, such as magnetic resonance imaging (MRI) scanning and X-rays. A person’s doctor will recommend whether computerized tomography, or another type of imaging, is best, depending on a person’s individual needs.
All computerized tomography scans are performed by a specialist called a radiologist using a computerized tomography scanner. The radiologist (a doctor specialising in scans) then analyses the images and produces a radiology report to give to the doctor who ordered the scan.
Computerized tomography scans of the head are painless. Although scans themselves are usually quick (10-30 minutes), it is important to check with one’s doctor how much time the appointment will last, as some scans may take much longer than others, depending on factors like the reason for the scan and the level of detail the imaging needs to show. The process can be undergone as an outpatient.
In medical terms, a computerized tomography (CT) scan is used to create a series of pictures of the head and brain; imaging which can be used to visualize the internal organs, including blood vessels.
When is a CT scan of the head performed?
A computerized tomography scan of the head can be used to examine the bones of the face and skull, the sinuses and the brain, as well as the brain and its internal structures. Doctors can use radiology reports from the computerized tomography scan to accurately diagnose a wide range of conditions affecting the brain, skull and tissues of the head, oftentimes much earlier on in their course than would be possible by non-imaging means.
The cross-sectional/cut through pictures obtained via computerized tomography imaging can be used by a doctor in the planning of treatment for any suspected or detected conditions, such as strategizing a course of radiotherapy for brain cancer or determining where to take a biopsy (a procedure where a small piece of sample tissue is extracted using a needle from a very precise area of the head).
Symptoms which commonly require a CT imaging scan, for further exploration by a doctor, include:
- Difficulty speaking
- Difficulty swallowing
- Muscle weakness
- Numbness and/or tingling
- Vision impairment
- Vision loss
Symptoms and conditions which are commonly diagnosed or explored in further detail with the aid of a radiology report following a CT scan include:
- Severe headaches
- Abnormalities of the bones of the skull
- Atrophy (loss of nerve structures in the brain e.g. in Alzheimer's dementia)
- Infections (of facial or brain structures)
- Abnormalities of the blood vessels (arteriovenous malformations)
- Fluid buildup in the skull (hydrocephalus)
- Swelling of brain tissue
- Stroke, or the cause of a stroke
- Internal bleeding (hemorrhage)
- Brain aneurysm (a weak, bulging area in the wall of an artery in the brain which has the potential to rupture if left untreated)
- Benign brain tumours (non-cancerous growths)
- Malignant brain tumours (cancer)
- Birth defects
Before the scan starts, it is important to take off all removable metal objects, such as jewelry, removable mouth braces and dental bridges, because these can interfere with the quality of the CT images. It is often necessary to change into a loose gown for the procedure, and this will usually be provided by the doctor if needed.
People who feel very anxious or who may have difficulty staying still in the CT scanner (such as small children) may be offered a sedative before the procedure. Individuals are not required to avoid eating or drinking before a CT scan of the head, although this is often recommended for CT scans on other parts of the body.
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 ascertain 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, as well as anaphylactic (severe allergic) reactions and kidney damage. This is more common in people who have previously experienced kidney problems.
As opposed to 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 adversely to the contrast material.
During the 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, in order to contribute to the accuracy of the imaging process and help prevent blurry images.
Although the technologist operating the scanner will be in a separate room, one can communicate with them using an intercom system throughout the procedure. 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.
In a CT scan of the head, a customized head-holder may be used. This is a device which helps to keep the head immobilised and ensures that it remains in the same position throughout the procedure. In cases where a CT scan of the head is performed as part of emergency care (for example, to assess the possibility of internal trauma to the head or brain following an accident), a simplified pillow made of hard sponge may be used.
After the scan
The images produced during a CT scan depict cross-sections (slices) of the head. Following the scan, the images that are collected are processed by a computer. The radiologist will analyse 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 imaging scans are generally painless and non-invasive, 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 was 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 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 (head) FAQs
Q: What are the risks of undergoing a CT scan of the head?
A: CT scanning involves exposure to some X-ray radiation. Doctors generally agree that the risks are low compared to the potential risk of not being diagnosed with a dangerous health problem. The risk from a single scan is small, but it increases if an individual has many X-rays or CT scans over time. Newer imaging scanners can make it possible to encounter less exposure to radiation than older models.
Q: I am pregnant. Will undergoing a CT scan of the head affect my unborn child?
A: Although the risk of damage from radiation is usually considered insignificant in comparison to the benefits of performing the scan, it is advisable to tell the doctor if the person undergoing the scan is pregnant. They may be able to avoid exposing the unborn child to radiation completely by examining the head using other tests which do not involve such a high level of exposure to radiation, such as a head MRI scan or ultrasound.
Q: Can the head and neck be assessed during the same CT scan?
A: The head and neck can be assessed during the same procedure. It is particularly common after an accident for a CT scan or X-ray to be used to check for damage to the bones in the person's neck and head at the same time. If all possible conditions can be screened for using a CT scan, the head and neck will be assessed during the same procedure. Otherwise, the neck can be assessed separately, using whatever method of scanning is most appropriate to screen for the suspected condition(s).
Q: What is the difference between a CT scan of the head and a magnetic resonance imaging (MRI) scan? A: The principal difference between CT and MRI (magnetic resonance imaging) scanning 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.
A CT scan is more likely than an MRI scan to be used to investigate acute health issues as it is faster to perform. An MRI scan is more likely than an CT scan to be used for investigating soft tissue abnormalities.
For someone who has been prescribed a scan, there are several factors to consider; most importantly, what condition(s) or changes are being scanned for; in order to decide whether a CT scan or an MRI scan is the most suitable option. Based on an assessment of a person’s medical history and the diagnostic and/or imaging purpose of the scan, the doctor will decide whether CT or MRI scanning is suitable.
“Adverse Reactions to Contrast Material: Recognition, Prevention, and Treatment” American Family Physician. October 2002. ↩
“Effects of differences in head holder on image quality and radiation dose in head CT.” US National Library of Medicine, National Institutes of Public Health. October 2014. ↩