A computed tomography (CT) scan of the head is an imaging scan that uses X-rays to develop a 3D image of the skull, brain, and other related areas of the head.

A CT scan of the head can provide more detail than a traditional X-ray, which is particularly useful when a doctor wants to check the blood vessels and soft tissues in the body.

In this article, we explain why a doctor may order a CT scan of the head and what a person can expect if they need to undergo this procedure.

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A person may have a CT head scan after trauma to check for damage.

A doctor may use a CT head scan to get images in an emergency, to make a medical diagnosis, or to see how well treatments are working.

Some of the reasons why a doctor may order a head CT scan include:

  • looking for possible damage after trauma to the head, such as soft tissue injuries, brain bleeding, and bone injuries
  • assessing a person having stroke-like symptoms to see whether there are signs of a blood clot or brain bleeding
  • looking for a possible brain tumor or other brain abnormality
  • checking the effectiveness of medical treatments in shrinking a brain tumor
  • assessing birth conditions that cause the skull to form abnormally
  • evaluating a person with a history of hydrocephalus, a condition in which an accumulation of cerebrospinal fluid causes the enlargement of the brain ventricles

If a person is having brain-related symptoms, such as changes in personality or affected movement, a doctor may order a head CT scan to make sure that a brain abnormality is not the underlying cause.

A doctor should provide specific instructions for the day of the CT scan. These will include whether or not to refrain from eating or drinking for a certain period before the scan.

The doctor will also usually ask the person to take off any jewelry, removable dental work, or hairpins because these can affect the scan's images.

Sometimes, people who take metformin (Glucophage) may need to refrain from using it for a few days before getting a CT scan with contrast dye. The combination of this drug and the dye can cause a severe reaction in some individuals.

Contrast dye is a substance that the person may receive by injection before a scan. It makes certain areas of the body show up more easily on a scan. However, not all CT scans require contrast dye.

The person will often complete a checklist before undergoing the scan. The checklist includes a medical history of conditions that can affect a person's health, such as kidney disease, heart disease, asthma, and thyroid problems. Some health issues may affect a person's ability to receive intravenous (IV) contrast.

The scanner usually looks like a circle shaped machine that has a hole in its center. In the center, there is a bed on which a person lies during the procedure. The scanner is usually open, which helps the person feel less claustrophobic.

A radiology technician may ask the person to change into a gown before going into the room with the CT scanner.

Before the scan, a radiology technician may put an IV line in place, usually in the person's arm, if the scan uses contrast dye.

During the scan, the radiology technician will talk to the person via a speaker to let them know them when the scan is starting. The scanner will direct X-ray beams at the person's head. The X-rays will come back to the scanner, transmitting the images back to a computer.

After the initial scan, the radiology technician may deliver the IV contrast material. They will then restart the CT scan. The technologist will review the images to ensure that they are of high quality and are free of blurring in any key areas.

The average CT scan of the head takes no more than 10 minutes.

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Children are sensitive to radiation, so a doctor may only order a CT scan when necessary to confirm a diagnosis.

Doctors may order a CT head scan if a child has experienced a recent injury or has a medical history of skull or brain abnormalities.

As a CT scan is relatively quick, many children can stay still long enough for the technician to complete the scan. However, if a child cannot remain still for the scan — as is the case for babies — it may be necessary to perform the procedure with the child under anesthesia.

Children are typically more sensitive to radiation than adults. As a result, doctors tend to reserve CT scans for when they are necessary to make a diagnosis. A radiology technician can usually adjust the settings on a CT scanner to deliver the lowest possible dose of radiation.

The CT scan is a painless, noninvasive procedure, and doctors generally consider it to be safe. However, it carries some possible risks.

As a CT scan exposes a person to radiation, there is a risk that the person could develop cancer from excessive radiation doses. However, the risks for this after one CT head scan are minimal. A person can ask their doctor if they should be concerned about the radiation dose from a CT head scan.

Doctors will usually recommend that women avoid CT scans during pregnancy. However, as one CT scan is unlikely to pose a significant risk, a doctor can offer advice on whether the benefits outweigh the risks.

Read about the safety of X-rays here.

A CT scan can be noisy. Sometimes, this noise or the fear of being in an enclosed space can provoke anxiety in a person. For this reason, doctors may sometimes give a person sedating medicines before they go into the CT scanner.

If a person receives a contrast dye during the procedure, they could be at risk of experiencing an allergic reaction to the dye.

Contrast dye can also cause other symptoms that may be temporarily unpleasant but are not an allergic reaction. These may include a warm feeling throughout the body, a burning sensation, or a metallic taste in the mouth. Sometimes, a doctor may prescribe a steroid or advise a person to take diphenhydramine (Benadryl) before undergoing the scan.

A medical specialist called a radiologist will examine the imaging scans, looking for any abnormalities in the brain and surrounding tissues. They will write a report of their findings and send it to the doctor who ordered the scan.

If a person is in the hospital and undergoing the scan as an emergency, the radiologist will report any immediately concerning results as quickly as possible.

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A person's doctor can advise on which type of scan is best to diagnose a certain condition.

Sometimes, a doctor may recommend both a CT scan and an MRI scan of the head. An MRI scan does not expose a person to radiation. Instead, the device uses a magnetic field to generate images of the body's soft tissues.

While a CT scan is helpful in displaying some aspects of the head and brain, an MRI scan sometimes has higher sensitivity. As a result, it may be more effective in revealing disease processes in the brain and inflammation in the membranes covering the brain, which are known as the meninges.

Doctors will consider the advantages of each type of scan for scanning the head. The benefits of a CT scan compared with an MRI scan include:

  • A CT scan is faster than an MRI scan, so doctors usually use it for emergencies.
  • A CT scan generally costs less than an MRI scan.
  • Doctors can perform a CT scan on a person who has metal devices, such as a pacemaker, nerve stimulator, or cochlear implant. A person with these devices cannot undergo an MRI because of the magnet's attraction to metal.

The benefits of an MRI scan compared with a CT scan include:

  • An MRI does not involve radiation exposure, making it preferable for children who may require multiple scans.
  • MRI scans can show soft tissues and structures that bone may hide in a CT scan.
  • A person requires a smaller amount of IV contrast for an MRI scan than for a CT scan.

People can talk to their doctor to evaluate the aspects of each scan and determine which is most appropriate for them.

A CT scan of the head is useful for helping a doctor assess damage after an accident or head trauma. It also allows them to look for brain abnormalities, such as tumors and skull defects.

Doctors consider CT scans to be relatively safe and noninvasive procedures, even though they involve exposure to radiation. People can discuss any possible risks with their doctor.