What is a CT scan of the brain?

Computed tomography or CT scan brain test is an x-ray test used to obtain a detailed three-dimensional picture of the brain. The beams of x-rays produced by the scanner penetrate the brain at different levels, and the resulting images are picked up on the computer screen to form a three-dimensional picture of the brain. Sometimes, a dye (iodine) is administered with the test to increase the clarity of specific parts of the brain. The CT scan brain test is used to detect abnormalities in the brain and its surrounding tissue. Some variations in the scanning procedures such as CT arteriography and helical (spiral or volume-averaging) CT scan are used to detect disorders in blood circulation and provide accurate images of a specific area in the brain. The helical CT scan images the selected area of the brain in less than 30 seconds. This is helpful in children and patients who do not cooperate during the test.

  1. Who cannot have the brain CT scan done?
  2. Why is a Brain CT scan done?
  3. How should I prepare for the brain CT scan?
  4. What is the procedure for a CT scan of the brain?
  5. How does a brain CT scan feel?
  6. What do the results of the Brain CT Scan mean?
  7. What are the risks and benefits of the CT Scan Brain?
  8. What happens after the brain CT scan?
  9. What other tests can be done with the brain CT scan?
  10. Contrast vs on-contrast brain CT scan
  11. Doctors for CT Scan Brain

CT scan brain should not be carried out in individuals with:

  • Allergy to iodine.
  • Extreme fear and anxiety of closed or narrow spaces.
  • Pregnant women, unless it is essential. Women with regular monthly periods should undergo a brain CT scan during their periods or within 14 days of their period. This decreases the possibility of exposure of the fetus to the x-rays of the CT scan.
  • Frequent ups and downs or fluctuations in vital signs such as blood pressure, pulse, breathing and heartbeats.
  • Overweight or bodyweight more than 400 lbs or 181 kg.
  • Artificial implants in the body after hip replacement surgery, fillings used for dental cavities or those given a barium enema may give unclear images on the test.
  • Suffering from or at risk of developing kidney failure after exposure to the dye used in the test.

The doctor orders a CT scan brain test when symptoms indicate a problem in the brain or central nervous system, such as:

  • Sudden or continuous pain in the head or frequent changes in the pattern of headache
  • Seizures or epilepsy
  • Loss of sensation of touch or tingling
  • Decreased or complete loss of muscle power
  • Altered or double vision or loss of ability to see
  • Memory loss or difficulty in understanding
  • Muscle tightness or rigidity
  • Trembling in the hands or legs
  • Seizures
  • Difficult or unclear speech

You do not need any special preparations for the CT scan brain but do keep the following in mind:

  • If you are to have a brain CT scan with a contrast dye, your doctor will advise you to fast for four hours before the test. However, fasting is not required when the scan is done without contrast.
  • If you are on metformin, a diabetes medicine, you will be instructed to skip the dose of the medicine on the day of the test. You may continue to take the rest of your regular medicines before the test.
  • Drink a lot of water before the fasting period to prevent dehydration if you are fasting.
  • You will have to do a blood test for checking your blood urea nitrogen (BUN) and creatinine levels before the scan.

The laboratory technician will explain the test procedure to you when you go in for one. You may have to follow certain guidelines, such as the following:

  • Remove metallic items such as hairpins, clips, dentures, spectacles, jewellery and hearing aids before the test.
  • Sign the consent form that allows the laboratory personnel to perform the test procedure on you.
  • Change into a gown provided by the laboratory before going for the test.
  • You will be asked to lie on a narrow examination table and a contrast dye will be administered intravenously if required.
  • Pillows, straps, etc., are provided to support the head so that you remain still during the test.
  • An anti-anxiety medicine or a mild sedative may be given before the test if you are afraid or anxious.
  • The examination table slides into a circular or doughnut shaped scanning machine (gantry) that has x-ray tubes fixed inside.
  • The x-rays from these tubes scan your body while the scan machine rotates around your head.
  • You may be asked to hold your breath at some point during the procedure.
  • During this process, you may hear loud clicking or whirring sounds.
  • A CT scan brain without contrast is completed in one hour. The time taken doubles when the scan is done using the contrast dye.

It is essential to stay calm without making any movements during the test. You may feel discomfort while lying still for a long time if you have had an injury or a recent surgery. You may experience symptoms like nausea, a salty or metal-like taste in the mouth, mild headache, a sensation of heat in the body, etc if you are given a contrast dye. These symptoms disappear after some time.

Abnormal findings in the CT scan brain may indicate conditions such as:

Benefits of a brain CT scan are:

  • Harmful effects of radiation in different age groups, including elderly people and children are rare due to the minimal dose of radiation used in the test.
  • Reduces the need for exploratory surgery to reach a diagnosis.
  • Helps in deciding whether surgery is truly needed.
  • Helps diagnose and monitor the treatment of cancer.
  • Reduces the number of days of hospitalisation.
  • Helps in initiating quick treatment with rapid evaluation in conditions requiring intensive care and emergency conditions such as head injury, bleeding inside the brain, etc.

Risks of a brain CT scan are:

  • Exposure to CT scan radiations during pregnancy can lead to birth defects in the unborn baby.
  • CT scan radiation can be a high risk factor for nursing mothers and their breastfeeding infants.
  • Risk of an allergic reaction to the dye (iodine) injected during the scan.
  • Acute kidney failure due to allergy to the dye.
  • Increased risk of deep breathing, drop in blood pressure, nausea, vomiting and loss of appetite from lactic acidosis in individuals who are on metformin for the treatment of diabetes mellitus, when they are given a contrast dye for CT scan of the brain.
  • Sudden stopping of breathing for some time (apnea) after the test when an anaesthesia gas called xenon is used during the CT scan.

You will be asked to do the following after a CT scan of the brain:

  • If given a sedative, you will have to have a family member or friend drive you home.
  • Drink lots of water in order to flush out the dye from the body with urine.
  • Observe closely for 24 hours as you may develop an allergic reaction to the dye. You may notice symptoms such as a rash or hives on the skin, nausea, breathlessness or swelling of the parotid glands in the mouth (glands that secrete saliva) or even shock. There may also be redness, pain or swelling at the site of the intravenous injection. If you observe any such symptoms, contact your doctor or hospital immediately.

Sometimes magnetic resonance imaging (MRI) is done instead of a CT scan for observing other details and seeking more information about the abnormality in the brain. Positron emission tomography (PET) is another test that can be done for the diagnosis of brain disorders.

In some cases, to improve the clarity of certain regions in the brain, a contrast dye such as iodine may be used during the procedure, which will be administered intravenously. If a contrast dye is used, you will need to fast for four hours prior to the procedure. You may experience symptoms like nausea, a salty or metallic taste in the mouth, a feeling of heat in the body, a mild headache, etc, all of which will disappear over time. If the contrast dye is not administered, the scan takes about an hour. However, if the contrast dye is administered, it may take double the time. There may be a risk of allergy to the dye. Some other associated risks are a drop in blood pressure, nausea, loss of appetite, vomiting and acute kidney failure due to lactic acidosis in people who are taking metformin for diabetes mellitus. The scan should not be performed in individuals who are allergic to the contrast dye or are at risk of or are suffering from kidney failure.

After the test, to flush out the dye, a lot of water should be consumed. For the next 24 hours, check for symptoms of an allergic reaction to the contrast such as nausea, breathlessness, rashes or hives, swelling in the parotid glands or shock.

The contrast CT scan brain may be performed in a person with a history of infection, malignancy or tumour, whereas the contrast is not used in conditions such as trauma.

Dr. Rachita Gupta

Dr. Rachita Gupta

12 Years of Experience

Dr. Tejinder Kataria

Dr. Tejinder Kataria

35 Years of Experience

Dr. Shyam Singh Bisht

Dr. Shyam Singh Bisht

17 Years of Experience

Dr. Shikha Goyal

Dr. Shikha Goyal

18 Years of Experience

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