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Brain scan

Overview of brain scan

Have you experienced signs and symptoms of a neurological disorder? To confirm a diagnosis, your Dignity Health doctor may order a brain scan. A brain scan can refer to several different types of imaging tests.

Brain scans represent a way for your doctor to “see inside” your skull without having to do surgery. Our neurologists are experts at performing and reading brain scans. To learn more and get started, Find a Doctor today.

Why it’s necessary

As an imaging test, a brain scan can help your doctor evaluate structures within the brain. Some types of tests, like a positron emission tomography (PET) scan, can show how well your brain is functioning. Our neurologists use brain scans to help diagnose or monitor neurological diseases or disorders.

Brain scans are an excellent way to determine neurological diagnoses noninvasively. The information gained from a brain scan will help your doctor treat your neurological condition.

Your doctor will recommend a brain scan if he or she has reason to believe you may have a neurological condition or brain injury, or in order to rule out these conditions.

Common conditions treated with brain scans

Doctors are able to diagnose and monitor a variety of neurological conditions with brain scans, including:

  • Brain tumors or cysts
  • Blood vessel abnormalities
  • Multiple sclerosis
  • Stroke
  • Epilepsy or hydrocephalus
  • Head trauma including concussion>

Talk to your doctor if you have a neurological condition that may need to be monitored with a brain scan


There are three major types of brain scans: computed tomography (CT)magnetic resonance imaging (MRI), and positron emission tomography (PET). Within these categories, there are many other subtypes of brain scans that can measure oxygen usage in the brain, cerebral blood volume, and other aspects of brain structure or function.

CT scan of the brain

This test uses ionizing radiation (X-ray) to produce images of organs, tissues, and bones. CT scans are useful because they can show the area of the brain that is affected and can be used quickly to detect bleeding or clots. The procedure may be performed with or without the use of contrast dye, which is used to highlight different tissues in the brain. In either case, you will be asked to change into a hospital gown and lie on a special table that travels through the narrow opening of the imaging machine. If iodine-containing contrast dye is used, you will receive an intravenous (IV) line. The whole procedure lasts about 20 minutes.

CT scans are used to detect:

  • Tumors and cysts
  • Brain damage
  • Bone or vascular irregularities
  • Hydrocephalus (fluid buildup in the brain)

MRI brain scan

Unlike a CT scan, which uses ionizing radiation, MRI uses a magnetic field and radio waves to produce images. You will be asked to change and then lie on a table that moves through the magnetic resonance imaging machine. You cannot have any magnetic metal on or inside your body during an MRI. The most common type of contrast dye for brain MRI is gadolinium — if used, you will receive an IV line. For brain MRIs, a detector is also placed over the head.

MRIs are great for providing:

  • Detailed images of tissues
  • Blood flow measurements
  • Information on any mineral deposits
  • Diagnosis of stroke, multiple sclerosis, traumatic brain injury, tumors, infection, inflammation, and more

MRIs are painless and risk-free, though patients who are claustrophobic or obese may be uncomfortable during the procedure. Generally, MRIs take about an hour to complete.

Functional MRIs (fMRI) are used to obtain real-time images of blood flow in the brain. This is especially helpful to pinpoint areas that are active. They can also be used to localize brain areas of motor function, language, or sensation. They are helpful to study degenerative disorders as well.

PET scan of the brain

While CT and MRI scans look at the structure of the brain, a PET scan can show actual brain function. This test involves the injection of a radioactive tracer substance through an IV line in your hand or arm. This material takes about one hour to circulate through your system. After it does, you will lie on a table that slides through the scanning machine. The PET scan uses gamma rays.

PET scans show tumors and diseased tissue, blood flow, and can measure tissue metabolism. They are especially helpful in evaluating patients with epilepsy or memory disorders. PET scans can be used to diagnose cancer, as well as determine how you are responding to your cancer treatment.

PET scans last from 30 minutes to two hours. Some patients find it difficult to lie still for extended periods, while others experience anxiety and discomfort in the enclosed space of the scanning machine. Talk to your doctor or technician if you have claustrophobic tendencies, and about what steps can be taken to make the scan easier for you.


The risks for brain scans are generally low. CT and PET scans use radiation, but the amount of exposure is quite low and does not last long in your body.

There are heightened risks for pregnant women because fetuses are more sensitive to the effects of radiation. MRIs are a better option for pregnant women. If you are pregnant or think you may be pregnant, you should always discuss this with your doctor before undergoing a diagnostic scan or other procedure.

It is also possible to have an allergic reaction to the radioactive dye. This is very rare but can result in swelling, pain, or redness at the injection site.

The information contained in this article is meant for educational purposes only and should not replace advice from your healthcare provider.

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