Health and Stroke

What is an EEG? What Can it Show that an MRI Cannot?

Learn more about what an EEG is

Dec 12, 2022

Zeit Medical

What is electroencephalography, or EEG? In this blog post, we will discuss the differences between EEGs and magnetic resonance imaging (MRI) scans. Additionally, we will explain why EEGs are such an important tool for researchers and clinicians when it comes to brain health.

What is an EEG?

EEGs are used to measure small electrical currents, so called "brain waves," that are part of the brain’s natural physiology in real-time. The brain’s electrical activity is sometimes compared to a large orchestra where there is continuous musical communication between the different musicians and all musicians contribute to an ocean of different waveforms.  Obtaining an EEG typically involves a series of electrodes to pick up said brain waves at certain points on a patient’s head. The brain waves can provide real time information about the level of activity and consciousness. As such, EEG can be used to show problems with the way the brain is working, and it can help diagnose conditions like epilepsy and dementia. EEG is the only tool that provides continuous feedback on the brain’s activity level.

Types of EEG

Four primary types of EEG can be utilized. These include:

  • Ambulatory EEG. This type of EEG is worn on the head like a headset and can be used to record brain activity over long periods while the patient goes about their normal day.
  • Routine EEG. This type of EEG is the most typical use of an EEG in a clinical or hospital setting to get a relatively quick look at brain waves in 20 minutes. The doctor may ask specific questions or try to alter the patient’s brain state with light or breathing to further assess brain health.
  • Prolonged EEG.  This type of EEG is used when doctors want to get a long-term recording of brain activity, from a few hours to even days. This may be done in cases where there are concerns about seizures, epilepsy, or other major changes in cognition.
  • Sleep EEG.  This type of EEG is used to track brain waves and is the gold standard when it comes to sleep depth. This is used in helping diagnose different sleep disorders. .

EEG and Stroke

When it comes to stroke management, EEG can play a pivotal role in both prevention and management. This is because an EEG can be used to show changes in the brain that may happen before a stroke, helping doctors take steps to prevent a stroke from happening. EEG can also show what areas of the brain are affected by a stroke and how well those areas are recovering. Additionally, an EEG can be used during brain surgery or to look at the brain activity of a patient in a coma.    

How Does an EEG Compare to an MRI?

MRI scans are very popular and are often used to diagnose many different medical conditions. However, they do not provide real-time physiological data as EEGs do. Thus, an MRI can only provide information about structures and tissues at one point in time. An EEG is most often used when a doctor wants to see how the brain is functioning in real-time. This may be done when a person is having problems such as seizures, dementia, or epilepsy. It can also be useful for studying sleep and changes in cognition.

Utilizing EEG to Get Answers

EEGs offer a lot of unique information about the brain that MRI scans cannot provide. They are an important tool for diagnosing and managing conditions like stroke, epilepsy, and dementia. In fact, cutting-edge EEG technology is being designed to monitor brain activity changes at night that can alert an individual to the onset of a stroke and get them treatment significantly sooner.  If you have questions about your brain health, talk to your doctor about whether an EEG might be right for you.

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