Brain Imaging Techniques : CT Scan, MRI, fMRI, PET Scan


Broadly speaking, we all agree that mental health and physical health are interlinked. There is increased incidence in those having chronic medical illnesses to have mental illness. Similarly mentally ill are at increased risk of developing medical illnesses. Brain Imaging Techniques help in diagnosing and predicting behavior connected to physical health.

By this time, we already know the broader causes for mental illness. Mental illness has biological, psychological and social components in its aetiology.

According to this, every mental illness has underlying biological changes in body but these can be too miniscule and too non-specific to detect, In fact, even attribute as causing the mental illness in routine physical tests in clinical practice. Such mental illnesses are called as functional just to differentiate them from organic, or substance induced.

These Brain Imaging Techniques are useful to examine the brain damage, brain disease, and severe mental illness.

  • Electroencephalography (EEG)– shows brain activity
  • Positron emission tomography (PET) scans -shows where neurons are firing.
  • Magnetic resonance imaging (MRI) – shows grey matter, white matter, and cerebrospinal fluid.
  • Functional magnetic resonance imaging (fMRI) scans 
  • Computerized Tomography (CT scan) – Repeated X-ray of brain to produce 2D image
  • Neuropsychological Assessment Battery® (NAB®) by Robert A. Stern, and Travis White, to Assesses a wide range of cognitive skills and functions Age range:18- 97 years; Time:3 hrs & 40 minutes for all five modules.

CT Scan – Computerized Tomography

Computerized Tomography of brain is nothing but X-ray of the head taken repeatedly and constructed by computer to give two dimensional images of the head.

Hence, there is risk of radiation exposure as it happens in case of taking chest-x-ray. It is less costly, less time consuming and available in most cities when compared to MRI brain.

This helps in identifying trauma to skull bones that cover the brain, any space occupying lesions like tumours, blood or any abnormal calcium deposits in the brain matter.

Usually, any trauma that leads to fracture of the skull bone also leads to damage to underlying brain. Whenever there is a blow to head, follows the sudden onset altered sensorium. Some specific neurological abnormalities along with severe headache in person with known hypertension may be candidate for CT brain.

Magnetic Resonance Imaging

Like many other Brain Imaging Techniques, this much advanced technique does not involve radiation. Takes longer time to scan the brain and to get brain image person has to lie down calm in big machine.

It is sometimes very frightening for even healthy persons. This machine operates in artificially created strong magnetic field, it is usually kept in a room separated from other areas.

Persons before entering the machine should make sure that they do not have any kind of metal with them or inside their body. For example, artificial cardiac pacemakers, metallic bone nails or fixatives.

Some suspicious findings in CT scan of the head can be more clearly identified in MRI brain. In addition, MRI brain helps in identifying abnormalities of nerve fibres, locating abnormalities to specific areas of the brain are much better.

Another advantage is visualizing blood vessels using contrast materials to enhance their appearance. Moreover, visualizing spinal cord, as it is difficult to be see in CT scan due to bones covering the entire spinal cord.

fMRI – Functional MRI

Functional magnetic resonance imaging is based on comparing brain images during cognitive activity.

However, fMRIs do not use radioactive material. More specifically, functional magnetic resonance imaging (fMRI) is based on the principle that oxygen-rich blood is an index of brain activity. The research participant reclines with
his or her head surrounded by a large, doughnut-shaped magnet.

This magnetic field produces changes in the oxygen atoms. A scanning device takes a ‘‘photo’’ of these oxygen atoms while the participant performs a cognitive task.

For example, researchers have used the fMRI method to examine regions of the brain that process visual information. They found that specific locations in the brain respond more to letters than to numbers.

In general, an fMRI is preferable to a PET scan because it is less invasive, with no injections and no
radioactive material. In addition, an fMRI can measure brain activity that occurs fairly quickly—in about 1 second.

The fMRI technique is more precise than a PET scan in identifying the exact time sequence of cognitive tasks. The fMRI technique can also detect subtle differences in the way that the brain processes language.

For example, certain researchers used this technique to discover a different pattern of brain activation when
students read sentences like, ‘‘The young child played in a backyard,’’ as opposed to
‘‘A young child played in a backyard.’’

Notice the subtle difference in meaning between ‘‘A child’’ and ‘‘The child.’’ Would you have thought that your brain responded differently to these almost identical phrases?

PET Scan – Positron Emission Tomography

When you perform a cognitive task, your brain needs chemicals such as oxygen to support the neural activity. The brain does not store oxygen. Instead, the blood flow increases in the activated part of the brain in order to carry oxygen to that site.

Brain imaging techniques measure brain activity indirectly. These techniques are based on
the following logic: By measuring certain properties of the blood in different regions of the brain while people perform a cognitive task, we can determine which brain regions are responsible for that cognitive task.(Coren et al., 2004; Szpunar, 2010).

In a Positron Emission Tomography (PET scan), researchers measure blood flow in the brain by injecting the participant with a low dose of a radioactive chemical just before this person works on a cognitive task. This chemical travels through the bloodstream to the parts of the brain that are activated during the tasks.

While the person works on the task, a special camera makes an image of the accumulated radioactive chemical in various regions of the brain. For example, the participant might perform two slightly different cognitive tasks.

By comparing the two brain images, researchers can determine which parts of the brain are activated when the participant works on each task.

PET scans can be used to study such cognitive processes as attention, memory, and language. They require several seconds to produce data, so this method is not very  precise. If the activity in a specific brain region increases and then decreases within this brief period, the PET scan will record an average of this activity level.

Furthermore, in the current era, PET scans are used less often than some other imaging techniques, because they are expensive and they expose people to radioactive chemicals.

Electroencephalogram (EEG)

EEG is a recording of a summed up electrical activity of the superficial layers of the brain. It is useful in cases of clinical suspicion of epilepsy either generalized or partial complex epilepsy.

EEG helps in identifying abnormality and sometimes localizing part of the brain from which abnormal activity is coming. When person is not having active convulsions, still there can be abnormal electrical activity. Thus, this technique records it, which helps in the diagnosis of seizure.

The procedure is placing electrical activity recording conductors over specific areas of the head. It can record during awake state and during sleep. Patient has to be co-operative for this test.

Recorded activity needs specially trained person to read it and interpret it. Detection of some deep seated abnormal activity of the brain is difficult. Video-EEG is an advanced version of this where an expert continuously monitors a person’s brain electrical activity in a room along with video recording of the person.

EEG is also used in evaluating sleep disorders.


  • Anderson, J. R. (2015). Cognitive psychology and its implications. New York: Worth Publishers
  • Galloti, K. M. (2004). Cognitive psychology in and out of the laboratory. USA: Thomson Wadsworth.
  • Matlin, M. (1994). Cognition. Bangalore: Harcourt Brace Pub.

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