Unit 4 - Brain scans

What is a CAT (CT) scan?

This is a structural brain scan where x-rays determine the rate of absorption in different areas of the brain.

How are CAT (CT) scans conducted?

Before x-rays are taken, radioactive dye is injected into patients before entering the cylindrical tube. A series of x-ray beams are passed through the head, creating cross-sectional images of the brain. They combine this set of x-rays to form 2D or 3D images of the area being scanned.

What are the strengths of CAT (CT) scans?

• Produce high quality images, better than produced by x-rays alone.

• Can reveal structures in the brain that appear abnormal (e.g. tumours).

What are the weaknesses of CAT (CT) scans?

• Only provide researchers with structure of the brain, not the electrical activity of the brain.

• Exposure to radiation - the more detailed the scan needs to be, the more radiation an individual is exposed to.

What are PET scans?

This is a structural brain scan where radioactive substance binds to glucose and when used up, the radioactive tracer is left in active areas of the brain. This is later detected by a scanner.

What is the procedure for a PET scan?

Patients are given a radioactive tracer (e.g. FDG). Areas of the brain that are more active will require the most glucose during the cognitive test, so the tracer will be temporarily left behind. After the task, detectors in the scanner can highlight the most active areas, allowing an in-depth image of brain activity.

What are the strengths of PET scans?

• Allow researchers to see chemical activity in the brain. As a result, they can distinguish between benign and malignant tumours.

• Useful for psychological research as they look at more active brain areas.

What are the weaknesses of PET scans?

• Costly to run and maintain - limited availability for research

• Not as precise as scans such as the MRI

• Radioactive dye needed - this must be administered

What is an EEG scan?

A functional brain scan that measures electrical activity across the brain.

What is the procedure for an EEG scan?

They record electrical activity of the brain through electrodes placed on the scalp. They detect tiny electrical charges resulting from activity of brain cells. They measure different types of brainwaves. These are amplified and displayed as graphs.

What are the strengths of an EEG scan?

• Non-invasive - does not involve radiation or inserting instruments

• Temporal resolution - readings taken every millisecond - changes can be observed in real-time.

What are the weaknesses of an EEG scan?

• Poor spatial resolution - only detects information in superficial regions of the brain rather than deeper areas.

• Patient discomfort - could result in unrepresentative readings 

What is an MRI scan?

This is a structural brain scan that monitors radio signals emitted by water molecules.

What is the procedure for an MRI scan?

They use magnetic fields and radio waves to create detailed images of the brain’s anatomy and activity. There is no radiation involved. They involve lying in a long tube, typically lasting 30-60 minutes. They are used for identifying brain tumours, strokes and more.

What are the strengths of MRI scans?

• Non invasive - no radiation or surgery required

• Detailed images - high resolution

• Objective measures - used to identify brain abnormalities.

What are the weaknesses of MRI scans?

• Poor spatial resolution - limits ability to identify detailed brain regions and circuits.

• Poor temporal resolution - slower than EEGs and cannot accurately detect onset of brain activity.

• Causation - they do  not provide a direct measure of neural activity making it difficult to determine which brain region is associated with a particular function. 

What is an fMRI scan?

A functional brain scan that monitors the flow of oxygenated and deoxygenated blood to show which areas of the brain are active (using oxygen). This shows real-time brain activity. 

What is the procedure of an fMRI scan?

They measure changes in blood flow in the brain when a person performs a task. They operate on the principle of Blood Oxygen Level Dependent (BOLD) where changes in neural activity affect blood level, leading to a higher demand for oxygen. This allows researchers to map brain activity in real-time.

What are the strengths of an fMRI scan?

• Non invasive - no radiation and virtually risk-free.

• High spatial resolution - allows psychologists to discriminate different brain regions with greater accuracy.

• Clear visualisation of brain activity - creates 3D images.

• Good spatial recognition.

What are the weaknesses of an fMRI scan?

• Poor temporal resolution - difficult to capture rapid neural events

• Costly

• Subjective interpretation