Brain scanning: CAT, PET and fMRI

CAT (CT) scans: structure

A CAT (or CT) scan uses X-rays taken from many angles to build cross-sectional pictures of the brain.

• Shows structure (anatomy), e.g. tumours, bleeding or damage.
• Fast and useful in emergencies.
• Uses radiation; cannot show brain activity.

PET scans: function

A PET scan involves injecting a small amount of a radioactive tracer (in Raine et al., a glucose tracer). Active brain areas use more glucose, so the scanner detects where the tracer collects.

• Shows function: which areas are active during a task.
• Raine et al. (1997) used PET while participants did a continuous performance task.
• Invasive (an injection), uses radioactive material, expensive, and timing is only to the nearest second or so.

fMRI scans: function

Functional magnetic resonance imaging (fMRI) uses a strong magnetic field to detect changes in blood oxygen. Active areas receive more oxygenated blood, which changes the magnetic signal.

• Shows function with good spatial detail (a few millimetres).
• Non-invasive and no radiation.
• Expensive; the blood flow signal is indirect and slightly delayed; participants must keep very still in a noisy, enclosed scanner, which lowers ecological validity.

Scans and aggression; evaluation

Scans can compare aggressive and non-aggressive groups or show which areas are active when people are provoked.

• Strengths: objective, scientific and replicable data; living brains can be studied.
• Weaknesses: findings are usually correlational; lab tasks in a scanner are artificial; small, specific samples (e.g. Raine's 41 murderers) limit generalisation.

Worked example

A researcher wants to see which brain areas become more active when people read insults. Which scan should they choose, and why?

1. They need brain activity (function), not just structure, so not CAT.
2. fMRI shows function without radiation or injection.
3. So fMRI is the better choice (PET would also show function but is invasive).

Answer: fMRI: it shows activity, is non-invasive and uses no radiation.

Check yourself

1. Which scan shows brain structure rather than activity?
   • CAT
   • PET
   • fMRI
   • EEG
   Show answer

   CAT. CAT uses X-rays to show anatomy.

2. Which scan requires an injection of a radioactive tracer?
   • CAT
   • fMRI
   • PET
   • EEG
   Show answer

   PET. PET detects a radioactive tracer.

3. What does fMRI detect?
   • Changes in blood oxygen
   • Radioactive glucose
   • X-ray absorption
   • Electrical activity on the scalp
   Show answer

   Changes in blood oxygen. fMRI tracks oxygenated blood flow.

4. Which scan did Raine et al. (1997) use?
   • CAT
   • fMRI
   • EEG
   • PET
   Show answer

   PET. Positron emission tomography, with a glucose tracer.

5. Why might scanning studies lack ecological validity?
   • Scans are subjective
   • Participants do artificial tasks lying still inside a scanner
   • Scans cannot be repeated
   • Scans only work on animals
   Show answer

   Participants do artificial tasks lying still inside a scanner. The setting and tasks are unlike real life.

6. Explain one advantage of fMRI compared with PET.
   Show answer

   fMRI is non-invasive and uses no radiation or injection, so it is safer and can be repeated, whereas PET needs a radioactive tracer.. Safety: no radiation.

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Sources

• Pearson Edexcel International Advanced Subsidiary/Advanced Level in Psychology specification, Issue 5 (February 2021)
• Pearson IAL Psychology component guide: WPS02 (Issue 2, November 2024)
• Simply Psychology: Neuroimaging, brain scanning techniques in psychology
• Pearson IAL Psychology summary of studies: WPS02

Last updated 8 November 2026. Spotted a mistake? Tell us.