Chapter 4: brain imaging

Question 1

Brain imaging STRUCTURAL techniques

Answer 1

MRI and CT are mainly structural techniques, they investigate the anatomy of the brain. They show WHERE something is happening.

Question 2

Brain imaging FUNCTIONAL techniques

Answer 2

PET, SPECT, EEG and MEG, ERP are mainly functional techniques, they investigate the underlying processes (like movement of water or blood). They show WHEN something is happening.

Question 3

Contrast agent

Answer 3

Other substance that enhances the contrast between different areas in the brain.

Question 4

Computerized Tomography (CT)

Answer 4

Using X-rays to visualise brain tissue in detail. Uses radiation and can identify:
- Atrophy
- Stroke
- Swelling of the brain
- Abnormalities in the brain

Pro’s: quick and available.
Con’s: harmful and not very detailed.

Question 5

MRI

Answer 5

Looks at proton movement.

Pro’s: detailed and less harmfull than CT.
Cons: expensive.

Question 6

T1 vs. T2 MRI

Answer 6

• T1: contrast between grey and white matter.
• T2: contrast between the tissue and the fluid.

Question 7

Diffusion-weighted imaging (DWI-MRI)

Answer 7

Looks at how the water moves in the brain. Can show:
- Isotropic diffusion: the water molecules move completely random.
- Anisotropic diffusion: the environment of the water molecules is restricted and the cells are densely packed.

Question 8

Functional MRI (fMRI)

Answer 8

Measures the acitivity of the brain by comparing blood flow to the active areas. Areas that are more active will have more blood flow and thus are more oxygenated, which causes a BOLD high signal.

fMRI is used to understand brain functions, but also to look at the important areas for a specific patient. When someone has to undergo brain surgery, the surgeons can use fMRI to determine where the vital functions in the brain are for this particular patient. It can also show where an epileptic seizure starts.

Question 9

Positron emission tomography (PET-scan)

Answer 9

Maps the functional processes of the brain. A radioactive fluid is injected into the patient and is used as a tracer.
Is used for:
- Plaques in Alzheimers.
- Disturbances in neurological disorders.

Pro’s: can detect brain disease before changes in brain anatomy can be seen.
Con’s: has a low discriminatory power.

Question 10

Single-proton emission computed tomography (SPECT)

Answer 10

A radioactive tracer in the blood is used in this technique.

Question 11

Electroecephalography (EEG)

Answer 11

Measures electrical signals with electrodes on the scalp.
These electrodes pick up the electrical activity of neurons in the cerebral cortex. This electrical activity is represented as brain waves with different frequencies, amplitudes and shapes.

EEG is used for:
- Diagnose of epilepsy or characterise epilepic activity.
- It can investigate sleep/wake disorders and provide information on the damage that was caused by a stroke or brain tumor.

Question 12

Event related potential (ERP)

Answer 12

A form of EEG where they pick out the waves right after a stimulus onset. This shows the activity in the brain as reaction to a single stimulus.

Question 13

Magnetoecephalography (MEG)

Answer 13

Measures a small magentic field that arised during electrical communication between neurons and it measures gamma waves that EEG connot measure. Gamma waves are present when someone is doing strong mental activities, like studying.

Question 14

Difference between MRI and EEG

Answer 14

MRI is good at showing WHERE something is happening and EEG at WHEN something is happening .