9.1.8.4 - Scanning

Question 1

How does a CT scan work? (4 points)

Answer 1

1. Multiple X-ray radiation beams are passed at different angles rotating around the head
   + Uses X-ray beams to view soft tissue - not just bones
   + The beams can be attenuated (reduced in strength) according to the density of the tissues in their path
2. A detailed cross-sectional image of the brain is produced by a computer

Question 2

What are the 4 advantages of CT scans?

Answer 2

Non-invasive and less harmful than PET scans

Identifies structures of the brain - lesions, brain damage, and tumours

Informs neurosurgeons of the location and layout of brain structures before attempting to access the skull

Can be used to monitor the progression of neurodegenerative disease (the loss of brain tissue over the course of an illness)

Question 3

What are the 4 disadvantages of CT scans?

Answer 3

Unethical to excessively expose people to X-ray radiation due to risk of cancer - can only be used a limited number of times

Does not provide information on brain activity (synaptic transmission)

Limited resolution - small structures in the brain cannot be distinguished

The patient needs to remain still - movement can cause the image to blur

Question 4

How does a fMRI scan work? (3 points)

Answer 4

Uses radio waves to measure the uptake of oxygen by the cells in different brain regions

Active areas of the brain have enhanced blood flow - they consume more oxygen (increased levels of oxyhemoglobin)

Active brain regions ‘light up’ on fMRI images when participants conduct cognitive tasks

Question 5

What are the 3 advantages of fMRI scans?

Answer 5

Non-invasive and more ethical - doesn’t involve injection of radioactive material like PET scans

Safer than CT scanning - no exposure to X-rays

Records:
+ Brain tissue
+ Anatomical structure
+ A map of activation showing information processing and blood flow in neurones

Question 6

What are the 3 disadvantages of fMRI scans?

Answer 6

Doesn’t provide information on how receptors function in synaptic neurotransmission

Not suitable for people with a cardiac pacemaker or metal surgical implant due to exposure to magnetic fields - can cause physical disruption to heart or organs

Claustrophobic patients may find the scanning machine unnerving - could lead to demand characteristics if it causes changes in brain activity

Question 7

How does a PET scan work? (4 points)

Answer 7

1. The patient is injected with a radioactive tracer (FDG fluorodeoxyglucose)
2. The tracer travels in the bloodstream to active regions of the brain as glucose is used up in respiration by neurone cells
3. As glucose is used up, the tracer breaks down, emitting positrons that radiate gamma rays
4. Gamma rays are detected by a scanner and active regions of the brain are identified

Question 8

What are the 3 advantages of PET scans?

Answer 8

Safer than CT scanning - no exposure to X-rays

A participant’s brain activity can be investigated when they are doing a cognitive task e.g. synaptic neurotransmission and receptors

Abnormal functioning of brain areas can be visualised - allows scientists to identify and predict the impact on patients

Question 9

What are the 3 disadvantages of PET scans?

Answer 9

Invasive procedure - involves the injection of radioactive glucose tracer

Duration of scan is 2-4 hours - can interrupt a person’s daily schedule/life

Can only be used once per year due to the danger of radioactive isotopes