Brain Scanning Techniques Flashcards
What do PET scans measure?
- Measures metabolic activity in the brain i.e. the areas that are most active
Procedure of PET scans
- Radioactive tracer injected into bloodstream, tracer travels to active parts of body//brain.
- Person lays in PET scanner, which detects the radiation emitted.
- Once tracer absorbed, task to stimulate brain given.
How do PET scans produce images?
- Via the radioactive tracer emitting gamma rays, image then show areas of high activity
- Warmer colours like red show activity and cooler colours like blue show less.
Strengths of PET scans
- Produces valid (accurate) images of brain function (activity) objectively through measurement of gamma rays
- Replicable - the same procedure can be carried out in exactly the same way each time.
Weaknesses of PET scans
- Invasive due to injection of radioactive substance (low risk to health due to low levels).
- Low ecological validity: scans take place in an artificial setting and tasks to stimulate brain activity can be artificial, therefore do not measure true to life brain activity.
Procedure of fMRI scans
- Head is placed inside a large electromagnet.
- Once inside the magnetic field the nuclei within hydrogen molecules align themselves with the direction of the magnetic field.
- Increase in blood flow to deliver oxygen to active areas - Haemoglobin in blood repels a magnetic field when carrying oxygen, but when it is deoxygenated it follows the direction of the magnetic field
- These changes are picked up by the scanner to create an image.
Strengths of fMRI
- Safe: no risk to health due to radiation unlike CAT scans and non-invasive: no injection, unlike PET scans
- Valid because it is accurate and objective - shows structure AND function/activity of brain
- Replicable: the same procedure can be carried out in exactly the same way each time.
Weaknesses of FMRI
- Not suitable for all: if an individual has a cardiac pacemaker or surgical implants due to powerful magnetic field.
- Anyone who is claustrophobic or unnerved by loud noises and confined spaces may become quite distressed having to lie flat and still within the large tube.
- The brain is never at rest, especially if in a scanning machine, so it is hard to get a baseline measurement to compare to, this lowers validity when trying to pinpoint function of the brain of specific activities.
Procedure of CAT scans
- The person lies inside a large doughnut-shaped scanner and the scanner is slowly rotated around them, images of the brain (or body) are taken from different angles.
Results/images of CAT scans
- Each image is a cross-section of the person’s brain (or body), when all the ‘slices’ are put together this can build up a very detailed picture.
Strengths of CAT scans
- Valid, produces accurate, objective images of areas of brain damage but gives no info about how the brain is functioning (activity).
- Non-invasive/painless (no injection)
- Replicable: the same procedure can be carried out in exactly the same way each time.
Weakness of CAT scans
- Radiation poses a potential risk to health - pregnant women are not allowed to have a CAT scan in case of damage to the unborn baby.
- Doesn’t measure brain functioning (activity), only structure, so less detailed/ useful than fMRI or PET
Evaluation study tips
G - Can that scanning method be used with all individuals, or are there exceptions?
R - is the procedure standardised?
V - how much detail does the scan provide? What type of data is being produced?
E - does the scanning method produce any ethical issues?
Time/cost - how long does the scan take? Is it expensive? The costs of different scans vary because the cost of the price of the equipment, the time needed for the scan and the money required to keep the scanner running.
