brain scans Flashcards
why are brain scans used?
different brain scans give different information, they can either look at biological aspects of an individual - e.g. diseases and tumours - and they can also look at physiological aspects - e.g. which area of the brain works for aggression or processing
what does CAT scan stand for?
computer axial tomography
(axial - x-rays are taken at lots of different angles)
do CAT scans look at brain structure or function?
brain structure - shows the physical anatomy of the brain, not the activity happening within it
what are CAT scans usually used for?
to diagnose conditions like stroke, head trauma, brain tumours and internal bleeding in the brain. they are also used to monitor and guide treatments for these conditions
how do CAT scans work?
it involves passing x-rays into the head, multiple beams are passed around the head from different angles. the information from the multiple x-ray beams is then interpreted by a computer and a detailed 3D image of the brain is created (which is made up of the multiple 2D slices from all the x-rays)
who can’t have a CAT scan?
pregnant women (it’s possible that exposure to x-rays can cause damage to new-born babies)
what is sometimes used to improve image quality?
contrast dyes, e.g. iodine and barium usually make the images clearer
what will a patient experience with a CAT scan?
the scanner is a donut shaped platform and the patient must lie still while the scanner moved around. it usually lasts for about 30mins and a dye may sometimes be used
when were CAT scans created?
they were developed in the early 70’s
what does PET scan stand for?
positron emission tomography
are PET scans used to look at brain function or structure?
brain function/activity - they show which parts of the brain have abnormal activity, which can help researchers with identifying any possible existing problems
what are PET scans usually used for?
can help with identifying a variety of conditions, e.g. epilepsy, brain disorders, depression, if both sides of the brain are being used equally, etc
how does a PET scan work?
patients are injected with a tracer and, once it has been absorbed into the bloodstream, a CPT task may be given to stimulate the brain and encourage activity. gamma rays are produced and show which areas have high/low activity depending on the glucose level they pick up. high concentration of gamma rays will be found in areas of high activity as a lot of glucose will have been used up there
who can’t have a PET scan?
pregnant women - risks involved with radiation
what are patients injected with for PET scans?
a radioactive tracer (e.g. FDG) - its injected into a vein, usually in the patients arm or hand and then you have to wait 45mins for it to be fully absorbed into their body. this helps to measure glucose metabolism (how much glucose is used in each brain area)
what does a PET scan look like?
appears as multicoloured images of the brain. areas of high activity are usually warmer colours - e.g. red - and areas of low activity are cooler colours - e.g. blue
what will a patient experience with a PET scan?
patients will have restrictions on what they can eat/drink beforehand - they’re usually told not to have anything. the scan is invasive and takes around 45mins.
when were PET scans created?
they were developed in the late 70’s
what does fMRI scan stand for
functional magnetic resonance imaging
do fMRI scans look at brain structure or function?
they look at both the structure and function of the brain
what is an fMRI scan usually used for?
usually used to look at tumours, assessing the impact of brain injuries, to monitor the effectiveness of treatments and also to investigate cognitive processes
how does an fMRI scan work?
patients are put inside a powerful electromagnet. as neutral activity increases in the brain, blood flow also increases in active areas in order to keep up with the demand for oxygen. oxygen haemoglobin repels the magnetic field and, once its deoxygenated, it follows the direction of the magnetic field and the scanner detects these changes and creates an image
who can’t have an fMRI scan?
anyone with a cardiac pacemaker, people with metal surgical implants - because of the use of high-powered magnetic fields
why might fMRI scans not be suitable for all patients?
anyone who is claustrophobic or unnerved by confined spaces/loud noises nay becomes stressed during the scan as they have to lie flat and very still for the duration of it (fMRI scans are highly affected by movement)
what does an fMRI scan image look like?
they use a colour coding system to represent different activity to make it ore easily interpretable
what will a patient experience during an fMRI scan?
it will make a loud noise, they will need to remain very still and they usually last for up to 55mins
(fMRI scans were developed in the 1990’s and are a relatively new procedure)
CAT scan study
Lusins et al - 50 alcoholic patients, during the scan they were alcohol and drug free, 58% of them were found to have had cerebral atrophy which affects brain size and loss of neutrons and connections. however, the only significant factor was due to the duration of the drinking problem
PET scan study
Rain et al (1997) - scanned murderers brains who pleaded NGRI and compared them to non-murderers. given FDG tracer and completed a CPT. significant differences were found for activity in the pre frontal cortex (lower glucose metabolism)
fMRI scan study
Li et al - used a matches pairs design of 14 male ex heroin addicts and controls. exposed to 24 pictures of drug related activity and 24 neutral pictures. there was a significant difference in activation in regions associated with the reward system and parts of the PCC
evaluation of CAT scans (+)
- a CAT scan is good for detecting changes in physical structure and so they are valuable when looking at things like tumours and haemorrhages. this can help with planning surgeries. produces a detailed 3D image
- they are very detailed and provide a slice by slice structure of the brain which means they are more likely to accurately detect brain abnormalities and help with identifying an accurate layout of the brain for surgery
evaluation of CAT scans (-)
- they can be seen as ethical as patients are put at risk due to being exposed to radiation, which could cause issues such as cancer if they are exposed to too much. one x-ray is equivalent to the amount of radiation you would naturally be exposed to in 1-3 years. therefore, they should only be used when completely necessary which makes for poor reliability as they shouldn’t be unnecessarily repeated
- they are impacted by movement. may distress patient with claustrophobia/who struggle with small spaces. can also lead to results being messed up if movement occurs or having to be re done which means more exposure to the radiation
evaluation of PET scans (+)
- highly valid in measuring what it claims to measure, they can be more sensitive to pic up levels of brain activity and showing high and low levels of activity in the brain with each scan. this shows the accuracy as each scan can be compared due to it being objective
evaluation of PET scans (-)
- difficult to interpret due to it being difficult to irate rain functioning precisely due to so many areas of the brain being active at once. this can decrease the validity as it cab make it harder to determine direct cases of human behaviour from a PET scan.
also because of low spatial resolution (4-5mm vs CAT scan 0.3-0.6mm) which can lead to incorrect conclusions and therefore decreases validity - invasive procedure, tracer injected
evaluation of fMRI scans (+)
- newer technology (developed in the 90’s) and are therefore more advanced and detailed. this is likely to increase the validity of the results. looks at both structure and function, more in depth
- no radiation involved as it uses electromagnets, patient is exposed to less risks which makes this scan more ethical as harm is less likely to occur
evaluation of fMRI scans (-)
- they are extremely affected by movement so patients have to stay very still. those who struggle with small spaces and/or loud lines may become distressed and struggle to regain completely still during the scan due to this. this shows practical issues
- thee is slow temporal resolution (1-4secs in comparison to CAT 80ms), which means that its harder to accurately predict when brain activity starts due to how long it takes to get the image
