brain scanning techniques

• CT: uses x-rays to produce a detailed image of slices of the brain, can be used to look for tumours, haemorrhages and any damage caused by stress.
• fMRI: magnet induces a magnetic field around the body to construct an image. Can be used to see structures of the brain (dead or alive), and to determine exactly where a tumour is so it can be surgically removed.
• PET: radioactive glucose tracer to show the brain activity, forms a 3D image of the brain and body
• Structural: can visualise anatomical properties of the brain and detect if there’s any damage by producing a cross-sectional image.  And deals with the diagnosis of intracranial disease such as tumours and injury.
• Functional: measures blood flow and neurone activity, shows the brain in activity. Deals with the diagnosis of metabolic diseases.
• [USE] A strength is that brain scans are an objective measure e.g., in Raines study he gathers information on glucose metabolism in the prefrontal cortex and the difference of it in murderers and non-murderers. This is a strength as it reduces experimenter bias as the results are not open to interpretation, there is factual information saying that the colour red on parts of the brain means it is active. This also increases the reliability of the findings as the colour red is not likely to be interpreted differently by other researchers.
• [USE] However, a weakness is that brain scans lack validity, they use tasks to recreate aggression which may not even produce aggression. Raine used a conscious cognitive performance task which lacks mundane realism. Getting participants to behave aggressively is not easy and very unethical as well as using brain scans in a study lacks ecological validity. Furthermore, aggravating participants presents ethical issues in protection of participants as they would feel extra stress than what they would be exposed to in everyday life.
• Positron emission tomography (PET) measures activity in the brain by tracking localised glucose usage. A person is injected with a small amount of radiotracer e.g., fluorodeoxyglucose, which binds to glucose in the blood. The brain areas most active will use more glucose, and the concentrated radiation from this region will be detected by the scanner. Positrons emit gamma rays when they collide with electrons in brain tissue. This then produces an image on a computer.
• + PET scans can be used for diagnosis of brain disease, most notably because diseases such as Alzheimer’s cause great changes in brain metabolism, which in turn causes easily detectable changes in PET scans.

  • PET scans have worse spatial resolution than fMRI scans when measuring brain activity. PET scans can measure changes in blood flow in the brain in an area of about 5-10 cubic millimetres, but fMRI can resolve down to 3 cubic millimetres.
• Functional magnetic resonance imaging (fMRI) uses radiofrequency energy and magnetic field to measure blood oxygen levels in the brain. The areas of the brain which are most active utilise the most oxygen. This “haemodynamic” usage of oxygen can be measured by the scan which forms a 3D image by detecting changes in magnetism (oxygenated blood will repel the magnetic field, whereas deoxygenated blood will follow the magnetic field). Produces high resolution images.
• + fMRI scans have better spatial resolution than PET scans when measuring brain activity. PET scans can measure changes in blood flow in the brain in an area of about 5-10 cubic millimetres, but fMRI can resolve down to 3 cubic millimetres.

  • fMRI scans only measure oxygen consumption, which is not a direct measure of brain activity, whereas PET scans directly measure the parts of the brain that are active because it focuses on glucose consumption.