brain scanning Flashcards
(10 cards)
What are the brain scanning techniques?
CAT scans (computerised axial tomography)
PET scans (positron emission tomography)
fMRI (functional magnetic resonance imaging)
What is a CAT scan?
• (Sometimes referred to as CT scans) – can be sued to take images of any part of the body including the brain.
• The person lies inside a large doughnut-shaped scanner and the scanner is slowly rotated around them.
• Involve passing X-rays into the head and multiple beams are passed around the head from different angles to gather more information.
• The information from the multiple X-ray beams is interpreted by a computer and a detailed image of the structure of the brain can be seen.
• Each image is a cross-section of the brain – when all the ‘slices’ are put together this can build up a very detailed picture.
• This is useful for detecting areas of the brain damage following an accident or the positioning of tumours in the brain BUT it does not give us any information about how the brain is functioning.
What are the strengths for a CAT scan?
CAT scans are useful for revealing abnormal structure in the brain such as tumours or structural damage. The quality of the images provided by CAT scans is much higher than traditional x-rays
Quick to conduct
Help surgeons better planner procedure before surgery takes place by being able to accurately see the layout of the brain structures - may make the procedure faster and more efficient
What are the weaknesses for a CAT scan?
CAT scans require more radiation the traditional x-rays, and the more detailed and complex the CAT scan is, the more radiation exposure the patient receives. This means that CAT scans can’t often be used.
CAT scans only provides structural information. Unlike other scans such as PET scans they do not give information about activity on the live brain they just produced still images. This means they have limited use and research linking brain areas to particular behaviours
What is a PET Scan?
• A form of nuclear medicine procedure as they involve injecting the patient with a small amount of radioactive material in order to conduct the scan.
• Patients having a PET scan of the brain will be injected with a substance ‘fluorodeoxyglucose’ (FDG) which is a tracer substance where the radioactive atom is attached to glucose because the brain will use up the glucose as a form of energy.
• Once the tracer has been absorbed into bloodstream, a task may be given to stimulate the brain and encourage activity.
• As the brain is working, the glucose will be used up and as this happens, the radioactive atoms start to break down emitting positrons.
• During this process gamma rays are produced and it is these that the scanner picks up.
• High concentration of gamma rays will be found in high areas of activity as a lot of glucose will have been used up there.
• The image produced from this information is in colour with areas of high activity shown by warmer colours like red and areas of low activity shown by cooler colours like blue.
• PET scans can be useful for investigating areas of the brain that are not functioning normally, which could indicate damage or tumours.
What are the strengths of a PET scan?
Pet scans show the brain in action, which is useful for psychological research as biological activity can be linked to behaviour
Pet scans indicate the specific areas of the brain that are involved in experience I do a localisation of function
What are the weaknesses of a PET scan?
Sometimes the results are not easy to interpret E.G pat scans on people doing the same task have shown different brain activity and different people. This makes it difficult to draw conclusions about which brain areas are linked to which behaviour
The precise location of active brain areas in relation to brain structure is difficult to pinpoint
Expensive to use
What is an fMRI scan?
• Enable images of brain activity to be gathered without the use of radiation.
• Brain activity is associated with blood flow in the brain and this activity is used to gather information by the scanner to produce a picture.
• Involves having your head placed inside a very large, very powerful electromagnet.
• Inside the magnetic field, the nuclei within hydrogen molecules in water align themselves with the direction of the magnetic field.
• As neural activity increases in the brain, blood flow increases in the active areas to keep up with the demand for oxygen. The oxygen is carried to the neurons in haemoglobin within red blood cells. Haemoglobin, when carrying oxygen, repels a magnetic field but when it has been deoxygenated, it will follow the direction of the magnetic field and it is these changes that the scanner will detect to create an image.
• The scanner send the information to a computer that is then able to create a map of activation to show changing levels of neural activity in different brain areas as tasks are being completed.
What are the strengths of an fMRI scan?
As with pet scans, FMRI shows important information about which areas of the brain are being used at one time
Non-invasive and do not involve injections
The images produced by FMRI are extremely clear and can show brain activity to the millimetre
What are the weaknesses of an fMRI scan?
Expensive to use
The technology is only effective as the person whose brain investigated stays perfectly still and this may be a problem for some people E.G children. This limits the use of FMRI.
There is around a five second timeline between brain activity in the image of pain on the screen which can cause problems when trying to interpret the information received
Because of the high-powered magnetic fields, some people are unable to have this kind of brain scan I.E people with a pacemaker or metal surgical implants
