08. RM Brain Scanning Techniques Flashcards
What are the 3 of brain scanning techniques?
- Computerised Axial Tomography (CAT)
- Positron Emission Tomography (PET)
- Functional Magnetic Resonance Imaging (fMRI)
Describe a CAT scan.
-Uses X-rays and a computer to create detailed structural images of the inside of the body, including the brain.
-The person lies inside a large doughnut shaped scanner and the scanner is slowly rotated around them. Images of the brain and body are taken from different angles.
-Each image is a cross section of the persons brain or body. When all the slices are out together this can build up a very detailed picture.
-Sometimes a dye is used to make the picture clearer, such as barium or iodine.
-Scan takes from a few minutes to 30 minutes. Pictures show how the area being scanned reacts to the X-ray, showing how far the X-ray is blocked, which could indicate a tumour or brain damage.
-CAT scanning can be used to examine damage to the brain.
What is a strength of CAT scans?
-CAT scans are useful for revealing abnormal structures in the brain such as tumours or structural damage.
-The quality of the images provided by the CAT scan is much higher than that of traditional X-rays.
What is a weakness of CAT scans?
-CAT scans requires more radiation that 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 cannot be used that often as receiving large amounts of radiation is harmful for the human body.
-CAT scans only provide structural information as unlike other scans, such as PET scans, they do not give information about activity of the ‘live’ brain, they just produce still images. This means they have a limited use in research linking brain areas to particular behaviours.
What is the procedure of CAT scans?
-Patient lies on a moving platform while being passed through the scanner. Or person lies still and scanner moves around them.
-Multiple beams are passed to the head by the X-ray.
Evaluate CAT/CT scans.
STRENGTHS
-Valuable in medicine to detect changes in physical structures to diagnose patients (good application).
-Is not painful and is non invasive.
WEAKNESSES.
-X rays can cause damage, eg cancer as patients are exposed to a years worth of radiation so they are used sparingly.
-Limited use in research as still images only provide structural information.
Describe a PET scan.
-Measures metabolic activity (ie areas that are most active) in the brain through blood flow.
-A person is injected with a small amount of radioactive substance through a vein in the arm such as glucose (the radiotracer). Brain areas which are most active will use more of it and so be detected by the scanner.
-This information is sent to a computer. Most active areas are coloured red or yellow and the least are represented as blue.
-It allows researchers to work out what parts of the brain are working at what time. The tracer contains small positively charged particles called positrons. It can be used to measure blood flow in the brain.
What is a strength of PET scans?
-PET scans show the brain in action, which is useful for psychological research.
-For example, Nora Volkow et al used PET scans to correlate the activity of dopamine transports during a cocaine-induced ‘high’ to a participants subjective experience of the drug. This means biological activity could be linked to behaviour.
-PET scans indicate the specific areas of the brain that are involved in experience, ie they provide evidence of localisation of function. For example, the person be asked to look at a picture, solve a jigsaw puzzle, or think about family holidays they went in as a child, and the linked brain area can be identified.
What is a weakness of PET scans?
-Sometimes the results are not easy to interpret. For example, PET scans on people doing the same task have shown different brain activity in different people. This makes it difficult to draw conclusions about which brain areas are linked to which behaviours.
-The precise location of active areas in relation to brain structure is difficult to pinpoint.
-There are ethical issues to do with the injection of radioactive glucose as used in PET scans.
-Radioactive substances cause damage to the tissues of the body, they may kill cells or cause mutations in the DNA code in cells. This means the technique can only be carried out once every 6 months with anyone one individual and some people may refuse to participate. This further limits the use of PET scans for psychological research.
What is the procedure of PET scans?
During a PET scan, radioactive material is injected into the veins of the patient. This material flows through the brain, and oxygen and glucose accumulate in active areas of the brain. The glucose is used in the active areas of the brain so the radioactive material breaks down giving off a neutron and a positron. The positron hit an electron and both are destroyed releasing gamma rays. Gamma ray detectors record areas where rays emitted which are displayed as images (‘hot spots’), showing areas of activity. This produces 3D detailed images of the brain PET scans can be used to see the effect that drugs have on the brain.
Evaluate PET scans.
STRENGTHS
-Shows the brain in action which is very useful for psychological research linking biological activity to behaviour.
-Indicate specific areas of the brain are involved in experience (it is useful for localisation of function).
WEAKNESSES
-Injecting the radioactive tracer is an invasive procedure and radiation can be harmful so there are ethical implications.
-It is difficult to isolate different brain functions specifically so we can’t be certain which part of the brain is performing which function (low validity).
Describe an fMRI scan.
-Uses radio waves to measure blood oxygen levels in the brain.
-Areas of the brain that are most active use more oxygen so more blood is directed to the active area (haemodynamic response).
-The activity is picked up through radio signals which produce a series of images if successive slices which are converted into a 3D image by a computer.
What is a strength of fMRI scans?
-As with PET scans, fMRI shows important information about which areas of the brain are being used at any one time.
-For example, Dustin Pardini et al used fMRI brain scans to measure the volume of participants amygdalas and relate thus to observed levels of aggression.
-Unlike PET and CAT scanning, fMRI does not use radiation and so it is a very safe method of studying the brain.
-The images produced by fMRI are extremely clear and can show brain activity to the millimetre.
What is a weakness of fMRI scans?
-Expensive to use.
-The technique is only effective if the person whose brain is being investigated stays perfectly still and thus may be a problem for some people, such as children. This limits the use of fMRI with some kinds of research.
-There is around a 5 second time lag between the brain activity and the image appearing on screen. This can cause problems when trying to interpret the information received.
What is the procedure of fMRI scans?
Uses radio waves to measure oxygen levels in the brain. It measures blood flow in the brain when a patient performs a task. fMRI works on the premise that neurons in the brain that are the most active during a task use the most energy.
