3.2.3 - brain scanning techniques Flashcards
what is a CAT scan?
a Computerised Axial Tomography scan
how do CAT scans work?
multiple x-ray beams are passed around the head from different angles
a computer interprets the information obtained from the beams
this allows a detailed image of the structure of the brain to be seen
what can CAT scans tell you about someone’s brain?
by seeing the structure of the brain you can look for areas of damage following an accident or identify the position of tumours
however, they don’t give information about the functioning of the brain
what are strengths of CAT scans?
quick, give accurate detail of brain structure so doctors can make decisions about treatment and surgeons can plan surgery in advance so patients aren’t under anaesthesia for so long which is less risky, image bone, soft tissue and blood vessels simultaneously
what are weaknesses of CAT scans?
involve exposure to radiation so should only be used if benefits outweigh risks, not recommended for pregnant women as the x-ray exposure could harm the unborn baby
what is a PET scan?
a Positron Emission Tomography scan
how do PET scans work?
patients are injected with a tracer substance called fluorodeoxyglucose (FDG)
the glucose has a radioactive atom attached to it and is used by the brain as energy - glucose and radio tracer go to more active brain areas
once the tracer is absorbed into the blood, a task may be given to encourage brain activity
as the brain uses the glucose, the radioactive atoms break down and emit positrons, and gamma rays are produced which a scanner detects
areas of high activity have more gamma rays as more glucose is used up and vice versa
a colour image is produced with warmer colours representing areas of high activity and cooler colours showing low activity
if using PET scans in research which requires more than one scan to be taken eg. to show activity in different tasks, why should there be 24 hours between each scan?
the radio tracer has to clear after the first scan or there may be carry-over from one task to the other
what can PET scans tell you about someone’s brain?
they indicate areas of the brain which aren’t functioning properly, possibly suggesting damage or a tumour
what are the strengths of PET scans?
indicate parts of brain showing abnormal activity, researchers can see where problems are and therefore predict the issues the patients may face, very useful to psychologists as they can compare brain activity between people doing different types of mental task
what are the weaknesses of PET scans?
more invasive, fairly low risk because small quantities of radioactive substance are used however patients still shouldn’t have too many, produces least detailed images
what is an fMRI scan?
Functional Magnetic Resonance Imaging scan
how do fMRI scans work?
the head is placed inside a large, powerful electromagnet
in the magnetic field, the nuclei in hydrogen molecules in water align themselves with the direction of the magnetic field
as neural activity increases, the demand for oxygen means blood flow increases in the active areas, and haemoglobin carries oxygen to the neurons
while carrying oxygen the haemoglobin repels the magnetic field (diamagnetic) but once deoxygenated it follows the direction of the magnetic field (paramagnetic)
a scanner detects these changes, creates an image and sends the information to a computer
what can fMRI scans tell you about someone’s brain?
a computer can create a map of activation which shows changing levels of neural activity in different parts of the brain while it completes tasks
(they are often used by psychologists to research brain activity)
what are the strengths of fMRI scans?
non-invasive, don’t require use of radioactive substances so generally safer than PET scans, produces most detailed images
