PET and fMRI

Question	Answer
What did James 1890 hypothesis about MRI?	That an increased blood flow would cause the head to increase in weight therefore cause a seesaw to be displaced downwards.
Describe how PET works.	A radioactive isotope is injected in patient. Travels to the brain. The unstable isotope emits positrons which travel until they hit an electron causing release of gamma radiation at 180 degree angles to each other. This is then detected by the scanner and the difference in time the radiation hits indicates the position.
suggest why after the injection of an isotopic trace it will build up in areas of high metabolic activity.	Molecules such as oxygen or glucose are taken to metabolically active sites but due to their changed structure they can't be broken down and therefore just accumulate.
Give the isotopic trace used to detect tumors and why it is effective.	F(18)-DOPA. o Brain tumours have high neural amino acid uptake so we can see high levels of F(18)-DOPA in tutor cells.
Explain the subtractive scanning in relation to a PET scan, and give reasons why it is important.	We take a control scan with nothing going on then we when give an intervention we can subtract the normal background activity from the intervention scan. This will give us just the brain area which are being used for that task.
why can a PET scan be used to detect cancers?	cancers have higher metabolic rate to the surrounding tissue to take up more of the radioactive tracer injected.
How come we use L-DOPAs isotopic equivalent (F18-DOPA) instead of dopamine when doing PET scans?	dopamine cant cross the blood brain barrier so wont enter brain cells. L-DOPA is taken up by large neural amino acid transport system, and this crossing the blood brain barrier.
What happens to methamphetamine abusers dopamine transporters? what effect might this have one them?	They decrease. Result in slow motor reaction time, also potentially memory impairment.
What is the main use of MRI? How does this differ from fMRI?	To assess anatomical structure in the body. fMRI looks at the function of brain areas.
Describe how an MRI machine works	Strong uniform magnet alignes protons in our cells (H+ ions effectively protons). radio frequency coil then disrupts this orderd form by firing RW to specific areas of the body.  The RF coli is turned off, the protons stop resonating which releases energy, we measure this energy using the RF coil. A gradient magnet is then used to encode spatial information (piece the image back together)
Explain the importance of H+ and iron in MRI	there are differing amounts of H+ in different cells, therefore they all have different magnetic properties giving off different MRI signals. iron found in hemoglobin affects surrounding cells.
What is the actual signal we measure from an fMRI? Why does this give us information about neural activity?	Blood Oxygen Level Dependant signal (BOLD signal). Increased blood flow in associated with increased blood flow.
fMRI has a good spatial resolution, but what is this spatial resolution dependant on? Give problems with increasing this to extreme levels.	Magnet strength, normally ranging from 3T (tesla) up to about 7T. Going to very high magnetic fields the vestibular system can be activated.
Give a study which has shown fMRI combined with galvanic vestibular stimulation is a safe technique to use	lobel 1998
Give some applications of MRI	Clinical use to asses chances due to brain damage e.g. in a stroke or head trauma Sometimes used in basic neuroscience to assess learning/experience and how it affects the anatomy of the brain
Give a study which has used MRI to assess changes in brain structure as a result of learning.	Magurie 2000 looked at changed in the hippocampus in london taxi drivers after they had learned all the roads in london. Found they had larger hippocampus regions compared to normal people
What kind of fMRI is affected by blood oxygenation? What is deoxygenated blood associated with on an fMRI scan?	T2 scan, deoxygenation is associated with loss of signal and therefore darker patches on the scan.
Give a study which combined fMRI and MRI to look at difference in memory capacity. What did they find?	Maguire et al 2003, he looked at if memory champions have different brain structures to normal people. Study found no difference in IQ, no significant difference in brain structures (using MRI), they did find they used slightly different areas of the brain (fMRI) when memorising as they use different memorisation techniques such as “mental walk” or a “journey”
Suggest how you might go about looking at why when we tickle ourselves we feel it less, with regards to brain areas. Give the study which has already done this and what he found.	get someone to either tickle themselves or get someone else to tickle them. Look at differences the brain areas activated using fMRI. Blakemore et al,1998 Using fMRI they looked at activation of brain areas and found that cerebellum is linked with generating the counteracting signal reducing sensory input from self-generated actions

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	Created by alexlpeart over 10 years ago