FMRI Davind Norris
11 important questions on FMRI Davind Norris
What is paramagnetic, oxygenetad hemoglobin or deoxygenated hemoglobin?
What is the effect of deoxygenated hemoglobin on T2*?
Deoxy Hb distort surrounding magnetic field --> protons experience different magnetic field strangths --> protons precess at different frequencies --> more rapid decay in transverse magnetization --> shorter T2*
When is there more T2* signal?
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What contrast is shortened by the presence of deoxy-Hb, T2 or T2*
Which three parameters change upon activation and affect the amount of deoxy-Hb present?
- Oxygen consumtion.
- blood flow
- blood volume
What has the strongest effect on the levels of deoxy-Hb?
There is a net reduction in the amount of deoxy-Hb during activation.
What happens during activation to T2* and the MRI signal?
What determines the spatial resolution of fMRI?
What are three explanations for the post-stimulus undershoot?
- slow return of venous blood volume to baseline
- sustained elevated oxygen metabolsim.
- flow undershoot
flow undershoot is considered least likely. Sustained oxygen metabolism is favoured by many.
It's still not clear why there's an undershoot.
How is the temporal resolution defined?
How is the spatial resolution defined?
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