fMRI Flashcards
Explain how activity in the brain works (biologically)
Trigger causes region of brain to respond.
Causes increase in metabolism and oxygen consumption in that area.
Increase in blood flow provides large oxygen gradient to deliver oxygen rapidly.
more brain activity = more local blood oxygenation
How does BOLD work - Blood oxygen level dependant mechanism
Oxygenatef blood is diamagnetic similar to tissues
Deoxygenated blood is paramagnetic comparetively
Differences in mag sucesptability in cells and tissues create local field gradients inside and around vessels.
Causing spins to process at different freq and dephase causing T2* decay
% oxygen saturation of Hb eqn.
max number of O2 bonded to Hb
Number of O2 bounded to Hb
Max 4
What is saturation dependant on
Partial pressure of O2.
O2 rich areas( eg lung) release 02 to areas with high metabolic activity causing local oxygen depletion
When Oxygenated what happes to Hb
when dHb it is paramagentic but when oxygenated it is diamagnetic and in a low spin state
Explain Haemodynamic response function?
Region of brain is active there is an increase in regional blood flow, blood volume , susceptabiliyu and oxygen consumption increases slghtlty
Causes net increase in venous oxygenation and decrease in dHb so Increase in T2* Therefore higher tissue signal
HRF is the time course of BOLD to change from stimulation
What is OEF
difference in blood saturation beweeen arterial and venous outflow
Oxygen consumpton eqn using Fick principle
Flow *OEF
What are the three key features of hrf
- transient undershoot before intial rise (deoxy dip) due to O2 comuption causing decrease in venous oxygenation before blood flow rise has effect
- haemodynamic delay in primary cortical regions
takes 5-8 sec to reach max signal
the 5-9 sec from stimulus cessation for signal to fall to 10% above base
Prolonged undershoot after end of simulation due to stretching of venous vessels
What is blocked fMRI design
stimuli clustered togetjer in clocks 15-60s
allowing appearance of continuous activation during block
period os stimulation = period od rest ]-alterate
What is event related design in fMRI?
response to individual event imaged
interstimulus inteval 20s
What is resting state fMRI design?
no specific stimulu
variation in signal recorded
susceptability effect - field stength eqn
delta B = suceptability *B
Image relignment eqn
What data is disregarded
h - sum (u-v)^2
ref imagien - image to be registered
dATA SHOWINF MOLTIOn> 1 voxel
Statstical analysis of BOLD
(Son-Soff)/Soff *100
