Methods of Neuroscience (lecture) Flashcards
What do gradient coils do?
Create controlled spatial variation in the strength of the magnetic field in order to localize where the reflected energy came from in the brain.
What are the first steps in MRI
- alignment into parallel and antiparallel of the protons in H atoms by the magnetic field. (net vector up)
- radio frequency pulse to get the precession in phase by resonance + spin flip (more antiparallel) which leads to
- knockdown of net vector into the transversal plane (high energy)
How does T1 relaxation work?
RF wave turned off leading to; spins going back to parallel (longitudinal), releasing energy in form RF picked up by coil. Different tissues have different rates, leading to signal differences.
fat = bright
bone, water = dark
How does T2 relaxation work?
spin-spin relaxation: the spins get out of phase at a different rate, those that are slower to go out of phase have stronger signal. Water = bright, bone = dark
Bc out of phase, net vector goes from transversal direction to more longitudinal (releases energy)
Which direction does the net vector need to be in in order for the MRI to read a signal
transversal plane
What is one of the variables that changes when you have a Tesla 9 instead of a Tesla 3?
Ratio parallel: antiparallel after alignment gets smaller
What is echo time? TE?
the time at which you determine contrast that delivers maximum signal difference between different tissues, the time following excitation to detect the signal
What is repetition time TR?
time in between excitation
T1, T2, TR, TE: which are tissue parameters and which are experimental parameters?
t1 and t2 tissue
te and tr experimental
How does functional imaging with BOLD work?
oxygenated blood is not magnetic
deoxygenated blood is magnetic -> distorts magnetic field leading to less signal
T2 weighted: oxygenated blood shows slower decay, gets out of phase slower.
what is the hemodynamic response function?
mathematical graph following the strength of BOLD response. In brain areas that are used for the current task, first there is a slight dip (more oxygen used than available), than a peak after a few seconds (6s) due to overshoot, before going back to baseline.
how is the HRF related to different fmri designs? what is the main reason to choose for event-related?
In event design a single stimulus category is showed, leading to a simple HRF (stick function)
In blocked design, a stimulus type is shown for longer durations, leading to a boxcar function
The choice for event related is often done when you have to categorize trial condition post hoc, so that you get stick HRF and are able to discern the effect of the different conditions without them adding up.
