fMRI and long term memory Flashcards
What are the safety concerns about an fMRI? (6)
strong magnetic field (induce current in metal objects)
superconductor quench (helium evaporation)
changing magnetic fields (current induction)
radio frequency coil (specific absorption rate, don’t want to use too much of this)
claustrophobia
Noise
How many tesla is an fMRI machine
1.5T
What is an RF?
“opera singer with wine glass”
matter itself has a frequency in which it absorbs energy (just not sound anymore like opera singer) but in this case
targeting Hydrogen
what is a pulse sequence?
A sequence of sending energy in and changing the magnetic fields gradient very quickly
what makes in fMRI loud
turning the magnets on and off really fast
where the information is coming from in the brain is encoded in terms of what?
frequency
when you record the signals what is the initial problem?
how do we solve this
All the signals from all over the brain are mixed together
change it from representing frequency to representing location with a 2D fourier Transform
MATH!
a single dot in the K-space image represents what in real space
A series of waves
what determines in the image is lighter of darker
it shows the density of Hydrogen in different areas on the brain (proton density) dependent on water
the density is much lower in the air so it is darker
the lighter it is the denser it is
the types of tissue makes a difference too
the properties of tissue change how the energy is released from the matter.
how fast dephasing (decay) and recovery happens depends on what?
they tissue type (white matter grey matter)
by changing the timing of the RF pulse (TR) or the data acquisition (TE) we can do what?
we can emphasize either the density of protons or other types of tissues such as white and grey matter.
T2 weighted imaging shows what?
water very bright
T1 imaging shows what?
Grey and white matter stand out from one another and water is black
used most for structural imaging
proton density weighted shows what?
whatever has the most hydrogen is the brightest (water)
What does BOLD contrast stand for?
Blood oxygenation level dependent contrast
How does BOLD contrast work/ dependent on?
oxygenated hemoglobin and deoxygenated hemoglobin respond differently
this is due to the iron
how does oxygenated hemoglobin show up in a picture, what are its characteristics? (2)
clear
diamagnetic
zero magnetic moment
how does deoxygenated hemoglobin show up in a picture? what are its characteristics? (5)
Blurry
Paramagnetic
significant magnetic moment
greater magnetic susceptibility
causes faster T2 decay
neural activity causes what?
Firing, this uses O2 and will make the blood vessels in that one point in the brain to dilate. this will increase the flow of oxygenated blood.
neurons fire and at what times does deoxygenated hemoglobin hit a low? what happens at this point?
around 6 seconds
the MRI image is the best
when deoxygenated hem. levels go down what happens to the MRI signal?
It goes up, this is due to the deoxygenated hem. interfering with the picture
BOLD signal is better for what?
better at representing the local field potential than the actual AP.
better for post synaptic potentials
What is the first step in processing fMRI data?
slice timing correction
-need to correct for the fact that different slices are collected at slightly different times
What is the second step in processing fMRI data?
Realignment (your head may be moving a little bit)
What is the third step in processing of fMRI data?
Reslicing
after realignment we need to reslice to match up Voxels
What is the fourth step in processing fMRI data?
Coregistration
align functional images to structural images
What is the fifth step in processing fMRI data?
Normalisation
wrap each subject’s brain into a standard template
match all the brains up
do this with softwear
what is the sixth step in processing fMRI images?
Smoothing
deal with remaining inconsistencies by smoothing (i.e. blurring) the images
what does a fMRI block design allow you to do?
one group gets a fearful face
then a bunch of happy faces
bunch of neutral faces
what is an event related design
individual faces one after another all in a random order
mix in some time delays “jittering”
what does a mixed design do?
it is a mix between even related and block design
