fMRI --> nuclear resonance imaging looool
--> nuclear resonance imaging looool
Aligignment of protons
protons spin rapidly around themselves (their own axis) called
--> generates weak magnetic field field
--> not ordered all spin in the direction they please :3!!
radio frequency pulse through magnetic coil of scanner = aligns them all into the same direction (phase locks the precession spins)
-----> in scanner aligned so north is parallel to body in direction of head and south parallel to laying body towards feet (about a bit more than half point north up and a bit less point half south up )
-------> BUT they are all synchronized and alligned north south axis
--> happens very fast, because the magnetic radio frequencies are strong ( just milliseconds)
then radio frequency is released and spin/ rotate / precess back/ bob back into their original precession (dephase) / spin around their own axis
--> called =
free induction decay
--> take longer to slowly precess back to their original spin than actually locking them with the radio frequencies ( but still takes milliseconds :3!!)
dephasing = T2
--> transverse relaxation time
--> milliseconds = very fast
--> water takes longer to dephase
--> for fMRI, more oxigen = more magnetic, so they lock into gradiant position quicker, and stay there longer after radia frequency deactivated, --> the dephasing takes much longer! (takes longer to dephase back into their original precession) this constitutes teh bold signal :3 !!
phaselocking = T1
--> longitudinal relexation time
--> used for anatomy (and in psychology studies
--> so time it takes till protons are aligned North (actually along the gradient being used atm) during emitting radio frequency through magnetic coil
because different molecules and tissues (eg. water in fat)
take more time to respond to radio frequency to realign their precession to the phase of the radio frequency (towards north south)
--> e.g. water protons in fat moves slower than water in blood for example, so they take longer to respond to radio frequency to realine to the phase (north south)
--> thats how we can get all the structual differences of fMRI scan
specifically we also adjust the magnetic / radiofrequency gradient from parallel to body to e.g. 1 or 2 degrees up Z axis
--> now the phase / direction to which protons will be locked is a bit different, with some protons being already closely aligned with their precession to that new gradiant, compared to others before
--> so now there is a different in tie it takes for them to align/ phase lock (T1) and dealign/dephase to their natural state afterwards :3 !!
--> depending on the amount of water there's different amount of protons (make sense as blood eg has more water, thus more amount of water protons than bone for example), so there will be a difference in response in strength of amplitude :3 !!
--> cause you put energy in form of radio waves into body, so when you stop the radio frequencies the unparalleled (high energy) protons flip back into parallel (low energy) mode and while doing so releasing th energy of the radio waves they have previously absorbed to the surrounding tissue.
--> if going on for too long it can raise the body heat of the person, kinda like in a microwave hah but you would have to be in scanner for 3 to 4 hours straight and fMRI machines automatically shut off at that point haha
--> btw only need to know how T1 and T2 works basically and that the T2* is what measures the bold signal :D:D:D:D:D !! SOOOO EASSSZZYY hahahah XD !!!
functional images = FMRI
anatomical images = MRI
--> contrast to noise ratio = signal differences between 2 tissues / noise (eg white matter - grey matter /(divided by) noise)
temporal resolution = how fast can it distinguish activity in brain ctivity
spatial resolution = accuracy of how exactly we can measure where something is coming from :3 !!
functional resolution = how well we can correlate physiologic stuff we measure to mental process (so fmRI indirect, eeg direkt :p ?) lol
Difference between T1 / T2
hemoglobin lag 6s for peak
BUT initial dip in oxygen through neural activation at about 0.5 seconds/ 5 ms
--> difficult to measure though (10 times to 100 times weaker than actual bold signal)
-------> would need lots of averaging to find it but then you find it for sure :3 !!
-------> higher tesla scanners could pick it up easier :) !! 7 Tesla 9.4 Tesla scanners for the win :D !!
spatial : up to 800 microns with t7 and t9.4 scanners
time resolved fMRI
--> can be used for mental chronometry
because bold response rises first in the area thats first active, then the next and so on.
by averaging a few trials this time code of bold rise can be disentangled and the brain areas frist active + their progression can easily be shown at the millisecond level :3 !!