Module 2 Flashcards
occurs when an object with a certain precessional frequency is subjected to a force that has the same precessional frequency
resonance
excitation that matches the precessional frequency of hydrogens atoms at a certain filed strength
RF pulse
can cause some energy of low spin up to change to high spin up
application of RF pulse
higher RF pulse to match processional frequency
higher strength magnet
RF pulse does not match larmor frequency of hydrogen atom
no resonance occurs
Resonance occurs, NMV moves out of alignment with B(o)
at angle with B(o)
flip angle
most common fip angle
90
main magnetic filed plane
longitudinal
fip angle plane
transverse plane
when magnetic moments are on same point in precessional path
maximum signal
in phase
coherent
magnetic moments are not on teh same point in precessional path
minimal or no signal
out of phase
in-coherent
RF pulse turned off NMV realigns with B(o)
relaxation
process when hydrogen loses energy
atoms that moved to high state will return to low state
relaxation
longitudianl plane
recovery
transverse plane
decay
occurs simultaneously but independently as relaxation
takes place in transverse magnetization
decay
hydrogen nuclei start to realign with B(o) in teh longitudinal plane
out of phase
transverse magnetization begins to decay
logitudinal regrowth
transverse dephasing
effects of RF pulse removal
relaxation time for 63% of NMV of tissue to recover
T1 recovery
spin lattice relaxation
relaxation time for transverse plane to decay to 37%
T2 decay
spin spin relaxation
relaxation due to nuclei giving up energy to surrounding environment
spin lattice relaxation
T1 recovery
interaction of spins nuclei with each other
spin spin relaxation
T2 Decay
independent of each other
T2 never exceeds T1
relaxation time
decay of FID signal
shorter than T2 because of dephasing due to magnetic field inhomogenities and T2 decay
T2*
signal induced in coil from patients tissues (hydrogen atoms)
measure in coulombs
free induction decay
FID
plot of MR signal intensity as a functino of time
spatially reconstructed into an image though a mathmatical function
2D or 3D fourier transformation
FID
free induction decay
results in a nuclear magnetic spectrum in the frequency domain
Fourier transformation of FID
