Unit 5 Flashcards
What is RF pulse?
a burst of radiofrequency energy
What is Net Magnetization relaxation?
the return of M to equilibrium as it releases absorbed RF (T1), and loses energy (T2)
What is free induction decay?
simple signal given off by the relaxation of M to equilibrium
What is spin/proton density?
relative number of protons in a sample
What is spin echo?
signal given off by the relaxation of M to equilibrium after a refocusing pulse
What is T1 relaxation relaxation/longitudinal recovery?
regrowth of net magnetization along the Z axis
What is spin-lattice relaxation?
process of RF being dissipated (T1 relaxation)
What is T2 relaxation/transverse decay?
decay of transverse magnetization
What is spin-spin relaxation?
process of spins interacting w/ each other => phase changes (T2 relaxation)
What is T2* relaxation?
transverse decay in presence of B0 inhomogeneities
What is phase?
degree to which spins are precessing
Why is T2* relaxation shorter than T2 relaxation?
B0 inhomogeneity increases dephasing
Which relaxation is most affected by B0 inhomogeneity?
T2*
At what time is true T1 relaxation measured?
at 63% of regrowth
At what time is true T2 relaxation measured?
at 63% of decay (37% remaining)
Which substance has the shorted T1 and T2 times?
fat
Which substance has the longes T2 and T2 times?
water
Which substance is bright on T1 weighted image?
fat
Which substance is bright on T2 weighted image?
water
How do water and fat nuclei experience magnetic fields?
Fat nuclei experience a lower magnetic field (C offers slight buffer)
Water nuclei experience a higher magnetic field (O exposes H)
True/False: Tissues w/ long T1 times appear bright on T1 weighted image.
false - appear dark
True/False: Tissues w/ long T2 times appear bright on T2 weighted image.
true
Which flip angle RF pulse creates a FID?
90 or less
Which flip angle RF pulse creates a spin-echo?
180
Which type of relaxation (weighted image) is created by spin-spin interactions and B0 inhomogeneity?
T2*
Which type of relaxation (weighted image) is created by only spin-spin interactions?
T2
