WITH ANSWERS GRADED A+
✔✔Define TR - ✔✔The time from the initiation of one RF pulse starting a sequence, to
the next
✔✔Define TE - ✔✔Time from the application of the RF pulse to the peak of the signal
induced in the coil
✔✔Examples of intrinsic contrast parameters - ✔✔T1, T2, PD, flow, ADC
✔✔Examples of extrinsic contrast parameters - ✔✔TR
TE
Flip angle
TI
Turbo factor/echo train length
b value.
✔✔Explain T1 recovery - ✔✔Caused by hydrogen nuclei giving up their energy to the
surrounding environment (spin-lattice transfer), NMV realigns to Bo
✔✔T1 recovery time - ✔✔time taken for 63% of the longitudinal magnetization to
recover
✔✔Explain T2 decay - ✔✔Caused by magnetic fields of neighbouring nuclei interacting
with each other (spin-spin relaxation) the transverse magnetization dephases
✔✔T2 decay time - ✔✔time it takes for 63% of transverse magnetization to decay,
leaving 37% still in phase
✔✔T1 times of water and fat - ✔✔Water- 2500ms
Fat - 200ms
✔✔T2 times of water and fat - ✔✔Water-2500ms
Fat-100ms
✔✔Proton density of a tissue - ✔✔is the number of mobile hydrogen protons per unit
volume of that tissue.
✔✔2 factors that T1 and T2 relaxation depend on - ✔✔-if molecular tumbling rate
matches the larmour frequency of hydrogen = good energy transfer
-if molecules are closely packed together
, ✔✔Explain why fat and water appear different on images - ✔✔-Fat has molecules that
are closely packed together and tumbling rate is slow which better matches the larmour
frequency so NMV recovers fast and and magnetic moments dephase quickly (T1 and
T2 times are short)
-Water has molecules that are spaced apart and tumbling rate is fast so doesn't match
the larmour frequency so NMV recovers slow and magnetic moments dephase slowly
(T1 and T2 times long)
✔✔Define T1 contrast - ✔✔the image contrast comes from the differences in the T1
times of the tissues - T1 contrast is prominent when vectors do not fully recover their
longitudinal magnetization (short TR)
✔✔Appearances of fat and water on T1 - ✔✔Fat - bright, recovers faster than water &
more magnetization to be flipped into transverse plane
Water- dark, recovers slower so less magnetization flipped into transverse plane
✔✔Partial saturation and full saturation - ✔✔Partial - when NMV is pushed beyond 90°
Full- when NMV is pushed full 180°
✔✔Steady state - ✔✔vectors recover to the same point and have the same amount of
transverse magnetization - once the steady state is achieved the signals are detected
by the receiver coil
✔✔T1 contrast is controlled by __
T2 contrast is controlled by __ - ✔✔TR
TE
✔✔Define T2 contrast - ✔✔image contrast comes from the differences in the T2 times
of the tissues - T2 contrast is prominent when tissues have more time to decay (long
TE)
✔✔Appearances of fat and water on T2 - ✔✔Fat- dark, T2 time is faster (short) so more
dephasing and less coherent transverse magnetization
Water- bright, T2 time of water is longer so there is more coherent (in-phase) transverse
magnetization
✔✔Which weighting is used after administration of contrast - ✔✔T1 weighting
✔✔Short TR and short TE produces - ✔✔T1 weighting
✔✔Long TR and long TE produces - ✔✔T2 weighting
✔✔PD weighting - ✔✔Depends on the differences in mobile hydrogen protons per unit
volume of tissue