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MRI Physics 2 > Week 3 > Flashcards

Week 3 Flashcards

1
Q

which pulse sequence retains residual transverse magnetization and provides strong T2 contrast?

A

steady state GRE

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2
Q

what controls the steady state due to the short TR?

A

flip angle controls RF saturation

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3
Q

which pulse sequence destroys residual transverse magnetization and provides strong T1 contrast?

A

spoiled steady state GRE

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4
Q

When is spoiled steady state applied in the cycle?

A

at the end of each excitation cycle

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5
Q

which pulse sequence rewinds residual transverse magnetization to maintain coherence in SE and FSE sequences?

A

rewound steady state

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6
Q

When is a rewound steady state applied in the cycle? which direction?

A

at the end of each cycle

in the phase-encoding direction

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7
Q

which pulse sequence removes residual transverse magnetization with longer TE and provides true T2 contrast?

A

reverse-echo GRE

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8
Q

which pulse sequence uses gradient moment nulling to reduce flow artifacts, providing stable images in the presence of motion?

A

balanced GRE

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9
Q

which pulse sequence achieves very fast imaging sequences, especially in SE w/ 180-degree refocusing pulses?

A

echo planar imaging

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10
Q

which sequence use a 90-degree and 180-degree RF pulse sequence to refocus spins?

A

SE sequences

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11
Q

which sequence rely on a lower flip angle and do not use a 180-degree refocusing pulse?

A

GRE sequences

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12
Q

which sequence is more prone to inhomogeneity artifacts?

A

GRE sequences

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13
Q

what do GRE sequences achieve that allows for quicker imaging?

A

shorter TRs

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14
Q

which sequence has more contrast options?

A

SE sequences

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15
Q

which direction is balanced GRE is applied?

A

in the frequency or slice-select direction

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16
Q

what’s balanced GRE purpose?

A

realigns protons moving through the gradients w/ stationary protons

eliminating phase artifacts (ghosting)

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17
Q

what gives us the residual transverse magnetization?

A

steady state

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18
Q

what creates steady state? and how is it created?

A

Hahn echoes, by the continuous pulsing of RF energy

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19
Q

what does it mean to have short TR and TE settings?

A

RF pulses happen quickly, doesn’t not allow time to fully relax

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20
Q

True or False. Only Spin Echo Pulse Sequences can create this steady state, as they allow for fast pulsing required

A

False. only GRE

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21
Q

Name 2 speed up echo formation

A
  1. FSE
  2. EPI (echo planar imaging)
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22
Q

what technique is EPI?

A

single-shot

23
Q

what’s the main component of an EPI?

A

how we fill k-space, NOT echo formation

24
Q

Does EPI fill the entire slice of k-space in 1 TR period?

25
Q

what are the 3 studies EPI used for?

A
  1. diffusion
  2. perfusion
  3. functional MRI
26
Q

what can EPI possibly cause for pt?

27
Q

True or False. EPI is not prone to susceptibility artifacts and geometric distortions

28
Q

what’s the goal of IR?

A

eliminate/ suppress the signal from a given tissue

29
Q

Name 2 main IR sequences

A
  1. STIR
  2. FLAIR
30
Q

how is IR accomplished?

A

by choosing the ideal timing between an initial RF inversion pulse and an RF excitation pulse

31
Q

what is the time between the inversion pulse and the excitation pulse?

A

inversion time (TI)

32
Q

what is TI based on?

A

given tissue’s T1 relaxation time

33
Q

which IR sequence has shorter TI?

34
Q

which IR sequence has longer TI?

35
Q

what tissue does STIR suppress?

36
Q

what tissue does FLAIR suppress?

A

water/ CSF

37
Q

what is the non-cartesian filling that doesn’t add additional time?

A

keyhole

faster scan time = higher temporal reso

38
Q

what does a lower FA in GRE do?

A

allows T2* weighting
eliminate T1 weighting
longest TE possible

39
Q

what does a higher FA in GRE do?

A

allows T1 weighting
shortest TE possible

40
Q

what is Hahn echo created out of?

A

out of phase w/ new FID

41
Q

how do I allow the full longitudinal to recover?

A

don’t flip the NMV as far (gives it a head start)
lower flip angle

42
Q

what do I do to eliminate T1 waiting?

A

lower flip angle

43
Q

what does having a long TR do for us in Spin Echo Sequence?

A

allow longitudinal to recover fully
trade-off = lower T1 contrast

44
Q

how to get T1 in GRE?

A

high flip angle
short TE (0-5)

45
Q

how to get T2 in GRE?

A

low flip angle
long TE (15-30)

46
Q

how to get T2* in GRE?

A

low flip angle (5-25)
long TE (15-30)

47
Q

how to get PD in GRE?

A

low flip angle (5-25)
short TE (0-5)

48
Q

what are the 2 signals created at each RF pulse?

A
  1. FID
  2. Hahn echo
49
Q

what does FIESTA stand for?

A

Fully Balanced Steady State

50
Q

where is FIESTA applied in the cycle?

A

in the slice select in the frequency encoding direction

51
Q

which is the 3rd chemical suppression technique?

52
Q

what does Dixon technique use to suppress fat or water?

A

math based on in and out of phase echo collections

53
Q

what is this equation used to suppress?
1/2 IP + OP

A

fat suppressed (water only images)

54
Q

what is this equation used to suppress?
1/2 IP - OP

A

water suppressed (fat only images)

MRI Physics 2 (3 decks)

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