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MRI AllinOne > Data Acquisition and Processing > Flashcards

Data Acquisition and Processing Flashcards

1
Q

What are the 5 basic steps to a pulse sequence

A 
alignment
excitation slice selection
phase encoding
rephasing slice selection
frequency encoding
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2
Q

What hardware performs alignment in a pulse sequence

A

main magnet

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3
Q

What hardware performs excitation slice selection in a pulse sequence

A

RF coil and gradients

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4
Q

What hardware performs phase encoding in a pulse sequence

A

phase encoding gradient

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5
Q

What hardware performs rephasing slice selection in a pulse sequence

A 
RF coil (for SE)
gradients (for GE)
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6
Q

What hardware performs frequency encoding in a pulse sequence

A

frequency encoding gradient

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7
Q

What are the 2 types of pulse sequences

A

spin echo and gradient echo

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8
Q

Which pulse sequence uses a 90° excitation pulse followed by one or more 180° rephasing pulses in order to generate one or more spin echos

A

spin echo

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9
Q

What are the 3 types of spin echos

A

conventional spin echo (CSE)
fast spin echo (FSE)
inversion recovery (IR)

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10
Q

This type of spin echo uses a 90 alpha pulse and a singe 180 rephasing pulse per TR

A

conventional spin echo

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11
Q

How many lines of K space are filled per TR during a conventional spin echo

A

one (resulting in longer scan times, so CSEs are usually only T1 weighted)

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12
Q

What are the advantages of a conventional spin echo

A

excellent image quality

“true” image weighting (since there is no signal averageing of multiple echos)

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13
Q

What are the disadvantages of a conventional spin echo

A

long scan times (only 1 line of K space is filled per TR)

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14
Q

What are the TR and TE parameters for a T1 weighted CSE

A 
TR = 300-700 ms
TE = 10-30ms
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15
Q

What are the TR and TE parameters for a T2 weighted CSE

A 
TR = 2000ms+
TE = 80ms+
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16
Q

What are the TR and TE parameters for a PD weighted CSE

A 
TR = 2000ms+
TE = 20ms
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17
Q

Fast spin echoes (FSE) are also referred to as what

A

Turbo spin echoes (TSE)

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18
Q

Which pulse sequences use a 90ﾟ alpha pulse and multiple 180ﾟ rephrasing pulses per TR

A

Fast spin echoes (FSE) aka Turbo spin echoes (TSE)

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19
Q

What parameter is averaged during a fast spin echo

A

TE is averaged and creates an “effective TE”

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20
Q

Is it possible to acquire true image weighting during FSE sequences

A

no because the TEs for each echo are averaged

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21
Q

What are the advantages of an FSE sequence

A

Shorter scan times (multiple lines of K space are filled per TR)

decreased magnetic susceptibility artifacts

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22
Q

What are the 4 disadvantages of an FSE sequence

A

Increased motion artifact (sinse signal during motion is acquired multiple times)

increased image blurring (from signal averaging of long echo trains)

decreased SNR

decrease of ability to detect small hemorrhages (because of the reduction in magnetic susceptibility artifacts)

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23
Q

Which spin echo sequence combines FSE with a Partial Fourier technique in order to fill all lines of K space during a single TR period

A

Single shot fast spin echo (SS-FSE)

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24
Q

What are the advantages of a single shot fast spin echo (SS-FSE) sequence

A

Dramatic reduction in scan time

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25
Q

What are the disadvantages of single shot fast spin echo (SS-FSE) techniques

A

Increased tissue heating

increased SAR (due to the extra RF rephasing pulses)

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26
Q

What does the acronym DRIVE stand for

A

Driven Equilibrium Fourier Transform

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27
Q

Which pulse sequence uses a reverse flip angle excitation pulse after the echo train (90-180-180-90), thus driving any residual transverse magnetization into the longitude plane so that it cannot be further excited at the beginning of the next TR cycle

A

Driven Equilibrium Fourier Transform (DRIVE)

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28
Q

Which pulse sequence yields a hyper intense fluid signal when compared to standard FSE pulse sequences

A

Driven Equilibrium Fourier Transform (DRIVE)

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29
Q

What are the TR and TE parameters for a T1 weighted FSE

A

TR = 300-700 ms

effective TE = minimum

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30
Q

What are the TR and TE parameters for a T2 weighted FSE

A

TR = 3000-10000 ms

effective TE = 80-140ms

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31
Q

What are the TR and TE parameters for a PD weighted FSE

A

TR = 3000-10000 ms

effective TE = minimum

32
Q

A pulse sequence that begins with a 180ﾟ inverting pulse followed by a conventional spin echo (CSE) or fast spin echo (FSE) pulse sequence.

A

Inversion recovery

33
Q

What 2 things are used to null the signal from certain tissues such as fat or fluid in an inversion recovery sequence

A

A 180ﾟinverting pulse

Time of inversion (TI)

34
Q

What are the 2 types of IR sequences

A

STIR

FLAIR

35
Q

The time between the 180ﾟ inverting pulse and the 90 alpha pulse is called what

A

Time of inversion (TI)

36
Q

What is occurring during the TI interval

A

longitudinal recovery - allowing more T1 relaxation between tissues (decreasing T1 contrast since more tissues relax to the longitudinal axis)

37
Q

Longitudinal recovery during an IR sequence does what to T1 contrast

A

Decreases it - since more tissues relax to the longitudinal axis

38
Q

When the 90ﾟ RF pulse is applied during an IR sequence, what happens to tissues nearest the transverse plane

A

They will flip an additional 90ﾟ- moving past the transverse plane into full saturation thus becoming nulled out

39
Q

What happens to tissues that were able to relax nearer the longitudinal plane when the 90ﾟ RF pulse is applied during and IR sequence

A

they will be flipped 90ﾟ into the transverse plane where they will contribute to image signal

40
Q

The TI interval that is selected represents what

A

What tissues will be nulled

41
Q

What determines image weighting during an IR sequence

A

The TR and TE - just like all other sequences

42
Q

What does STIR stand for

A

Short TI inversion recovery
or
Short TAU inversion recovery

43
Q

An inversion recovery pulse sequence that uses a short TI of approximately 100-175ms

A

STIR

44
Q

Which inversion recovery sequence is used to null fat

A

STIR

45
Q

What is the TI for a STIR sequence

A

100-175ms

46
Q

How will CSF and fat appear on a STIR

A

CSF will be bright

fat will be dark

47
Q

Which inversion recovery pulse sequence uses a long TI of 1700 - 2200ms

A

FLAIR

48
Q

What does FLAIR stand for

A

Fluid attenuating inversion recovery

49
Q

How does fat and CSF appear on a FLAIR

A

Fat is bright

CSF is dark

50
Q

What weighting does a STIR have

A

T1

51
Q

What weighting does a FLAIR have

A

T2

52
Q

What is the TI for a FLAIR

A

1700 - 2200ms

53
Q

What does GRE stand for

A

Gradient recall Echo

54
Q

What are the 2 acronyms for gradient pulse sequences

A

GRE (Gradient recall Echo)

GE (Gradient echo)

55
Q

What sequence uses an alpha pulse with a variable flip angle, as well as the frequency encoding gradient - instead of a 180ﾟ RF pulse - for rephrasing

A

Gradient echo

56
Q

What does a gradient echo use to rephrase spins

A

The frequency encoding gradient

57
Q

What do spin echoes use to rephase spins

A

A 180ﾟ RF pulse

58
Q

Can gradients compensate for magnetic field inhomogeneities

A

no

59
Q

Due to the inability of gradients to compensate for magnetic field inhomogeneities, all gradient images have some extent of what type of contrast

A

T2*

60
Q

Are gradient pulse sequences sensitive to flow

A

yes

61
Q

Are gradient echo pulse sequences fast or slow

A

Fast (commonly used for breath hold sequences)

62
Q

What are the 5 types of gradient echoes

A

Conventional gradient echo (CGE)

Steady state (SS)

Fast gradient echo (FGE)

Balanced gradient echo (BGE)

Echo planar imaging (EPI)

63
Q

How many lines of K space are filled per TR during a conventional gradient echo

A

only 1

64
Q

What type of gradient echo pulse sequence uses 2 excitation pulses, with variable flip angles, at TR time intervals less than the T1 and T2 times of the body’s tissues in order to maintain residual transverse magnetization for the creation of a stimulated echo

A

Steady state sequences

65
Q

If a steady state sequence uses 2 90ﾟ excitation pulses, the echo created by the application of the 2nd pulse is referred to as a

A

Hann echo

66
Q

How many times is the frequency encoding gradient used for rephasing during a steady state sequence

A

once

67
Q

Steady state sequences are called as such because they maintain partial longitudinal and transverse magnetization at all times, never allowing the NMV to return to the longitudinal axis. T/F

A

true

68
Q

What type of steady state pulse sequence uses 2 alpha pulses with variable flip angles, as well as subsequent gradient rephasing where only the gradient echo (FID) is sampled

A

Incoherent (spoiled) gradient echo

69
Q

How many types of steady state sequences are there

A

3

70
Q

Name the 3 types of steady state sequences

A

Incoherent (spoiled) gradient echo

Coherent gradient

Steady state free precession

71
Q

This type of steady state pulse sequence prevents the stimulated echo from contributing to image contrast by spoiling (dephasing) it through the use of RF spoiling or gradient spoiling (application of all 3 gradients

A

Incoherent (spoiled) gradient echo

72
Q

Incoherent gradient echo sequences are typically used for what type of weighting

A

T1, sometimes PD

73
Q

What are the advantages to using an incoherent (spoiled) gradient echo

A

Very fast (making breath holds possible)

very sensitive to flow (good for angiography)

74
Q

What are the disadvantages to using an incoherent (spoiled) gradient ago

A

Increased magnetic susceptibility artifacts

Produce loud gradient noise

75
Q

What is the flip angle used for incoherent gradient echoes

A

30-45ﾟ

76
Q

What TR is used for an incoherent gradient echo

A

20-50ms

77
Q

What TE is used for an incoherent gradient echo

A

5-10ms

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