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MRI > MRI Physics 4 > Flashcards

MRI Physics 4 Flashcards

1
Q

In which directions can PC MRA be flow sensitive

a. through plane
b. in plane
c. a and b
d. none of the above

A

c. a and b

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2
Q

Which of the following statements are true concerning venous flow imaging with bright blood TOF-MRA
I. slower than arterial flow
II. lower flow related enhancement than arterial flow
III. cannot be imaged with TOF

a. I only
b. I and II only
c. II and III only
d. I II and III

A

b. I and II only

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3
Q

If one desires to do a set of axial 2D-TOF MRA scans for the saphenous veins, where should sat pulses be placed in relation to the imaging region

a. inferior
b. superior
c. a and b
d. none of the above

A

b. superior

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4
Q

Pulsating motion is best described as

a. acceleration
b. stagnation
c. jerk
d. none of the above

A

c. jerk

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5
Q

Time of Flight (TOF) effects can lead to

a. MRI signal loss from flow
b. MRI signal gain from flow
c. a and b
d. none of the above

A

c. a and b

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6
Q

In order to make every slice and “entry slice”, the slice excitation wave should be performed

a. co current
b. counter current
c. inferior to the FOV
d. superior to the FOV

A

b. counter current

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7
Q

Which of the following is not a mechanism for MRI signal loss in flow

a. turbulence
b. flow compensation
c. dephasing effects
d. none of the above - all cause signal loss

A

b. flow compensation

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8
Q

Which timing parameter is critical for “black blood” MRA

a. TR
b. TE
c. TI
d. none of the above

A

b. TE

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9
Q

The most common procedure for the Circle of Willis is _____, while the most common procedure for the carotids is _____.

a. 2D-TOF, 2D-TOF
b. 2D TOF, 3D TOF
c. 3D TOF, 2D TOF
d. 3D TOF, 3D TOF

A

c. 3D TOF, 2D TOF

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10
Q

Application of pre-sat pulses during a flow imaging sequence will ____ SAR and ____ the number of slices per TR period.

a. decrease, decrease
b. decrease, increase
c. increase, decrease
d. increase, increase

A

c. increase, decrease

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11
Q

The usual MRI picture displayed on the console is the

a. phase image
b. magnitude image
c. a and b
d. none of the above

A

b. magnitude image

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12
Q

If the slice thickness is increased, then high velocity signal loss in “black blood” TOF-MRA tends to

a. decrease
b. stay the same
c. increase
d. none of the above

A

a. decrease

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13
Q

Magnetization Transfer directly affects which spins

a. free water
b. fat
c. protein bound water
d. protein bound fat

A

c. protein bound water

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14
Q

Intra voxel dephasing occurs for which kind of flow

a. turbulent
b. laminar
c. a and b
d. none of the above

A

c. a and b

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15
Q

In PC MRA flow velocity is mapped into the

a. frequency
b. phase
c. a and b
d. none of the above

A

b. phase

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16
Q

For SE imaging of flow, odd echo dephasing will occur for which kind of flow

a. turbulent
b. laminar
c. a and b
d. none of the above

A

c a and b

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17
Q

Which of the following techniques will be useful for reducing intra voxel dephasing
I. increase voxel size
II. increase TE
III. use gradient moment nulling (GMN)

a. I only
b. I and II only
c. III only
d. I II and III

A

c. III only

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18
Q

Bends in the ICA can mimic stenosis in “bright blood” MRA because of

a. turbulent flow
b. vortex flow
c. plug flow
d. accelerated flow

A

d. accelerated flow

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19
Q

Even Echo Rephasing works for SE sequences with

a. symmetric echoes
b. asymmetric echoes
c. a and b
d. none of the above

A

a. symmetric echoes

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20
Q

If the following orders of gradient lobes are turned on for the same amount of time,which set of relative amplitudes will compensate for accelerated fluid motion

a. 1 neg, 1 pos
b. 1 pos, 2 neg, 1 pos
c. 1 neg, 3 pos, 3 neg, 1 pos
d. 1 neg, 3 pos, 1 neg, 3 pos

A

c. 1 neg, 3 pos, 3 neg, 1 pos

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21
Q

In order to image flow in the jugular veings using 2D TOF MRA slices should be acquired in what order

a. I to S
b. S to I
c. A to P,
d. P to A

A

a. I to S

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22
Q

If A0 is the vessel radius, r is the cylindrical radial coordinate, and V0 is a constant, then the laminar flow velocity V(r) is given by

a. V(r) = V0
b. V(r) = V0(1-(r/A0))
c. V(r) = V0(1-(r/A0)^2)
d. none of the above

A

c. V(r) = V0(1-(r/A0)^2)

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23
Q

Sensitivity to flow near the edge of a vessel could best be accomplished with ___, while flow near the lumen center is best determined with ______.

a. low VENC, low VENC
b. low VENC, high VENC
c. high VENC, low VENC
d. high VENC, high VENC

A

b. low VENC, high VENC

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24
Q

Shaded surface Display is

a. an RF artifact
b. an MRA display method
c. a and b
d. none of the above

A

b. an MRA display method

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25
Q

Using cardiac gating, which parameter is set by the patient heart rate

a. TR
b. TE
c. TI
d. a and c

A

a. TR

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26
Q

For “bright blood” MRA, which pulse sequence is more likely to be used.

a. Incoherent GRE
b. Coherent GRE
c. SE
d. EPI

A

a. incoherent GRE

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27
Q

The most common artifact associated with MOTSA is

a. ghosting
b. aliasing
c. venetian blind
d. all of the above

A

c. venetian blind

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28
Q

Which is the critical time parameter for flow related enhancement

a. TR
b. TE
c. TI
d. none of the above

A

a. TR

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29
Q

“Flow Encoding” in PC MRA refers to

a. readout
b. spoilers
c. reqinders
d. gradient sensitizing directions

A

d. gradient sensitizing directions

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30
Q

Which of the following effects reduce flow saturation in MRA scans
I. increasing the FA
II. decreasing TR
III. using gadolinium contrast

a. I and II only
b. I and III only
c. III only
d. I II and III

A

c III only

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31
Q

“Black Blood” MRA uses

a. minimum intensity perception
b. maximum intensity perception
c. minimum intensity projection
d. maximum intensity projection

A

c. minimum intensity projection

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32
Q

The tau time is given by which expression

a. TE
b. TE/2
c. TR/2
d. .693 T1

A

b. TE/2

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33
Q

the “in flow effect” in GRE flow sequences decreases with

a. thin slices and slow flow velocities
b. thin slices and fast flow velocities
c. thick slices and slow flow velocities
d. thick slices and fast flow velocities

A

c. thick slices and slow flow velocities

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34
Q

If the MRI signal is greater than some threshold, then MIP plots the brightest signal in

a. each slice
b. each pixel channel
c. the imaging volume
d. none of the above

A

b. each pixel channel

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35
Q

In PC MRA flow contrast with stationary tissue occurs because different phases arise from turning on

a. RF
b. gradients
c. a and b
d. none of the above

A

b. gradients

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36
Q

Another name for Laminar flow is

a. plug flow
b. vortex flow
c. parabolic flow
d. stagnation point

A

c. parabolic flow

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37
Q

A large slice thickness is ____ for FRE

a. good
b. bad
c. indifferent
d. none of the above

A

b. bad

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38
Q

What will the effect of a very low flow velocity V be on “bright blood” MRA

a. increase signal
b. no effect
c. decrease signal
d. none of the above

A

c. decrease signal

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39
Q

For 2D TOF MRA the MRI signal will be largest if the flow is directed

a. parallel to the slice
b. perpendicular to the slice
c. a or b
d. none of the above

A

b. perpendicular to the slice

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40
Q

For SE sequence with high velocity loss, what is the critical velocity above which no signal is produced by flowing spins in a slice with thickness z

a. (2z)/TE
b. (2z)/TR
c. TE/2z
d. TR/2z

A

a. 2z/TE

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40
Q

In bright blood 2D MRA sequences, how are the slices acquired

A. Multiplanar
B. sequential
C. A and B
D. None of the above

A

B. sequential

41
Q 
In bright blood MRA sequences, TE is kept short principally because
A. Emphasizes T2W
B. minimizes high velocity loss
C. Minimizes dephasing effects
D. None of the above
A

C. Minimizes dephasing effects

42
Q 
Flow saturation is a greater problem for
A. 2D TOF MRA
B. 3D TOF MRA
c. A and B
D. None of the above
A

B. 3D TOF MRA

43
Q 
Supposing one uses ECG gating.  If the heart rate is for 45 bpm, what is the period T between heart beats
A. .75s
B. 1.0s
C. 1.33s
D. 1.50s
A

C. 1.33s

44
Q 
In MRA applications, fluid velocities are typically given in which set of units
A. Mile/hr
B. meter/sec
C. Cm/sec
D. Mm/sec
A

C. cm/sec

45
Q 
First order flow compensation cannot compensate for which of the following flows?
A. Laminar
B. accelerated
C. Turbulent
D. B and C
A

D. B and C

46
Q

How many different directions can be flow compensated in an MRI scan
I. Readout
II. Phase encoding
III. Slice

A. I only
B. I and II only
C. III only
D. I II and III

A

D. I II and III

47
Q

Suppose that 2D MRI scan is prescribed. now one wishes to add flow compensation. which of the folowing parameters must increase

a. T1
b. T2
c. min. TE
d. none of the above

A

c. min TE

48
Q

In order to reduce phase errors, how many acquisitions are typically acquired for PC MRA

a. 1
b. 2
c. 4
d. none of the above

A

b. 2

49
Q

Constant velocity is an example of _____ motion

a. 0 order
b. 1st order
c. 2nd order
d. 3rd order

A

b. 1st order

50
Q

Which scan acquisition time would usually be the longest for MRA of the COW

a. 2D TOF
b. 3D TOF
c. 2D PC
d. 3D PC

A

d. 3D PC

51
Q

A volume acquistion in MRI requires what kind of data processing methods

a. 1D FT
b. 2D FT
c. 3D FT
d. none of the above

A

c. 3D FT

52
Q

which pulse sequences are typically used for PC MRA

a. incoherent GRE
b. coherent GRE
c. incoherent SE
d. coherent SE

A

a. incoherent GRE

53
Q

Gadolinium is primarily what kind of contrast agent

a. T1 shortening
b. T2 shortening
c. T1 lengthening
d. T2 lengthening

A

a. T1 shortening

54
Q

The saturation of flowing spins in “bright blood” MRA increases if which of the following is performed
I. TR is decreased
II. FA is decreased
III. Gadolinium contrast is used

a. I only
b. I and III only
c. II only
d. II and III only

A

a. I only

55
Q

Choose the proper order for 3D TOF MRA pulse sequence events from earliest to latest

a. rewinder, alpha pulse, presat pulse
b. alpha pulse, presat pulse, rewinder
c. presat pulse, rewinder, alpha pulse
d. presat pulse alpha pulse, rewinder

A

d. presat puilse, alpha pulse, rewinder

56
Q

For which “bright blood” TOF MRA sequence would the FA typically be lower

a. 1D
b. 2D
c. 3D
d. 4D

A

c. 3D

57
Q

If r is a radial coordinate acros the vessel lumen, then the flow velocity v(r) being independant of r best describes

a. laminar flow
b. plug flow
c. turbulent flow
d. vortex flow

A

b. plug flow

58
Q

Even echo rephasing is most useful for which kind of imaging

a. T1W
b. PD
c. T2W
d. a and b

A

c. T2W

59
Q

Which of the following MRA scans typically equire 3D methods
I. carotids
II. AVM
III.lower extremity vasculature

a. I only
b. II only
c. II and III only
d. I II and III

A

b. II only

60
Q

In and MRA of the COW, Magnetization Transfer is uded to suppress signal from which tissues

a. White matter
b. Gray matter
c. flowing protons
d. a and b

A

d. a and b

61
Q

the TOF MRA method with higher SNR is ___ and with shorter scan time is ____

a. 2D, 2D
b. 2D, 3D
c. 3D, 2D
d. 3D, 3D

A

c. 3D, 2D

62
Q

for a “run off” MRA which scan method would normally be used

a. 2D TOF
b. 3D TOF
c. 2D PC
d. 3D PC

A

a. 2D TOF

63
Q

Gadolinium contrast will have what effect on TOF MRA scans

a. decrease flow contrast
b. no efect
c. increase flow contrast
d. none of the above

A

c. increase flow contrast

64
Q

“co curent” refers to

a. GRE
b. GREW
c. SE
d. SEW

A

d. SEW

65
Q

Hich velocity signal loss is the dominant process when using which kinds of pulse sequences in flow imaging

a. gradient echo
b. spin echo
c. echo planar
d. none of the above

A

b. spin echo

67
Q

The critical factor that determines the kind of flow in a vessel is

a. fluid velocity
b. fluid viscosity
c. reynolds number
d. none of the above

A

c. reynolds number

68
Q

Advantages of 3D TOF MRA compared to 2D TOF MRA typically include which of the following?
I. higher spatial resolution
II. sensitivity to slower flow
III. larger coverage

a. I only
b. I and III only
c. II and III only
d. I II and III

A

a. I only

69
Q

suppose that the flow in a vessel is laminar and that the maximum velocity in the lumen is Vmax. then the average velocity in the vessel is

a. 0
b. Vmax/4
c. Vmax/2
d. Vmax

A

c. Vmax/2

70
Q

Which of the following are typically advantages of PC MRA compared to TOF MRA
I. sensitivity to in plane flow
II. lower scan time
III. measurement of flow velocity

a. I only
b. I and III only
c. II and III only
d. I II and III

A

b. I and III only

71
Q

The gradient lobes used for flow encoding in PC MRA

a. can null higher order flow
b. are used for flow compensation
c. are bipolar
d. all of the above

A

c. are bipolar

72
Q

Which of the following cannot appear in a PC MRA pulse sequence

a. flow encoding gradients
b. flow compensation gradients
c. spoiler gradients
d. none of the above - all can appear

A

d. none of the above - all can appear

73
Q

MRI data is stored as

a. real numbers
b. imaginary numbers
c. complex numbers
d. none of the above

A

c. complex numbers

74
Q

If one desires to image the vertebral arteries, where are saturation pulses placed in relation to the imaging region

a. inferior
b. superior
c. a and b
d. none of the above

A

b. superior

75
Q

In order to extract flow speed V or direction from an MRA scan, one requires

a. magnitude image
b. phase image
c. a and b
d. none of the above

A

b. phase image

76
Q

Choosing a VENC is requires for

a. TOF MRA
b. PC MRA
c. GMN
d. b and c

A

b. PC MRA

77
Q

in an area of flow turbulence, the MRI picture will look

a. dark
b. bright
c. a or b depending on the imaging sequence
d. none of the above

A

a. dark

78
Q

if the flow proton spins are saturated in a 3D acquisition, the saturation will be greatest where?

a. entry side of imaging region
b. middle of imaging region
c. exit side of imaging region
d. none of the above

A

c. exit side of imaging region

79
Q

because of the short TR used for GRE sequences, stationary tissue surrounding vessel walls tends to have ____ magnetization. This creates ____.

a. unsaturated, low contrast
b. unsaturated, high contrast
c. saturated, low contrast
d. saturated, high contrast

A

d. saturated, high contrast

80
Q

Comparatively ____ VENC values are used for arteries, while _____ VENC values are used for veins.

a. small, small
b. small, large
c. large, small
d. large, large

A

c. large, small

81
Q

MIP means

a. minimum intensity perception
b. maximum intensity perception
c. minimum intensity projection
d. maximum intensity projection

A

d. maximum intensity projection

82
Q

Choosing to small a VENC will lead to which effect
I. ghosting
II. velocity aliasing
III. odd echo dephasing

a. I only
b. I and II only
c. II only
d. I II and III

A

c. II only

83
Q

If the eye vascular system is imaged, a problem with MIP might be

a. eye motion
b. high retro orbital fat signal
c. low spatial resolution
d. low SNR

A

b. high retro orbital fat signal

84
Q

TOF MRA is sensitive to flow

a. in the direction of the sensitizing gradients
b. in plane
c. through plane
d. all of the above

A

c. through plane

85
Q

MOTSA is used to combat

a. TOF MRA saturation
b. flow dephasing due to gradients
c. a and b
d. none of the above

A

a. TOF MRA saturation

86
Q

Which technique uses a ramped flip angle

a. GRE
b. TONE
c. MOTSA
d. all of the above

A

b. TONE

87
Q

Flow with erratic velocity values occurs in

a. laminar flow
b. plug flow
c. turbulent flow
d. b and c

A

c. turbulent flow

88
Q

Choose the correct ordering of the following maximum arterial flow velocities from slowest to fastest

a. aorta, femoral, vertebral
b. aorta, vertebral, femoral
c. vertebral, femoral, aorta
d. femoral, vertebral, aorta

A

c. vertebral, femoral, aorta

89
Q

The main problem with “bright blood” MRA techniques is

a. underestimation of stenosis
b. overestimation of stenosis
c. long scan time
d. low SNR

A

b. overestimation of stenosis

90
Q

If the TE = 50ms for a spin echo type of sequence, this suggests that an image of a flow signal could be acquired at the echo time

a. 50ms
b. 100 ms
c. 200 ms.
d. b and c

A

d. b and c

91
Q

Swirling motion distal to a stenosis could be described best as

a. vortex flow
b. eddy motion
c. a whirlpool
d. all of the above

A

d. all of the above

92
Q

The “entry phenomenon” relies on which kind of flowing proton spins entering a slice

a. saturated
b. unsaturated
c. a and b
d. none of the above

A

b. unsaturated

93
Q

Dephasing effects in “bright blood” MRA can best be minimized by

a. decreasing TE
b. increasing TE
c. decreasing TR
d. increasing TR

A

a. decreasing TE

94
Q

The MRI signal from calcified plaque in a vessel wall is

a. bright
b. gray
c. dark
d. depends on whether TOF of PC MRA is used

A

c. dark

95
Q

Magnetization transfer RF pulse frequencies are nearest

a. the free water resonance
b. 15 kHz from the free water resonance
c. 1500 kHz from the free water resonance
d. 1500 Hz from the free water resonance

A

d. 1500 Hz from the free water resonance

96
Q

“Black blood” MRA tends to ____ stenosis

a. underestimate
b. overestimate
c. a and b
d. none of the above

A

a. underestimate

97
Q

The units for VENC are

a. mm/s
b. cm/s
c. m/s
d. mi/hr

A

b. cm/s

98
Q

“venetian blind” is a

a. pulse sequence
b. MRA technique
c. artifact
d. b and c

A

c. artifact

99
Q

In a vessel with normal blood flow, the flow is best described as

a. laminar flow
b. plug flow
c. turbulent flow
d. a and b

A

a. laminar flow

100
Q

To increase the signal from flowing spins in a vessel lumen, it is best to prescribe slices

a. co-current
b. counter curent
c. a or b depending on TR
d. none of the above

A

b. counter curent

MRI (6 decks)

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