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Physics > Chapter 6 > Flashcards

Chapter 6 Flashcards

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1
Q

Stationary nuclei always receive both excitation and rephasing pulses, but flowing nuclei present in the slice for the excitation may have exited the slice before rephasing. This is called ______________.

A

Time of Flight Phenomenon

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2
Q

TOF phenomenon results in a dark vessel. (T or F)

A

true

a dark vessel because nuclei that were present during the excitation are usually not present when the rephasing pulse is delivered and vice versa.

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3
Q

Which of the following effects does TOF depend on?

A

Velocity of flow, TE, Slice Thickness

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4
Q

The frequency difference between fat and water is called ___________ and can be used to specifically null the signal from either fat or water.

A

Chemical Shift

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5
Q

Which of the following is/are result(s) of time of flight?

A

High velocity signal void,

Flow-related enhancement

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6
Q

Flow affects image quality. (T or F)

A

True

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7
Q

Which artifact is produced as a result of motion of flowing nuclei?

A

Phase ghosting

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8
Q

two main uses of spatial pre-saturation

A

Chemical Pre-saturation

SPIR

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9
Q

Even echo rephasing reduces intra-voxel dephasing (T or F)

A

True

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10
Q

Another term for time of flight is inflow effect. (T or F)

A

False
Another term for entry slice phenomenon is inflow effect, as it is most prominent in the first slice of a ‘stack’ of slices.

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11
Q

Any tissue can be nulled as long as an RF pulse matching its precessional frequency is applied to the imaging volume before excitation. (T or F)

A

True

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12
Q

Pre-saturation techniques increase the RF deposition to the patient. (T or F)

A

True

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13
Q

STIR is most useful in post contrast imaging. (T or F)

A

False

In STIR sequences, gadolinium may be nulled along with fat, as gadolinium shortens the T1 recovery time of tissues taking up contrast to that of fat. Therefore, STIR sequences must never be used after giving gadolinium

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14
Q

Vortex

A

initially laminar but then passes thru a stenosis

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15
Q

laminar

A

different but consistent velocities

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16
Q

turbulent

A

different velocities that changes randomly

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17
Q

Counter current flow occurs when flowing nuclei are traveling in the same direction as slice selection. (T or F)

A

False

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18
Q

Which type of motion can we compensate for in MRI?

A

First order laminar flow

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19
Q

Determine which of the following parameters would result in the most entry slice phenomenon (i.e. entry slice phenomenon would increase compared to the other options).

A

Slice 1 of 20, 3000 TR, .7 mm slice thickness

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20
Q

Intra-voxel dephasing results in an increase in total signal amplitude from the voxel (T or F)

A

False

If a flowing nucleus is adjacent to a stationary nucleus in a voxel, there is a phase difference between the two nuclei. Therefore the nuclei within the same voxel are out of phase with each other, which results in a REDUCTION in total signal amplitude from the voxel

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21
Q

In a dual echo sequence, which of the following combinations would result in reduced flow artifact in the second echo?

A

TE 40 and 80 ms

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22
Q

As velocity of flow decreases, the time of flight effect decreases. (T or F)

A

True- This is called flow-related enhancement. See page 202 in the text for more information

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23
Q

What is the chemical shift at 1.5 T?

A

220 Hz

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24
Q

What is the name of the artifact that is produced as a result of motion of flowing nuclei?

A

phase ghosting

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25
Q

TOF

A

flowing nuclei in the slice may have excited before being rephased

26
Q

ESP

A

stationary nuclei become saturated.

27
Q

what result in a dark vessel

A

TOF

28
Q

What does TOF depend on

A

velocity of flow

TE

slice thickness

29
Q

chemical shift for 1T

A

147 Hz

30
Q

chemical shift for 1.5 T

A

220 Hz

31
Q

chemical shift for 3 T

A

441 Hz

32
Q

Which of the following will increase entry slice phenomenon

A

first slice of stack, long TR, thin slices, with counter current flow

33
Q

check q 6 on study guide

A

_

34
Q

TRUE or FALSE: A thinner slice is more likely to produce a signal void.

A

True

35
Q

During which would Entry-Slice Phenomenon increase

A

first slice in stack, thin slices, with fast flow, with long TR

36
Q

TOF phenomenon results in a dark vessel. (T or F)

A

True- a dark vessel because nuclei that were present during the excitation are usually not present when the rephasing pulse is delivered and vice versa.

37
Q

The frequency difference between fat and water is called ___________ and can be used to specifically null the signal from either fat or water.

A

Chemical Shift

38
Q

Which factors affect the magnitude of entry slice phenomenon

A

TR, slice thickness, velocity of flow, direction of flow

39
Q

To produce a signal, a nucleus must receive an excitation pulse and a rephasing pulse. If the nucleus is flowing, it may receive only the excitation pulse or the rephasing pulse, it will not produce a signal.

What does this most likely describe?

A

Time of Flight

40
Q

intravoxel dephasing

A

reduction from amplitude from the voxel

41
Q

entry slice phenonenom

A

aka inflow effect

42
Q

co current flow

A

flow in same direction

43
Q

counter current flow

A

flow in opposite directions

44
Q

chemical shift

A

frequency diff between fat and water

45
Q

fat sat

A

pre sat pulse precessional frequency of fat

46
Q

water sat

A

pre sat pulse at precessional frequency of water

47
Q

even echo rephasing

A

reduces intravoxel dephasing in dual echo when second echo is at multiple of the first

48
Q

Which of the following are true concerning pre-saturation?

A

uses additional RF to null signal from flowing nuclei

gives flowing nuclei a signal void

increases the RF deposition of the patient

49
Q

spatial presaturation

A

nullifies the signal from flowing nuclei to minimize the effects of TOF and ESP

50
Q

even echo rephasing

A

uses balanced echoes, demonstrates less dephasing than old echoes

51
Q

gradient moment rephasing

A

uses additional gradients to correct altered phase values

52
Q

Determine which of the following parameters would result in the most entry slice phenomenon (i.e. entry slice phenomenon would increase compared to the other options).

A

Slice 1 of 20, 3000 TR, .7 mm slice thickness

53
Q

Stationary nuclei always receive both excitation and rephasing pulses, but flowing nuclei present in the slice for the excitation may have exited the slice before rephasing. This is called ______________.

A

Time of Flight Phenomenon

54
Q

two main uses of spatial pre-saturation

A

Chemical Pre-saturation

SPIR

55
Q

STIR

A

never used after gad

56
Q

SPIR

A

may be used to null fat after gad

57
Q

Which type of motion can we compensate for in MRI

A

First order laminar flow

58
Q

TRUE or FALSE: Silicone may be saturated to null its signal in breast imaging.

A

true

59
Q

result of velocity increases, TOF increases

A

high velocity signal loss

60
Q

result of velocity decreases, TOF decreases

A

flow related enhancement

61
Q

Which type of flow can be compensated for?

A

first-order motion, laminar flow

62
Q

What does this describe?

Each slice is selectively excited by the RF pulse, but the rephasing gradient is applied to the whole body. A flowing nucleus that receives an excitation pulse is rephased regardless of its slice position and produces a signal.

A

TOF in gradient echo

Physics (15 decks)

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