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Study questions Flashcards

1
Q

Which material is commonly used for passive magnetic shielding within the walls of the MRI room?

A

Iron

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2
Q

For adults, what is the current FDA guideline limit for exposure to a magnetic field?

A

8 Tesla

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3
Q

For infants less than one month, what is the current FDA guideline limit for exposure to a magnetic field?

A

4 Tesla

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4
Q

What material is used for RF shielding?

A

Copper

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5
Q

The FDA guideline limits SAR for the head to

A

3.2 W/k

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6
Q

The FDA guideline limits SAR averaged over the whole body to:

A

4.0 W/kg

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7
Q

The normal operating mode with limit to the whole body SAR average to no greater than:

A

2.0 W/kg

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8
Q

Increasing the flip angle from 45 degrees to 90 degrees will increase SAR by a factor of:

A

4

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9
Q

Which sequence is of most concern with regard to SAR?

A

Fast Spin Echo

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10
Q

The magnetic field of the hydrogen proton is known as:

A

The magnetic moment

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11
Q

Hydrogen protons in the low energy spin state are said to have their magnetic moment:

A

Aligned with the direction of the external magnetic field.

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12
Q

Within a few seconds of being placed in a magnetic field, the hydrogen protons reach a condition known as:

A

Thermal equilibrium

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13
Q

Properties of T2 relaxation

A

Spin-Spin
Exchange of energy among spins
63% decay transverse magnetization

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14
Q

Properties of T1 relaxation

A

Spin-Lattice
Spins give up/lose energy
63% of longitudinal magnetization has recovered

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15
Q

T2 relaxation times are mostly expressed in:

A

Milliseconds

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16
Q

Increasing the flip angle from 90 to 180 degrees requires how much of an increase in RF power?

A

4 times

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17
Q

T1 parameters for TR and TE

A

TR: 400-700 ms
TE: 25ms or less

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18
Q

T2 parameters for TR and TE

A

TR: 3000ms or higher
TE: 80-120 ms

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19
Q

Proton Density parameters for TR and TE

A

TR: 3000ms or higher
TE: 25ms or less

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20
Q

To obtain a TE which is “out of phase”, which type of pulse sequence would be selected?

A

Gradient echo

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21
Q

Ina gradient echo sequence, T1 weighting can be controlled by:

A

Both flip angle and TR

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22
Q

To produce a T1 weighted image using an extremely short TR, which gradient echo sequences would be selected?

A

Spoiled gradient echo

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23
Q

Decreasing flip angle does what to saturation

A

Decreased FA=Decreased saturation

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24
Q

The Maine function of Fourier transform in MR image reconstruction is to:

A

Convert time domain to frequency domain

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25
Q

Slice thickness is affected by the ____ of the slice selecting gradient.

A

Amplitude

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26
Q

What also affects slice thickness besides amplitude?

A

Transmit Bandwidth

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27
Q

Increasing which of the following will result in a direct increase in scan time?
A.Frequency matrix
B. Slice thickness
C.Phase matrix
D. Transmit bandwidth

A

Phase matrix

28
Q

Increasing the NSA results in:

A

Reduction in noise

29
Q

With regard to raw data, the data points which provide the greatest signal contribution are:

A

Low frequencies

30
Q

Where in k-space is high frequency data?

A

Outer

31
Q

With regard to raw data, edge detail is provided by

A

high frequencies

32
Q

In a 3D FFT acquisition, SNR is proportional to

A

The square root of the number of slices.

33
Q

Reformatting image data into another plane is done through a process known as

A

MPR

34
Q

Which scan time reduction technique may require a reference or calibration scan prior to the actual acquisition?

A

Parallel Imaging

35
Q

Spin Echo EPI is most often used to acquire which type of MR studies?

A

Diffusion weighted images

36
Q

Decreasing matrix size does what to distortion artifacts?

A

Decreasing matrix=Decreased distortion artifacts

37
Q

When each gradient is applied:
Slice selection
Phase Encoding
Frequency encoding

A

Slice-During RF pulse
Phase-During FID
Frequency-During sampling of echo

38
Q
A
39
Q

Low frequencies=
? Signal
? Contrast

A

Low Frequency =
High Signal
High Contrast

40
Q

High frequencies=
? Signal
? Edge Detail
? Noise

A

High Frequency=
Low Signal
High Edge detail
High Noise

41
Q

Sense vs. Smash Technique

A

Sense-Utilizes calibration technique
Smash-Utilizes data from raw scan to reconstruct image (no calibration scan)

42
Q

Half Fourier or Partial Fourier does what to spatial resolution and noise

A

Spatial Resolution not affected
Noise is increased

43
Q

Reducing TR = ? Saturation

A

Reducing TR = Increase in saturation ( Less signal-Not enough time to recover)

44
Q

Following the injection of gad, which technique is not recommended?

A

STIR

45
Q

Which technique of fat suppression can be successfully utilized at all field strengths following the injection of gad?

A

Dixon Method

46
Q

Reducing the slice thickness by a factor of 2, will reduce the voxel volume by a factor of

A

2

47
Q

Reducing the FOV by a factor of 2 will reduce the voxel volume by a factor of

A

4

48
Q

Truncation artifact can be reduced by

A

Increasing the number of high frequency samples

49
Q

Utilizing a gradient echo sequence, which parameter is adjusted to produce an out of phase image?

A

TE

50
Q

Chemical shift is seen along which direction?

A

Frequency encoding direction

51
Q

To reduce magnetic susceptibility, do what to receiver bandwidth?

A

Increase receiver bandwidth to decrease magnetic susceptibility

52
Q

Increase FOV 2 =
?Signal
?Noise

A

Increase FOV 2=
Increase Signal 4
-Noise

53
Q

Increase Slice thickness 2=
?Signal
?Noise

A

Increase Slice thickness 2=
Increase Signal 2
-Noise

54
Q

Increase NSA 2=
?Signal
?Noise

A

Increase NSA 2=
-Signal
Decrease Noise sq root 2

55
Q

Increase Receiver Bandwidth 2=
?Signal
?Noise

A

Increase Receiver Bandwidth 2=
-Signal
Increase Noise sq root 2

56
Q

In a spin echo, normal flow will appear as:

A

A Signal Void

57
Q

In a gradient echo, normal flow will appear as:

A

High signal

58
Q

The contrast mechanism for time of flight is

A

Flow related enhancement

59
Q

2D TOF TR and Flip angle

A

Short TR and high flip angle

60
Q

Optimum signal due to flow is achieved when the blood flow is

A

Perpendicular to the slice plane

61
Q

Name the disadvantage of 3D TOF

A

Best for imaging slow flow

62
Q

Advantage of 2D TOF

A

Larger Voxel Volumes lead to large coverage

63
Q

The contrast mechanism for phase contrast MRA is:

A

Velocity induced phase shifts

64
Q

Which pulse sequence is commonly utilized for CE-MRA?

A

Spoiled Gradient Echo

65
Q

Which pulse sequence is most commonly used for Diffusion?

A

Spin Echo EPI

66
Q

Which sequence is most commonly used to acquire a perfusion study utilizing a bolus of gad?

A

gradient echo EPI

MRI (3 decks)

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