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Physics > Chapter 2 > Flashcards

Chapter 2 Flashcards

1
Q

What are the characteristics of T1?

A

bright fat, dark water

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2
Q

What are the characteristics of T2?

A

bright water, dark fat

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3
Q

What are the characteristics of PD?

A

high proton density is bright, low proton density is dark

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4
Q

Concerning gradients, what are spoilers?

A

gradients that dephase

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5
Q

Concerning gradients, what are rewinders?

A

gradients that rephase

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6
Q

Concerning gradients, what is the advantage of gradients?

A

fast scan times

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7
Q

Concerning gradients, what is the disadvantage of gradients?

A

no compensation for magnetic field inhomogenities

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8
Q

What is the TR, TE and FA of T1?

A

short TR, short TE and large FA

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9
Q

What is the TR, TE and FA of T2?

A

long TR, long TE and small FA

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10
Q

What is the TR, TE and FA of PD?

A

long TR, short TE and small FA

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11
Q

___: variable excitation pulse (not just 90-degrees).

A

gradient

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12
Q

What is the description of fat molecules?

A

Slow molecular trumbling rate. Closely-packed molecules

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13
Q

What is the description of water molecules?

A

Fast molecular tumbling rate. Molecules are spaced apart

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14
Q

___: the decay of the FID following the RF excitation pulse.

A

T2

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15
Q

Images obtain contrast mainly through the mechanisms of …

  1. T1 Recovery
  2. T2 Decay
  3. Proton or Spin Density
A

1, 2 and 3

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16
Q

What is the typical value for a T1 sequence?

A

TR=300-700

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17
Q

What is the typical value for a T2 sequence?

A

TR=3000+

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18
Q

TRUE of FALSE: The T1 and T2 relaxation times, although inherent to that tissue, are dependent on the field strength of the magnet.

A

True

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19
Q

In general, what are the two extremes of contrast in MRI?

A

fat and water

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20
Q

Concerning T2 weighting, contrast depends predominately on …

A

T2 times between fat and water

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21
Q

Concerning T2 weighting, why long?

A

give fat and water time to decay

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22
Q

Concerning T2 weighting, if too short?

A

no differences in tissue demonstrated

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23
Q

Concerning T1 weighting, contrast depends predominately on …

A

the differences in the T1 times between fat and water

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24
Q

Concerning T1 weighting, why short?

A

neither fat nor water have sufficient time to return to Bo

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25
Q

Concerning T1 weighting, what if too long?

A

no differences between fat and water demonstrated

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26
Q

Which describes a spin echo?

A

90-degree excitation pulse followed by 180-degree rephasing pulse

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27
Q

___: number of mobile hydrogen protons per unit volume of that tissue.

A

proton density

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28
Q

Concerning T1 and T2 weighting, what controls the amount of T1 weighting?

A

TR

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29
Q

Concerning T1 and T2 weighting, for a T1 weighted image …

A

TR must be short

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30
Q

Concerning T1 and T2 weighting, what controls the amount of T2 weighting?

A

TE

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31
Q

Concerning T1 and T2 weighting, for a T2 weighted image …

A

TE must be long

32
Q

What is T1 Relaxation?

A

Regained in the longitudinal plane. Aka: spin lattice

33
Q

What is T2 Decay?

A

Lost in the transverse plane. Aka: spin-spin

34
Q

What is the description of TR?

A

time between each 90-degree exitation pulse

35
Q

What is the description of TE?

A

time between the 90-degree excitation pulse and the peak of the spin echo

36
Q

What is the description of TAU?

37
Q

What is the T2 time of fat?

A

short T2 time

38
Q

What is the T2 time of water?

A

long T2 time

39
Q

Intrinsic factors

A

Inherent to the body’s tissues. Cannot be changed.

40
Q

Extrinistic factors

A

Set by the technologist. Can be changed.

41
Q

How do we adjust TR and TE to achieve a PD-weighted image?

A

long TR and short TE

42
Q

What are inhomogeneities?

A

areas that do not match the external field strength

43
Q

___: the basic MRI contrast

44
Q

Match high signal and low signal image characteristics … white on the image

A

areas of high signal

45
Q

Match high signal and low signal image characteristics … dark on the image

A

areas of low signal

46
Q

Match high signal and low signal image characteristics … gray on the image

A

areas of intermediate signal

47
Q

Match the examples of intrinsic and extrinsic contrast parameters … T1 recovery time, T2 decay time, PD, flow, ADC

48
Q

Match the examples of intrinsic and extrinsic contrast parameters … TR, TE, flip angle, TI, turbo factor/ETL, B-value

49
Q

What are the 3 factors that T1 and T2 relaxation depend on? Choose all that apply …

A
  • inherent energy of the tissue
  • how closely packed the molecules are
  • how well the molecular tumbling rate matches the Larmor frequency of H
50
Q

How do gradients affect the main magnetic field? (Select all that apply)

A
  • They add to the main magnetic field
  • They subtract from the main magnetic field
  • They alter the main magnetic field in a linear fashion
51
Q

Choose extrinsic contrast parameters from the list below.

A
  • TR
  • Flip Angle
  • TE
52
Q

Which of the following best describes a T1 weighted image? (Select all that apply)

A
  • Bright fat

* Dark Water

53
Q

Which of the following controls T2* weighting in gradient echo?

54
Q

What is the approximate T1 relaxation time of water at 1T?

55
Q

The spin echo is created by:

A

A 180 degree RF pulse

56
Q

For T2 weighting, the TE must be _____.

57
Q

Intrinsic parameters are those that cannot be changed because they are inherent to the body’s tissues.

58
Q

T2* decay is faster than T2 decay since it is a combination of which of the following effects?

A
  • T2 decay itself

* Dephasing due to magnetic field inhomogeneities

59
Q

What controls the polarity of a gradient?

A

The direction of the current through the gradient coil

60
Q

Saturation results in T1 weighting because:

A

Vectors are pushed beyond the transverse plane as they were incompletely recovered before the RF excitation pulse

61
Q

To achieve T1 weighting in gradient echo sequences, the flip angle should be ______.

62
Q

Which of the following controls T1 weighting in gradient echo?

A

TR and flip angle

See page 52 in the text.

63
Q

TR controls T2 weighting.

A

False

TR controls the amount of T1 weighting.

64
Q

Which of the following items are T1 and T2 relaxation times dependent on? (hint: there are three)

A
  • How well the molecular tumbling rate matches the Larmor frequency of hydrogen
  • How closely packed the molecules are
  • The inherent energy of the tissue
65
Q

The TE is twice the TAU.

66
Q

Rewinders are gradients that rephase.

67
Q

Gradients that dephase are called __________.

68
Q

Gradients are used to rephase spins in gradient echo sequences because:

A

They are faster to apply than an RF pulse

See pages 50-51 in the text.

69
Q

Inhomogeneities are areas within the magnetic field that do not exactly match the external magnetic field strength.

70
Q

Spin echo sequences do not compensate for magnetic field inhomogeneities, while gradient echo sequences do compensate for magnetic field inhomogeneities.

71
Q

Generally speaking, gradient echo sequences are faster than spin echo sequences.

72
Q

___ controls the amount of T1 weighting.

73
Q

Which of the following is known as the basic MRI contrast?

A

Proton density weighting

74
Q

What are the two extremes of contrast in MRI?

75
Q

Which of the following statements is true:

A

pin-spin interactions drive T2 contrast

Review pages 23-25 in the text.

76
Q

For PD weighting, the TR must be ______.

Physics (15 decks)

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