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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
Concerning T1 weighting, what if too long?
no differences between fat and water demonstrated
26
Which describes a spin echo?
90-degree excitation pulse followed by 180-degree rephasing pulse
27
___: number of mobile hydrogen protons per unit volume of that tissue.
proton density
28
Concerning T1 and T2 weighting, what controls the amount of T1 weighting?
TR
29
Concerning T1 and T2 weighting, for a T1 weighted image ...
TR must be short
30
Concerning T1 and T2 weighting, what controls the amount of T2 weighting?
TE
31
Concerning T1 and T2 weighting, for a T2 weighted image ...
TE must be long
32
What is T1 Relaxation?
Regained in the longitudinal plane. Aka: spin lattice
33
What is T2 Decay?
Lost in the transverse plane. Aka: spin-spin
34
What is the description of TR?
time between each 90-degree exitation pulse
35
What is the description of TE?
time between the 90-degree excitation pulse and the peak of the spin echo
36
What is the description of TAU?
1/2 TE
37
What is the T2 time of fat?
short T2 time
38
What is the T2 time of water?
long T2 time
39
Intrinsic factors
Inherent to the body's tissues. Cannot be changed.
40
Extrinistic factors
Set by the technologist. Can be changed.
41
How do we adjust TR and TE to achieve a PD-weighted image?
long TR and short TE
42
What are inhomogeneities?
areas that do not match the external field strength
43
___: the basic MRI contrast
PD
44
Match high signal and low signal image characteristics ... white on the image
areas of high signal
45
Match high signal and low signal image characteristics ... dark on the image
areas of low signal
46
Match high signal and low signal image characteristics ... gray on the image
areas of intermediate signal
47
Match the examples of intrinsic and extrinsic contrast parameters ... T1 recovery time, T2 decay time, PD, flow, ADC
Intrinsic
48
Match the examples of intrinsic and extrinsic contrast parameters ... TR, TE, flip angle, TI, turbo factor/ETL, B-value
Extrinsic
49
What are the 3 factors that T1 and T2 relaxation depend on? Choose all that apply ...
* inherent energy of the tissue * how closely packed the molecules are * how well the molecular tumbling rate matches the Larmor frequency of H
50
How do gradients affect the main magnetic field? (Select all that apply)
* 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
Choose extrinsic contrast parameters from the list below.
* TR * Flip Angle * TE
52
Which of the following best describes a T1 weighted image? (Select all that apply)
* Bright fat | * Dark Water
53
Which of the following controls T2* weighting in gradient echo?
TE
54
What is the approximate T1 relaxation time of water at 1T?
2500 ms
55
The spin echo is created by:
A 180 degree RF pulse
56
For T2 weighting, the TE must be _____.
long
57
Intrinsic parameters are those that cannot be changed because they are inherent to the body's tissues.
True
58
T2* decay is faster than T2 decay since it is a combination of which of the following effects?
* T2 decay itself | * Dephasing due to magnetic field inhomogeneities
59
What controls the polarity of a gradient?
The direction of the current through the gradient coil
60
Saturation results in T1 weighting because:
Vectors are pushed beyond the transverse plane as they were incompletely recovered before the RF excitation pulse
61
To achieve T1 weighting in gradient echo sequences, the flip angle should be ______.
Large
62
Which of the following controls T1 weighting in gradient echo?
TR and flip angle | See page 52 in the text.
63
TR controls T2 weighting.
False | TR controls the amount of T1 weighting.
64
Which of the following items are T1 and T2 relaxation times dependent on? (hint: there are three)
* 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
The TE is twice the TAU.
True
66
Rewinders are gradients that rephase.
True
67
Gradients that dephase are called __________.
spoilers
68
Gradients are used to rephase spins in gradient echo sequences because:
They are faster to apply than an RF pulse | See pages 50-51 in the text.
69
Inhomogeneities are areas within the magnetic field that do not exactly match the external magnetic field strength.
True
70
Spin echo sequences do not compensate for magnetic field inhomogeneities, while gradient echo sequences do compensate for magnetic field inhomogeneities.
False
71
Generally speaking, gradient echo sequences are faster than spin echo sequences.
True
72
___ controls the amount of T1 weighting.
TR
73
Which of the following is known as the basic MRI contrast?
Proton density weighting
74
What are the two extremes of contrast in MRI?
Fat
75
Which of the following statements is true:
pin-spin interactions drive T2 contrast | Review pages 23-25 in the text.
76
For PD weighting, the TR must be ______.
Long

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