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MRI > Week 5 > Flashcards

Week 5 Flashcards

1
Q

What is a pulse sequence in MRI?

A

The process of acquiring image data by disorienting net magnetization with RF pulses

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2
Q

What are the four types of traditional Pulse sequences?

A
  1. Spin echo (SE)
  2. Inversion recovery (IR)
  3. Gradient echo (GE)
  4. Echo planar imaging (EPI)
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3
Q

The pulse sequence is represented by a timing diagram that details the RF pulse and gradient variation events. What are the five events recorded in a pulse sequence timing diagram?

A
  1. RF transmission (RF-t)
  2. RF receive (RF-t)
  3. Slice select
  4. Readout
  5. Phase
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4
Q

What is Echo time (TE)?

A

The time it takes to complete an entire sequence

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5
Q

What is TE measured in?

A

Milliseconds (ms)

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6
Q

What interval denotes 1 full TE period?

A

From the 90° pulse all the way to the resulting echo

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7
Q

In the pulse sequence timing diagram, the interval from the 90° pulse to the 180° pulse would represent how much of a TE period?

A

Half of 1 TE period

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8
Q

What happens during the first event of the timing diagram, RF-t?

A

An RF pulse flips net magnetization into the transverse direction

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9
Q

What is another term for the RF transmit event?

A

Excitation event

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10
Q

The excitation event always begins with a 90° initial pulse, followed by 180° pulse. True or false?

A

False; it normally is, but could also be a flip angle

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11
Q

Once net magnetization is flipped during RF-t, what happens during the second event (RF-r)?

A

The signal created by the relaxing magnetization immediately begins to weaken.

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12
Q

The “Dephasing event” is another term used for which event?

A

The second event, RF-receive

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13
Q

Explain what free induction decay (FID) refers to.

A

The signal that’s produced by the protons during the relaxation/dephasing process.
*Remember, T2 relaxation and amplitude

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14
Q

When does the third event, slice select, take place?

A

Slice selection occurs during the first event, RT-t

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15
Q

The slice select event allows for a specific slice to be singled out in the body on the chosen plane (sagittal, coronal, axial). What is this phenomena known as?

A

Spatial localization

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16
Q

How many times does the fourth event occur?

A
  1. the readout gradient is active during RF-t, RF-r, and slice selection.
  2. Turns on again during the resultant echo
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17
Q

What does the readout gradient do while it’s active?

A

It’s samples the signal produced by the excitation event, dephasing event, and any subsequent echoes.

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18
Q

The readout gradient samples the signals produced. What is this process called?

A

Frequency encoding

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19
Q

When does the fifth event occur?

A

The phase gradient is active between the 90° and 180° pulse

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20
Q

What is the phase gradient determined by?

A

The number of phase encoding lines in a slice

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21
Q

What are the two types of spin echo pulse sequences?

A
  1. Conventional spin echo (CSE)
  2. Fast spin Echo (FSE)
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22
Q

Conventional spin echoes can be T1 weighted, T2 weighted, or proton density weighted. True or false?

A

True

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23
Q

Conventional spin echo pulse sequences are traditional and basic. When are they utilized?

A

Never, obsolete

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24
Q

How many echoes are contained per one single TE period in a CSE? How does this affect scan time?

A

One; very long scan times.

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25
Q

FSEs are significantly faster that CSEs. Why?

A

Because of their added echo train length.

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26
Q

Fast spin echo pulse sequences can be T1 or T2 weighted, but not proton density weighted. True or false?

A

False; similar to conventional, FSEs can be T1, T2, or PD weighted.

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27
Q

What makes an inversion recovery pulse sequence different than a spin echo sequence?

A

IR contains an additional 180° pulse before the initial 90° pulse

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28
Q

What does inversion time (TI) refer to?

A

The time between the pre-180° pulse to the 90° pulse during an inversion recovery pulse sequence

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29
Q

Approximately how long are inversion times during STIR imaging?

A

100-150 ms

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30
Q

Longer inversion times will result in the suppression of what tissue type?

A

Fat

31
Q

When a certain tissue type is suppressed, how does its appearance change on the MRI image?

A

Suppressed tissues appear darker

32
Q

If we recall the appearance of different tissues during T1 relaxation (week 4), what would happen to T1 contrast if the inversion time is increased? Why?

A

Decrease; Long TI times suppress fat, suppressed fat appears dark - just like water.

33
Q

What is the purpose of the pre-180° pulse during IR?

A

The pre-pulse establishes T1 relaxation and contrast before the pulse sequence even begins.

34
Q

What are the two types of inversion recovery Pulse sequences?

A
  1. Short time inversion recovery (STIR)
  2. Fluid attenuated inversion recovery (FLAIR)
35
Q

What kind of technique is STIR imaging?

A

Fat suppression technique

36
Q

IV Gadolinium contrast cannot be used during STIR imaging due to its appearance being too similar to fat on images. True or false?

A

True

37
Q

Describe the characteristics of an image obtained via STIR

A

All anatomy with a high fat content, like bone, tendon, and muscle, will appear very dark. This results in water content appearing highlighted - blood, edema, and infection.

38
Q

What type of technique is FLAIR imaging?

A

A cerebral spinal fluid (CSF) suppression technique

39
Q

Approximately how long are inversion times in FLAIR imaging?

A

About 2000 ms

40
Q

How do FLAIR imaging TIs and TRs compared to STIR?

A

FLAIR has longer TI and TR times.

41
Q

Describe the characteristics of an image obtained via FLAIR.

A

All fluid in the image will be suppressed, resulting in enhancement of fat containing tissues and their potential pathology

42
Q

What are the four types of gradient echo pulse sequences?

A
  1. Gradient recall echo (GRE)
  2. Spoiled gradient echo (SPGE)
  3. Steady state gradient echo (SSGE)
  4. Fast gradient recall echo (FGRE)
43
Q

What 3 tissues would be best displayed during a GRE pulse sequence?

A
  1. Blood in the brain
  2. Ligaments
  3. Cartilage
44
Q

What is the purpose of a spoiler pulse during a spoiler gradient echo pulse sequence?

A

To terminate any remaining magnetization

45
Q

During an SPGE, when is the spoiler pulse emitted?

A

After the third event, readout gradient

46
Q

What two things could spoiler pulse be?

A
  1. A strong radio frequency pulse
  2. A strong gradient pulse
47
Q

What’s the difference between a radio frequency pulse and a gradient pulse?

A

An RF pulse changes the direction of hydrogen atoms in the body from the longitudinal to the transverse plane. A gradient pulse causes positive and negative variations to the magnetic field.

48
Q

Which gradient echo pulse sequence preserves remaining magnetization by rephasing it?

A

Steady state gradient echo (SSGE)

49
Q

How does rephasing preserve magnetization?

A

By allowing both the relaxed protons and the remaining magnetization to be present for the next RF flip angle.

50
Q

What kind of images are created as a result of rephasing?

A

T2* weighted images

51
Q

What three facts make GRE sequences unique from SE and IR?

A
  1. SE and IR use a 90° RF pulse to initiate the sequence (not counting IR’s pre-180°). GRE uses a smaller flip angle.
  2. GRE uses a gradient pulse for refocusing, not a 180° RF pulse.
  3. GR
52
Q

What kind of pulse is used to result in a T1 weighted FGE?

A

A 180° RF pulse

53
Q

What kind of pulse is used to result in a T2 weighted FGE?

A

A 90°-180°-90° RF pulse combo

54
Q

Why are the RF pulses/pulse used before the initial flip angle during a fast gradient echo pulse sequence?

A

To establish different types of contrast: T1 weighted, or T2 weighted

55
Q

At the end of an FGE pulse sequence, a spoiler is used to_______ the relaxation process

A

Accelerate

56
Q

What are the three requirements for a FGE?

A
  1. Short TR.
  2. Short TE
  3. Small flip angle
57
Q

Which type of gradient echo pulse sequence is the fastest and loudest technique?

A

Echo planar imaging (EPI)

58
Q

EPI sequences can acquire larger amounts of gradient echoes per TR cycle. How does it achieve this?

A

By alternating the readout gradient and phase collection

59
Q

This diagram displays which event during the pulse sequence?

A

First event; RF-transmit

60
Q

This diagram displays which event during the pulse sequence?

A

Second; RF-receive

61
Q

What event of the pulse sequence is displayed by the diagram?

A

Third event; slice select gradient

62
Q

Which event of the pulse sequence is displayed by the diagram?

A

Fourth event; readout gradient

63
Q

Which event of the pulse sequence is displayed by the diagram?

A

Fifth event; phase gradient

64
Q

Which pulse sequence is displayed by the diagram?

A

Conventional spin echo

65
Q

Which pulse sequence is displayed by the diagram?

A

Fast spin echo

66
Q

Which inversion recovery pulse sequence is displayed by the diagram?

A

Short time inversion recovery; STIR

67
Q

Which inversion recovery pulse sequences displayed by the diagram?

A

Fluid attenuated inversion recovery; FLAIR

68
Q

Which of the four gradient echo pulse sequences is displayed by the diagram?

A

Gradient recall echo; GRE

69
Q

Which of the four gradient echo pulse sequences is displayed by the diagram?

A

Spoiler gradient echo; SPGE

70
Q

Which of the four gradient echo pulse sequences is displayed by the diagram?

A

Steady state gradient echo; SSGE

71
Q

Which of the four gradient echo pulse sequences is displayed by the diagram?

A

Fast gradient echo; FGE

72
Q

Which of the four pulse sequence types is displayed by the diagram?

A

Echo planar imaging; EPI

73
Q

This is an example of an image acquired via what specific pulse sequence?

A

STIR

74
Q

This is an example of an image acquired with what specific pulse sequence?

A

FLAIR

MRI (11 decks)

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