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MED 107- MEDICAL PHYSICS II > 99. MRI: CONVENTIONAL SPIN ECHO > Flashcards

99. MRI: CONVENTIONAL SPIN ECHO Flashcards

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1
Q
  1. What aspects define a Pulse Sequence?
A
  1. A series of Radio Frequency Pulses
  2. Gradient Applications
  3. Intervening Time Periods
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2
Q
  1. What do Pulse Sequences control?
A
  • they control the way in which the system applies the
    Radio Frequency Pulses
  • they control the gradients applied

THEY ARE REQUIRED BECAUSE:
- they refocus the spins
- they allow for a sufficient signal to be produced
- this is what forms the image

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3
Q
  1. What happens when we select intervening time periods?
A
  • we control the image weighting
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4
Q
  1. What are Conventional Spin Echoes (SE / CSE) Pulse
    Sequences used for?
A
  • they are used to produce T1, T2 or Proton Density
    Weighted Images

THEY ARE ONE OF THE MOST BASIC PULSE SEQUENCES:
- that are used in MRI

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5
Q
  1. What are the Repetition and Echo Times needed to produce T1 images?
A
  • short repetition time
  • short echo time
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6
Q
  1. What are the Repetition and Echo Times needed to produce T2 images?
A
  • long repetition time
  • long echo time
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7
Q
  1. What are the Repetition and Echo Times needed to produce Proton Density Images?
A
  • long repetition time
  • short echo time
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8
Q
  1. What is the Pulse Sequence in Conventional Spin Echos?
A
  • there is a 90° Excitation Pulse
  • this is followed by a 180° Rephasing Pulse
  • this is followed by an Echo
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9
Q
  1. Label the image.
A
  1. Net Magnetisation Vector
  2. Net Magnetisation Vector flipped into the Transverse
    Plane
  3. The Net Magnetisation Vector starts dephasing
    between 90° and 180 °
    - the signal at this point is low
  4. This is what marks the beginning of the rephasing the
    Net Magnetisation Vector
  5. This is where the rephasing continues
    - the Net magnetisation Vector is rephased to face the
    opposite direction
    - there is an increase in the signal strength
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10
Q
  1. What is the Spin Echo?
A
  • this is the region between the 180° Signal pulse to the
    next 90° Signal Pulse
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11
Q
  1. What happens after the 90° Radio Frequency Pulse is applied?
A
  • the spins will lose their Precessional Coherence
  • the Net Magnetisation vector decays
  • it decays in the Transverse plane
  • it can no longer generate a signal
  • due to the MR active nuclei being dephased
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12
Q
  1. What is the purpose of the 180° Radio Frequency Pulse?
A
  • it is used to bring back the nuclei into phase
  • this is called Rephasing
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13
Q
  1. What is the effect of Rephasing?
A
  • the signal in the Receiver Coil is regenerated
  • this signal can now be measured again
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14
Q
  1. What is the name assigned to the regenerated signal?
A
  • this is called the Echo
  • a Radio Frequency Pulse was used to generate this
    signal
  • this means that it is actually called a Spin Echo
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15
Q
  1. What happens when we rephase the Net Magnetisation Vector?
A
  • we eliminate the effect of the Magnetic Field
    inhomogenities
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16
Q
  1. How do we produce a T1 Weighted Set of images?
A
  1. A CONVENTIONAL SPIN ECHO
    - is used for this process
  2. A SINGLE SPIN ECHO PULSE
    - consists of a single 180° Radio Frequency Pulse
    - this is applied after the Excitation Pulse
    - this is what produces the Single Spin Echo
  3. THE RADIO FREQUENCY PULSE AT 180°
    • rephases the Net Magnetisation Vector
    • this produces the image
  4. THE ECHO TIME
    • is short
  5. THE REPETITION TIME
    • is short
17
Q
  1. How do we produce a T2 Weighted Set of images?
A
  1. A CONVENTIONAL SPIN EHCO
    - is used for this process
  2. A DUAL ECHO SEQUENCE
    - consists of two 180° pulses
    - these are applied to the signal
    - they produce two spin echoes
  3. THIS KIND OF SEQUENCE
    - provides two images per slice location
    - one is a Proton Density Weighted Image
    - the other image is a T2 Weighted Image
  4. THE REPETITION TIME LOOKS AT THE:
    - distance between the first 90° pulse to the second
    90° pulse
  5. THE T2 IMAGE IS OBTAINED THROUGH:
    - a long echo time
    - a long repetition time
  6. THE PROTON DENSITY IMAGE IS OBTAINED
    THROUGH:
    - a short echo time
    - a long repetition time
18
Q
  1. What kind of standard are Conventional Spin Echo Sequences?
A
  • they are the Gold Standard
  • the contrast they produce is understood well
  • it is a predictable contrast
19
Q
  1. What do Conventional Spin Echo Sequences produce?
A
  • they produce T1 weighted images
  • they produce T2 weighted images
  • they produce Proton Density weighted images

ALL THESE IMAGES:
- are a good quality
- they can be used for any part of the body

20
Q
  1. Why is the application of Conventional Spin Echo Sequences limited in MRIs nowadays?
A
  • the Fast and Turbo Spin Echo Sequences are preferred
21
Q
  1. When do we still make use of Conventional Spin Echo Sequences?
A
  • we use them at 1.5 Teslas to produce T1 weighted
    images of the brain
22
Q
  1. Define: Fast Spin Echo (FSE) Sequences.
A
  • they are a much faster version of the Conventional
    Spin Echo
23
Q
  1. What do Fast Spin Echo Sequences make use of?
A
  • they use multiple 180° rephasing pulses
  • each one produces a spin echo
24
Q
  1. Define: Echo Train Length (ETL).
A
  • this is also known as the Turbo Factor
  • it is the number of 180° Radio Frequency pulses
  • it is the number of Resultant echoes
25
Q
  1. Define: Echo Spacing.
A
  • this is the space between each Echo
26
Q
  1. How many 180° Radio Frequency pulses are applied during every Repetition Time?
A
  • 2 to 30 pulses
27
Q
  1. What is the Turbo Factor in this image?
A
  • 8
  • there are eight 180° Radio Frequency Pulses in one
    Repetition Time
  • there are 8 Echoes
28
Q
  1. What are the effects of a Short Turbo Factor?
A
  • it decreases the effective Echo Time
  • this increases the T1 weighting
  • it increases the Scan Time
29
Q
  1. What are the effects of a Long Turbo Factor?
A
  • it increases the effective Echo Time
  • this increases the T2 weighting
  • it reduces the Scan Time
  • it increases the image blurring
30
Q
  1. Why does an increase in the Turbo Factor increase the image Blurring?
A
  • a greater number of echoes is obtained
  • at different Echo Times
  • from the same image
31
Q
  1. What does a Fast Spin Echo Sequence produce?
A
  • T1 Scans
  • T2 Scans
  • Proton Density Scans
  • all in a fraction of the time of a Conventional Spin Echo
32
Q
  1. What do we use Fast Spin Echo Sequences to image?
A

THEY IMAGE:
- brains
- spines
- joints
- extremities
- the pelvis

MED 107- MEDICAL PHYSICS II (108 decks)

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