99. MRI: CONVENTIONAL SPIN ECHO Flashcards
1
Q
- What aspects define a Pulse Sequence?
A
- A series of Radio Frequency Pulses
- Gradient Applications
- Intervening Time Periods
2
Q
- 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
3
Q
- What happens when we select intervening time periods?
A
- we control the image weighting
4
Q
- 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
5
Q
- What are the Repetition and Echo Times needed to produce T1 images?
A
- short repetition time
- short echo time
6
Q
- What are the Repetition and Echo Times needed to produce T2 images?
A
- long repetition time
- long echo time
7
Q
- What are the Repetition and Echo Times needed to produce Proton Density Images?
A
- long repetition time
- short echo time
8
Q
- 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
9
Q
- Label the image.
A
- Net Magnetisation Vector
- Net Magnetisation Vector flipped into the Transverse
Plane - The Net Magnetisation Vector starts dephasing
between 90° and 180 °
- the signal at this point is low - This is what marks the beginning of the rephasing the
Net Magnetisation Vector - 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
10
Q
- What is the Spin Echo?
A
- this is the region between the 180° Signal pulse to the
next 90° Signal Pulse
11
Q
- 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
12
Q
- 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
13
Q
- What is the effect of Rephasing?
A
- the signal in the Receiver Coil is regenerated
- this signal can now be measured again
14
Q
- 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
15
Q
- What happens when we rephase the Net Magnetisation Vector?
A
- we eliminate the effect of the Magnetic Field
inhomogenities
16
Q
- How do we produce a T1 Weighted Set of images?
A
- A CONVENTIONAL SPIN ECHO
- is used for this process - 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 - THE RADIO FREQUENCY PULSE AT 180°
- rephases the Net Magnetisation Vector
- this produces the image
- THE ECHO TIME
- is short
- THE REPETITION TIME
- is short
17
Q
- How do we produce a T2 Weighted Set of images?
A
- A CONVENTIONAL SPIN EHCO
- is used for this process - A DUAL ECHO SEQUENCE
- consists of two 180° pulses
- these are applied to the signal
- they produce two spin echoes - 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 - THE REPETITION TIME LOOKS AT THE:
- distance between the first 90° pulse to the second
90° pulse - THE T2 IMAGE IS OBTAINED THROUGH:
- a long echo time
- a long repetition time - THE PROTON DENSITY IMAGE IS OBTAINED
THROUGH:
- a short echo time
- a long repetition time
18
Q
- 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
- 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
- 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
- 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
- Define: Fast Spin Echo (FSE) Sequences.
A
- they are a much faster version of the Conventional
Spin Echo
23
Q
- What do Fast Spin Echo Sequences make use of?
A
- they use multiple 180° rephasing pulses
- each one produces a spin echo
24
Q
- 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
- Define: Echo Spacing.
A
- this is the space between each Echo
26
Q
- How many 180° Radio Frequency pulses are applied during every Repetition Time?
A
- 2 to 30 pulses
27
Q
- 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
- 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
- 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
- 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
- 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
- What do we use Fast Spin Echo Sequences to image?
A
THEY IMAGE:
- brains
- spines
- joints
- extremities
- the pelvis
