101. MRI: GRADIENT ECHO SEQUENCE

Question 1

1. Define: Gradient Echo Pulse Sequences.

Answer 1

• they are sequences
• they use a gradient to reduce the magnetic
  inhomogeneity effects

THIS IS DIFFERENT FROM THE:
- 180° Radio Frequency Pulses that are used in the
Conventional and Turbo Spin Echo sequences

Question 2

2. Other than the gradient, what else do the Gradient Echo Sequences make use of in order to reduce the magnetic inhomogeneity effects?

Answer 2

• they use a variable flip angle
• this is usually less than 90°
• this allows for short scan times
• they do not refocus the magnetic field inhomogenities

Question 3

3. What kind of images do the Gradient Echo Sequences produce?

Answer 3

• they produce T2* Weighted Images
• they have long Echo Times (TE)

Question 4

4. What is the Rephasing Mechanism of Spin Echo (Conventional or Turbo) Sequences?

Answer 4

• the Radio Frequency Pulse

Question 5

5. What is the Rephasing Mechanism of Gradient Echo Sequences?

Answer 5

• different gradients

Question 6

6. What is the Flip Angle of Spin Echo (Conventional or Turbo) Sequences?

Answer 6

• the 90° angle

Question 7

7. What is the Flip Angle of Gradient Echo Sequences?

Answer 7

• it varies
• it is usually less than 90°

Question 8

8. How efficient is the Spin Echo (Conventional or Turbo) Sequence at reducing the magnetic inhomogeneity?

Answer 8

• it is very efficient
• it has true T2 weighted images

Question 9

9. How efficient is the Gradient Echo Sequence at reducing the magnetic inhomogeneity?

Answer 9

• it is not very efficient
• it has T2* weighted images

Question 10

10. What is the acquisition time of an image when we use the Spin Echo (Conventional or Turbo) Sequence?

Answer 10

• it is long
• this is a slow sequence

Question 11

11. What is the acquisition time of an image when we use the Gradient Echo Sequence?

Answer 11

• it is short
• this is a fast sequence

Question 12

12. What are the two types of Gradient Echo Sequences?

Answer 12

1. Spoiled (Incoherent) Gradient Echo Sequences
2. State (Coherent) Gradient Echo Sequences

Question 13

13. What determines the type of Gradient Echo sequence we will have?

Answer 13

• it is determined by what happens to the Residual
  Transverse Magnetisation (TM)
• this will occur after the signal in each Repetition Time
  has ben received

Question 14

14. Define: Spoiled (Incoherent) Gradient Echo Sequences.

Answer 14

• the Residual Transverse Magnetisation (TM) is
  destroyed
• it does not interfere with the next Repetition Time (TR)

Question 15

15. Define: State (Coherent) Gradient Echo Sequences.

Answer 15

• the Residual Transverse Magnetisation (TM) is not
  destroyed
• it does interfere with the next Repetition Time (TR)

Question 16

16. When do we usually use T2* Weighted images?

Answer 16

• we use them when a high signal intensity is required
  from water

Question 17

17. What body parts do we capture using T2* Weighted Images?

Answer 17

1. White Blood Cardiac Images
2. Spinal Images
3. Joint Images