93. MRI: CONTRAST

Question 1

1. Why does an image have Contrast?

Answer 1

• it has contrast if there are areas of high signals
• and if there are areas of low signals
• this is what creates the difference between the
  brightness and darkness areas

Question 2

2. How is the Net Magnetisation Vector separated?

Answer 2

• it is separated into the individual vectors
• these are the vectors of the tissues that are present in
  the patient

Question 3

3. What are some examples of these tissues?

Answer 3

1. Fat
2. Cerebro-Spinal Fluid (CSF)
3. Muscles

Question 4

4. What can be said about a tissue with a high signal?

Answer 4

• it will come across as White in the image
• it has a large Transverse Component of Magnetisation

Question 5

5. What can be said about a tissue with an intermediate signal?

Answer 5

• it will come across as Grey in the image
• it has a Medium Transverse Component of
  Magnetisation

Question 6

6. What can be said about a tissue with a low signal?

Answer 6

• it will come across as Black in the image
• it has a Small Transverse Component of Magnetisation

Question 7

7. What parameters control Image Contrast?

Answer 7

1. Repetition Time (RT)
2. Echo Time (TE)
3. Flip Angle
4. Turbo-Factor (TF)
   
   • this is also known as the Echo Train Length (ETL)
5. B Value

Question 8

8. Define: Repetition Time (TR).

Answer 8

• this is the time it takes for the application of one Radio
  Frequency Pulse
• to the application of the next Radio Frequency Pulse

Question 9

9. Define: Echo Time (TE).

Answer 9

• this is the time between the Radio Frequency Excitation
  Pulse
• and the point at which the Signal is collected

Question 10

10. Define: Flip Angle.

Answer 10

• this is the angle at which the Net Magnetisation Vector
  is moved to
• this is a result of the Radio Frequency Excitation

Question 11

11. Define: Turbo Factor (TF)
    : Echo Train Length (ETL)

Answer 11

• this is the number of 180° radio Frequency Pulses
• and their resultant Echoes

Question 12

12. Define: Time from Inversion (TI).

Answer 12

• this is the Inversion Recovery time
• it is how long it takes to get from 180° back to 90°

Question 13

13. Define: B-Value.

Answer 13

• this is used in weighted Diffusion

Question 14

14. Who controls the Contrast Parameters?

Answer 14

• the System Operator
• they cannot control all the parameters
• the parameters they use depends on the type of tissue

Question 15

15. What other kinds of parameters can we come across?

Answer 15

• there are parameters that are inherent to the Tissue
• these affect the Contrast
• they are not controlled by the System Operator

Question 16

16. What are the tissue Inherent Parameters?

Answer 16

1. T1 Recovery
2. T2 decay
3. Proton Density (PD)
4. Flow
5. Apparent Diffusion Coefficient (ADC)