89. MRI: SUPERCONDUCTING ELECTROMAGNETS

Question 1

1. What does this image show?

Answer 1

• this is a Superconductive MRI

Question 2

2. What do Superconductive MRIs make use of?

Answer 2

• they use a Solenoid Shaped coil

THIS IS MADE OF:
- alloys

Question 3

3. What are some examples of the alloys used in the Solenoid Shaped Coil made of?

Answer 3

1. Niobium or Titanium
2. Niobium or Tin
   - this is surrounded by Copper

Question 4

4. What are some properties of the alloys used in the Solenoid Shaped Coil?

Answer 4

1. THEY HAVE ZERO RESISTANCE TO ELECTRICAL
   CURRENT
   - this is only applicable when they are cooled down to
   about 10 Kelvin

NB:
- this means that there are no losses due to heat

Question 5

5. At what temperature do we keep the Solenoid-shaped Coil?

Answer 5

• we keep it at a temperature below Liquid Helium

Question 6

6. When looking at the Solenoid-shaped Coil, where does the current initially pass through?

Answer 6

• it initially passes through loops of wire
• these wires are made up of Niobium-Titanium Alloys

THIS CREATES:
- the magnetic field
- or it can bring the magnetic field up to strength

Question 7

7. What happens after the current passes through the loops of Niobium-Titanium Wires?

Answer 7

• the wires are super cooled
• this is done with Cryogens
• this eliminates any resistance within them

Question 8

8. What are Cyrogens?

Answer 8

• they are liquid Helium and Nitrogen

Question 9

9. What are the 4 advantages of Superconducting Electromagnets?

Answer 9

1. THEY GIVE HIGH MAGNETIC FIELD STRENGTHS
   - while requiring low power to do such
2. THEY HAVE LOW OPERATING COSTS
3. THEY CAN ACCOMMODATE ADVANCED
   APPLICATIONS
4. THEY HAVE OPTIMUM IMAGE QUALITY

Question 10

10. What are the 3 disadvantages of Superconducting Electromagnets?

Answer 10

1. THEY HAVE A HIGH CAPITAL COST
2. THEY NEED SHIELDING FROM RADIO FREQUENCY
3. THEY HAVE A TUNNEL DESIGN
   • this is unsuitable for large or claustrophobic patients

Question 11

11. What cannot be created with regards to Superconducting electromagnets?

Answer 11

• it is impossible to create an electromagnet with coils
  that are evenly spaced

THIS IS DUE TO:
- design limitations

Question 12

12. What is the issue that arises when we have unevenly spaced loops?

Answer 12

• this creates inhomogeneities in the Main Magnetic
  Field

Question 13

13. Define: Inhomogeneities.

Answer 13

• a part of the magnetic field that is not identical and
  continuous larger uniform mass in which it occurs

Question 14

14. How do we correct the unevenly spaced loops that create inhomogeneities?

Answer 14

• another loop of the wire is placed in the area of the
  inhomogeneity
• this loop of wire carries the current

Question 15

15. What is the advantage of adding another loop of the wire is placed in the area of the inhomogeneity?

Answer 15

• this compensates for the inhomogeneity in the main
  magnetic field
• this creates magnetic field homogeneity and evenness

NB:
- this process is known as SHIMMING
- the extra loop of wire is known as the SHIM COIL

Question 16

16. Does this image of the effect of the added Shim Coil make sense?

Answer 16

• yes

Question 17

17. What does this image show?

Answer 17

• this is an MRI
• it makes use of a Superconducting Electromagnet

NB:
- magnetic flux lines will indicate the direction of the
Magnetic Field lines