magnetism

Question 1

What types of magnets are used in Magnetic Resonance Imaging (MRI)?

Answer 1

In MRI, permanent magnets and electromagnets are used. Electromagnets are further divided into resistive and superconducting magnets.

Question 2

What are permanent magnets composed of, and what is their typical magnetic field strength?

Answer 2

Permanent magnets are composed of permanently magnetized ceramic bricks assembled to generate a strong magnetic field. They are typically very heavy and limited to magnetic fields no higher than 0.3T.

Question 3

What is the main characteristic of superconducting magnets that allows them to conduct electricity with no resistance?

Answer 3

• use a coil of wire to carry the electrical current and generate the magnetic
  field.
• The type of wire used is made of a blend of special elements which when kept
  extremely cold have no resistance to the flow of electricity through them.
• This property of a wire to conduct electricity with no resistance is called
  superconductivity.
• The absence of resistance allows a very high current to flow through the wire
  without generating a lot of heat.
• The wire is kept sufficiently cold and this results in constant supply of electrical
  current and resultant magnetic field.
• The wire is therefore immersed in a cryogen (an extremely cold liquid) such as
  helium temperature of -269oC. They produce magnetic fields of up to 1.5T – 3T
  for routine clinical imaging. The liquid helium needs replacement once in a
  while

Question 4

How is the wire in superconducting magnets kept cold, and what is the typical temperature?

Answer 4

The wire is kept cold by immersing it in a cryogen, such as liquid helium, at a temperature of -269°C.

Question 5

What is the range of magnetic field strengths produced by superconducting magnets for routine clinical imaging?

Answer 5

Superconducting magnets produce magnetic fields of 1.5T to 3T for routine clinical imaging.

Question 6

Why do permanent magnets cost very little to operate once they are in place?

Answer 6

Permanent magnets cost very little to operate once in place because they do not require power to maintain their magnetic field

Question 7

What needs to be periodically replaced in superconducting magnets, and why?

Answer 7

The liquid helium used to keep the wire cold needs to be periodically replaced to maintain the superconducting state.