Imaging Magnets

Imaging magnets

main component of MRI system.

Magnet types

include permanent, resistive, and superconducting.

Permanent Magnet

Simplest in design and least expensive to operate.

Permanent magnet limitation

low field strength around 0.3 T.

Resistive magnet

requires continuous power and water cooling.

Resistive magnet field strength

approximately 0.15 T.

Resistive magnet

Uses 4 large coils

Resistive Magnet Advantages

Low capital cost, easy coil maintenance, negligible fringe field.

Resistive Magnet Disadvantages

High power consumption, water cooling required, significant fringe field.

Superconducting magnet

uses zero-resistance coils for high field strength.

Superconducting magnet cooling

uses liquid helium and nitrogen.

Superconducting Magnet

Contains coils made from a superconducting metal alloy with no electrical resistance.

Dewar

a double-walled flask of metal with vacuum between the walls.

Cryogens

Cooling Agents

Liquid nitrogen

(97 K) in outermost chamber

Liquid helium

(47 K) in innermost chamber.

Superconducting Magnet Advantages

High field strength (2 T), high field homogeneity, lower power consumption.

Superconducting Magnet Disadvantages

High capital cost, high cryogen cost, intense fringe field