MRI Gradient Coils: Types and Function

Gradient Coils: Types and Function

• Gradient coils create a variable magnetic field within an MRI machine
• There are three sets of gradient coils, one for each direction (x, y, and z)
• The variation in the magnetic field allows for the localization and imaging planes
• Z-axis coils are Helmholtz pairs
• X and Y-axis coils are paired saddle coils

Gradient Coil Production

• Magnetic field strength is proportional to current, number of loops, loop size, and spacing.

• Gradient strength (stiffness) is measured in G/cm or mT/m

• Stronger gradients like 15 or 20 mT/m enable high speed and high-resolution imaging

• Gradient coils are a set of wires in the magnet, creating additional fields built upon the main magnetic field (B0)

• Three sets of wires create Z, X, or Y-directional magnetic fields

• When a current is passed through the coil, a magnetic field is generated within a specific direction.

• Gradient coils provide a linear magnetic field variation from one end of the solenoid to the other

• These are applied by passing current through the coil in a particular direction

• This either increases or decreases the magnetic field around the isocenter (center)

• The generated field is very strong, causing the coils to vibrate leading to noise

•  The 3 gradient coils form a cylindrical shape, fitted into the MRI magnet bore

• MRI systems use three sets of gradient coils to produce the x, y, and z planes