Gradient coils

The gradient coils are three sets of wire coils wrapped around a fiberglass cylinder located within the magnet housing. Electric current flows through the coils and is turned on and off very rapidly, thereby producing expansion and contraction of the gradient coils. This expansion and contraction creates the tapping sound when scanning. It is commonly measured in gauss per centimeter.

Each coil affects a different plane (the XY, YZ, or XZ plane), as it is turned on and off at different points in a pulse sequence. The scan plane and pulse sequence selected determine which gradient functions as the slice selective, phase encoding, and frequency encoding gradient. The system calculates this automatically.

The gradients are resistive magnets and are water cooled by the gradient chiller located in the Equipment cabinet room.