Slew rate

Slew rate refers to the speed at which a gradient can be turned on and off, and is defined as the maximum gradient strength of the gradient divided by the rise time.

MR imaging is a product of magnetic field gradients which are created by magnetic gradient coils. The quality and performance of a gradient coil will directly impact the quality and resolution of the final image. One of the more important characteristics or specifications of a gradient coil is its slew rate (along with strength of the gradient). The slew rate will help define the maximum scan speed of the system.

Maximum gradient strength is measured in units of millitesla per meter (mT/m), rise time is measured in milliseconds, and slew rate is measured in tesla per meter per second (T/m/s). Typical figures for slew rates range between 50 T/m/s for lower field permanent scanners, up to around 200 T/m/s for high field superconducting scanners.

In practical terms, the slew rate will help determine the minimum attainable TR and TE in MR imaging, as well as the echo spacing in echo applications. Slew rate is dependent on both the gradient coil itself, as well as the gradient amplifier (which acts to overcome the inductance of the coil).

High slew rate can cause peripheral nerve stimulation .