Spatial Gradient Maps

The spatial gradient magnetic field describes how the strength of a magnetic field changes over distance. Ferrous objects, when exposed to varying magnetic fields, are pulled towards stronger fields and continue moving until they encounter a field that is not changing or collide with another object. This variation in magnetic strength over distance is defined by the formula dB/dx and is measured in Tesla per meter (T/m) or Gauss per centimeter (G/cm). 1  T/m = 100G/cm. The “d” stands for a change in, the “B” stands for magnetic flux, and the “x” stands for distance. Each MRI manufacturer provides a system manual with spatial gradient field maps specific to the MR system. Often the maps are shown in different angles, such as profile, sagittal, top, or front views and are crucial because MR Conditional implants have maximum spatial field gradient limits that they can experience. At UCSF, MRI personnel use these maps as a reference, understanding these maps is key to ensuring implants meet MR conditional safety requirements. 

The following excerpts are drawn from the manufacturer’s system manuals, detailing the spatial gradient field maps for the majority of MR systems employed at UCSF.