in an open magnetic resonance system , pole pieces on opposite sides of an imaging region are supported by a ferrous flux return path . during normal operation , environmental disturbances that cause low frequency vertical vibrations in the floor cause corresponding fluctuations in the main field of the magnet . a spacing between the pole pieces expands and contracts with the vibration causing a strength of the main field to fluctuate . a force transducer under the magnet assembly measures the magnitude of the vibrations . a vibration analyzer analyzes the vibrations waveform and calculates compensation for the changes in the interpole spacing . the vibration analyzer controls one or more of a shim coil which produces a field equal and opposite to the main field fluctuations , a reconstruction processor to compensate for magnetic field resonance frequency fluctuations attributable to the main field fluctuations , and gradient magnetic fields applied by gradient field coils .