Either the phase due to an applied field or field inhomogeneity and generated during the time between two RF pulses, or the phase change of the RF pulse from one pulse to the next.

A saddle coil has a cylindrical body, with one or more turns of wire (older versions) or foil (newer versions) on each side. It generates a very homogenous field in the direction of its long axis. To achieve a higher B₁ homogeneity there are different developments like Folded Litz-foil Saddle Coils or Etched Litz-foil Saddle Coils.

See also the related poll result: '3rd party coils are better than the original manufacturer coils'

Region of the object from which NMR signal will preferentially be acquired because of strong magnetic field inhomogeneity elsewhere. Effect can be enhanced by use of a shaped RF field that is strongest in the sensitive region.

Quick Overview

Uneven intensity or brightness may occasionally be noted on high field MRI e.g. of the brain. There are various causes of localized inhomogeneous brightness across the MRI images such as improper tuning of the RF transceiver, unbalanced deposition of the RF energy due to incorrect geometry and localized attenuation due to positioning or anatomical variants.

Tuning of the RF transceiver, a homogeneity correction filter and better positioning of the scanned object and/or coil in the scanner.

Correction of inhomogeneity of the magnetic field produced by the main magnet of a MRI system due to imperfections in the magnet or to the presence of external ferromagnetic objects. May involve changing the configuration of the magnet or the using of shim coils (active shimming) or adding or removing steel from the magnets poles (passive shimming) to fine-tune the magnetic field.

See also the related poll result: 'Most outages of your scanning system are caused by failure of'