GRADIENT COIL OF MRI

The ultimate goal of MRI is Image generation .The combination of static magnetic field and Radio frequency coils allows detection of MR signal but MR signal alone cannot be used to create an image .The fundamental measurement of MRI is merely the amount of current through a coil which in itself has no spatial information .Gradient coils provide the final touch up required for imaging .The main purpose of gradient coil is to cause MR signal spatially dependent in a controlled fashion. Gradient coils are generally turned off when Image acquisition is not required

To make the recovery of spatial information as simple as possible, gradient coils are used to generate a magnetic field that increases in strength along one spatial direction .The spatial direction used are relative to the main magnetic field, with Z axis parallel to main magnetic field and X and Y going perpendicularly to the main field .As previously gradient coils are evaluated on two criteria:: linearity and the field strength. The simplest example for gradient coil is MAXWELL pair. X and Y gradients are also called as Transverse Gradient both are created in the same fashion as Z, this transverse gradient changes the intensity of main field, and generally Golay pair is used is used .Strength of gradient coil is a function of both current density and the physical size of the coil