In mathematics, the Gibbs phenomenon (also known as ringing artifacts, named after the American physicist J. Willard Gibbs) is the peculiar manner in which the Fourier series of a piecewise continuously differentiable periodic function f behaves at a jump discontinuity: the nth partial sum of the Fourier series has large oscillations near the jump, which might increase the maximum of the partial sum above that of the function itself. The overshoot does not die out as the frequency increases, but approaches a finite limit.
In MRI, artifactual ripples parallel to abrupt and intense changes are caused by the Fourier transformation.

See Gibbs Artifact, Truncation Artifact, Ringing Artifact Reduction.

See Gibbs Artifact.

Short name: GN-1140, chemical compound: Gd-DTPA-DeA, central moiety: Gd, phase: II
Gd-DTPA-DeA [Welfide Corp., Osaka, Japan], a paramagnetic MR contrast agent with hepatobiliary excretion is under development for liver imaging. This hydrophilic gadolinium chelate is a derivative of Gd-DTPA.

This term is commonly used for a particular kind of gradient coil, commonly used to create magnetic field gradients perpendicular to the main magnetic field. A golay coil (a special kind of saddle coils) produces a linear gradient in the x and y axes that requires wires running along the bore of the magnet. Such a coil produces a very linear field, but the linearity is lost rapidly away from the central plane. A number of pairs with different axial separations can be used to improve this.

The word gradient (from grade) means the inclination of a surface along a given direction. In MRI, gradient stands for gradient field and/or gradient coil. Inside the main magnet are three gradient coils located, which produce the desired gradient (magnetic) fields. These fields are used to alter (collectively and sequentially) the influence of the static magnetic field B0 on the imaged object by inc- or decreasing the field strength and changing the direction. Through this influence selective spatial excitation and spatial encoding (each voxel resonate at a different frequency) is possible. Gradients are also utilized in another way for fast imaging sequences.

See also Slew Rate and Duty Cycle.