A coil consists of one or more loops of conductive wire, looped around the core of the coil. Coils are part of the hardware of MRI machines and are used to create a magnetic field or to detect a changing magnetic field by voltage induced in the wire. A coil is usually a physically small antenna.
The perfect coil produces a uniform magnetic field without significant radiation.
Different types of MRI coils are used in MR systems:
Gradient coils are used to produce controlled variations in the main magnetic field (B0) to provide spatial localization of the signals and to apply reversal pulses in some imaging techniques.
MR imaging radio frequency coils to receive and/or transmit the RF signal.
Shim coils provide auxiliary magnetic fields in order to compensate for inhomogeneities in the main magnetic field of the MRI machine.

See also Gradient Coil, Radio Frequency Coil, Hardware and Coil Loading.

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

The body coil is installed in the magnet and functions both as transmit than also as a receiver coil. This coil has a large measurement field, but does not have the high SNR of special coils. When specific receiver only coils are used (the most surface coils), the body coil serves as the transmit coil.

An array coil combines the advantages of smaller coils (high SNR) with those of larger coils (large measurement field). This type of RF coil is composed of separate multiple smaller coils, which can be used individually (switchable coil) or combined.
When used simultaneously, the elements can either be:
See also the related poll result: '3rd party coils are better than the original manufacturer coils'

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.

An RF array coil consisting of 2 - 6 several separately resonant elements, 2 or more of which can be selected as the receiver coil at a particular time. Coils not in use are decoupled. The spatial information related to the coils of a receiver array are utilized, reference images are required, obtained with each array element and with a body coil. Fast parallel imaging techniques using surface multicoils, such as sensitivity encoding (SENSE) or simultaneous acquisition of spatial harmonics (SMASH), have recently raised interest in the field of MR imaging.

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