Pair of current carrying coils used to create uniform magnetic field in the center of the space between them. For circular coils, their separation equals their radius.

A coil that produces an RF field with circular polarization. The RF power received from the RF power amplifier comes in two signals (quadrature detection), which have a phase difference of 90°. The RF transmit coil converts the power into a circularly polarized RF magnetic field.
Quadrature coils can be used as both, transmit and/or receive coil. When used as a transmitter coil a factor of two power reduction over a linear coil results; as a receiver an increase in SNR of up to a factor of √2, can be achieved.

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

An RF array coil consisting of several separately resonant elements, any one of which can be selected as the receiver coil at a particular time. Coils not in use are decoupled. Applications of switchable coils include imaging the whole spine without patient repositioning (where the coil elements may collectively be known as a ladder coil), imaging of bilateral structures such as TMJ or orbit using separate coils, or imaging using a coil with selectable field of view.

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

A surface coil placed over a region of interest will have an effective selectivity for a volume approximately subtended by the coil circumference and one radius deep from the coil center. Such a coil can be used for simple localization of sites for measurement of chemical shift spectra, especially of phosphorus, and blood flow studies. Some additional spatial selectivity can be achieved with magnetic field gradients.

The coil of the RF transmitter, inside the MR imager is used in excitation of the spins. Also called transmit-only coil it is used to create the B1 field. As a radio frequency generator send this coil bursts of RF pulses. These pulses serve to disturb the spins in the patient.