An MRI coil is an emission and/or reception device used during magnetic resonance imaging.
Applications
These devices are integrated into MRI equipment to optimize visualization of certain parts of the body.
Technologies
Surface coils are flat and placed in contact with the area to be examined. They are receivers only. In contrast, volume coils can be both emitters and receivers, or simple receivers. These are used for whole-body imaging or, in smaller versions, for more precise targeting.

Some coils are used alone, as linear antennas. Others are combined in a quadrature phase relationship or in a phased array to improve the signal-to-noise ratio by using several small coils.
How to choose
Choice will depend on the part of the body to be imaged, taking into account the size of the coil and its flexibility.