Radiofrequency receiver

Radiofrequency coils are the radiofrequency receivers (as well as sometimes the transmitters) of the electromagnetic signal used in MRI. Radiofrequency coils can be either receive-only, or both receivers and transmitters of the radiofrequency signal. The receiver coils detect the electromagnetic radiation produced by the process of nuclear relaxation inside the subject as a result of the transmitted electromagnetic field. The receiver coil is capturing the oscillating net magnetic flux from the excited spin system when an induced electric current is generated. This information is amplified, quantified and filtered to extract frequency and phase. The type of receiver coil used can be specified for the specific type of imaging required. Two of the factors which will determine the ability of a coil to receive signal are the proximity to the signal and the diameter of the coil (the larger the diameter, the less sensitive the coil).

One of the most common types of receive-only coils is the surface coil. Receive-only coils can also be used in parallel imaging applications, where they are aligned in large arrays. These are calls phased array coils.