Atomic nuclei of interest in MRI studies have their own resonant frequencies, in the radiofrequency portion of the electromagnetic spectrum.
The receiver coil picks up the oscillations at RF frequencies produced by precession of the magnetic moment of nuclei inside the subject.
MRI scanners are generally situated in metal mesh lined rooms which act as Faraday cages.)
The condition to attain a high RF magnetic field homogeneity is to approximate spatial cosine current distribution in radiofrequency coil.
[5] The RF homogeneity of volume coils is highly desirable for transmission, but is less ideal when the region of interest is small.