The operation of superconducting magnets at temperatures below 4.2 K

A Quantum Mechanical Review of Magnetic Resonance Imaging

“…Current day machines typically use superconducting electromagnets. These are wire coils cooled to low temperatures using liquid helium and liquid nitrogen [29,63,14,47,44,107,71,111], allowing for greatly decreased electrical resistance, and consequently high current loops generating strong magnetic fields. The RF coil typically serves both as the generator of the pulsed magnetic field, and as the detector of the FID signal.…”

“…Y l,m are called the spherical harmonic functions and are discussed some more in the following subsection. Figures (14) to (23) are plots of a sampling of spherical harmonics with 1 ≤ l ≤ 5.…”