Virtual photons in magnetic resonance

AbstractMagnetic resonance often relies on a semi‐classical picture in which the spin particles are submitted to quantum theory and the electromagnetic field is treated as a classical field. Although in many applications there are very good reasons to work within this theoretical framework, it appears worthwhile either for educational purposes, or for studies in magnetic resonance with microscopically small samples or very weak rf fields as well as for other applications that may seem exotic today, to ask how to gain a unified view when comparing the concepts and methods of quantum electrodynamics (QED) with those of classical electrodynamics commonly used in magnetic resonance. The present article attempts to develop such a unified view for electromagnetic interactions in magnetic resonance by focusing on the concept of virtual photon exchange based on the Feynman propagator technique and by exploring the cross links between basic aspects of “semi‐classical magnetic resonance” and the same basic aspects of magnetic resonance as seen through the frame of QED. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part A 36A: 266–339, 2010.