The principle of reciprocity in signal strength calculations—A mathematical guide

Confusion exists over the application of the Principle of Reciprocity to NMR signal strength calculations when wavelength in a sample is comparable to the latter's size. A simple and easily reproduced bench experiment that validates the principle is therefore described. Building on the experimental results, elementary mathematics are employed to derive simple equations for the B1 fields in both the negatively and the positively rotating frames. Using these equations, the reader is then guided through the steps needed to deduce correctly the signal received in an NMR experiment. The article should serve as a resource for those attempting signal strength calculations. © 2000 John Wiley & Sons, Inc. Concepts Magn Reson 12: 173–187, 2000