Influence of radiofrequency amplifier nonlinearities on nuclear magnetic resonance image quality.

The quality of nuclear magnetic resonance (NMR) image is degraded by a number of disturbing influences. In this article the influence of a nonlinear radiofrequency receiving amplifier is investigated. The effect of a cubic nonlinearity on the NMR signal is analyzed. Finally, the influence on the NMR image is studied for Fourier reconstruction techniques. As a result, the images are degraded by an additional term which is proportional to a parameter characterizing the nonlinearity. The additional term causes homogeneous objects to appear inhomogeneous and gives rise to image intensity outside the object. Under normal conditions the image degradation is negligible.