PSEUDOMODULATION - A COMPUTER-BASED STRATEGY FOR RESOLUTION ENHANCEMENT

Pseudomodulation is defined as computer simulation of the effect on a magnetic resonance spectrum that would be obtained if a sinusoidal field modulation were applied followed by phase-sensitive detection at the fundamental frequency or at one of its harmonics. Since it is done by computer, it is not necessary that it actually be possible to modulate the field. The algorithm is developed here for EPR spectroscopy, but can be applied to any function or to any digitized signal, including an NMR signal, and there can be more than one independent parameter, as, for example, an MR image or a 2D NMR spectrum where there are two. Pseudomodulation transforms and filters a digitized spectrum. Subtraction or addition of various amounts of the even harmonics of the digitized spectral data from or to the original spectrum results in resolution enhancement. Other resolution-enhancement algorithms that use pseudomodulation are also presented. Resolution enhancement by pseudomodulation is tested on simulated spectra to which computer-generated noise has been added and is applied to the EPR S-band spectrum of the blue copper protein azurin. © 1992.