Spectral fitting: the extraction of crucial information from a spectrum and a spectral image.

A highly accurate line-width simulation computer program is used that can account for both high amplitude and frequency of the Zeeman modulation in an electron paramagnetic resonance (EPR) experiment. This allows for the overmodulation of EPR lines to increase signal-to-noise ratio (SNR) in EPR spectra and spectroscopic images, without any sacrifice in the determination of the intrinsic line width (1/gamma. T(2e)). The technique was applied to continuous-wave EPR spectroscopic images of a narrow, single-line trityl spin probe wherein a full EPR spectrum was extracted from each 3D spatial voxel. Typical improvements are a three- to fivefold increase in SNR in the high-gradient projections in the image and a reduction in the standard deviation (SD), by a factor of 3, of the line widths in the low-gradient domain. This method is a general one that is also applicable to the analysis of conventional (14)N or (15)N nitroxide spin probes.