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Processing of ND NMR spectra sampled in polar coordinates: a simple Fourier transform instead of a reconstruction
Authors:Dominique Marion
Institution:(1) Institut de Biologie Structurale “Jean-Pierre Ebel”, CNRS-CEA-UJF, 41, Rue Jules Horowitz, 38027 Grenoble Cedex 1, France
Abstract:In order to reduce the acquisition time of multidimensional NMR spectra of biological macromolecules, projected spectra (or in other words, spectra sampled in polar coordinates) can be used. Their standard processing involves a regular FFT of the projections followed by a reconstruction, i.e. a non-linear process. In this communication, we show that a 2D discrete Fourier transform can be implemented in polar coordinates to obtain directly a frequency domain spectrum. Aliasing due to local violations of the Nyquist sampling theorem gives rise to base line ridges but the peak line-shapes are not distorted as in most reconstruction methods. The sampling scheme is not linear and the data points in the time domain should thus be weighted accordingly in the polar FT; however, artifacts can be reduced by additional data weighting of the undersampled regions. This processing does not require any parameter tuning and is straightforward to use. The algorithm written for polar sampling can be adapted to any sampling scheme and will permit to investigate better compromises in terms of experimental time and lack of artifacts.
Keywords:digital resolution  Fourier transformation  non-linear sampling  polar coordinates
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