Two-Dimensional Fourier Transformation in NMR

The idea of two-dimensional Fourier transformation was originated by Jeener (1) in 1971, but the very wide significance of his proposal does not seem to have been generally realized until several years later, when several elegant applications were described (2-6). The basic idea is very simple. In modern nmr spectrometers, spectra are normally obtained by Fourier transformation of a transient free precession signal, which we shall call S(t2), where t2 is the usual running time variable for signal acquisition. However, the phase and amplitude of S(t2) are dependent on the history of the nuclear magnetization prior to t2 = 0. We may define the interval immediately preceeding t2 as an evolution period f, during which the spectrometer receiver is inactive but the nuclear spins are forced to execute some prescribed motion that will influence the detected signal S(r2) in some manner. Jeener's idea was to increment f, over a suitable range of values and perform a second Fourier transformation of the signal as a function of tu thus mapping out the behavior of the nuclear magnetization during the evolution period as well as during the detection period f2.