Figure 1.

(a) An example of two orthogonal gradient components of an elliptically oscillating gradient vector with ellipticity angle χ = 30° and modulation frequency ω_m. The waveforms shown are the effective gradients with inverted polarity after the 180°-pulse in this spin echo experiment. (b) The dephasing vector components calculated as the time integral of the gradients in a). (c) The weighting filter of the diffusion spectrum tensor is given by the elements of F(ω)F^Τ(−ω). The diagonal elements are real with the same distinct peak at the modulation frequency in both axes but with modulated strengths (solid lines). The off diagonal elements are complex (real (dashed), imaginary (dotted)) but integrate to zero. (d) Examples of temporal diffusion spectra of large and small restrictions. The gradient trajectory in (a) would mainly filter out the diffusivity around ω_m.