Figure 1
Experimental design considerations for time-dependent diffusion. (A) Time-dependent diffusion can be considered in either time or frequency domains. For general diffusion encoding gradient waveforms, the diffusion times are ill defined. Thus, the frequency domain formulation provides a more stringent description of the signal. (B) The signal attenuation factor β from an individual compartment is given by the diffusion spectrum filtered by the encoding power spectrum. (C) The gradient waveforms (left panels) and the corresponding encoding power spectra (right panels) used in this study. The isotropic encoding has similar encoding power spectra in three orthogonal directions (different shades of gray) (top). The two directional encodings have the same total encoding power, i.e. b-value, but with either similar (tuned) or different (detuned) power spectra compared to the isotropic encoding. Note the increased encoding power at lower frequencies in case of detuned encoding. Time and frequency scales are shown for our experimental settings with the encoding time τ = 23 ms.
