Effect of diffusion-sensitizing gradient timings on the exponential, biexponential and diffusional kurtosis model parameters: In-vivo measurements in the rat thalamus

Object: To investigate whether spacing (Δ) and duration (δ) of the diffusion-sensitizing gradient pulses differentially affect exponential (D′), biexponential (D _slow, D _fast and f _slow) and diffusional kurtosis (D and K) model parameters. Methods: Measurements were performed in the rat thalamus for b = 200-3,200 s mm ^-2, sweeping Δ between 20 and 100 ms at δ = 15 ms, and δ between 15 and 50 ms at Δ = 60 ms. Linear regressions were performed for each model parameter vs. Δ or δ. Results: Increasing Δ from 20 to 100 ms increases D′ (from 0.64 to 0.70 × 10 ^-3 mm²s^-1) and D _slow (from 0.26 to 0.33 × 10^-3 mm²s^-1), reduces K (from 0.57 to 0.53), and has no effects on D _fast, f _slow or D. Increasing δ from 15 to 50 ms increases D (from 0.80 to 0.88 × 10^-3 mm²s^-1), and has no effects on the other parameters. Conclusion: The parameters of the biexponential and diffusional kurtosis models are more sensitive than the exponential model to Δ and δ; however, observed effects are too small to account for the discrepancies found in literature.