Dynamic<i>q</i>space microscopy of cellular tissue

TLDR

The authors use a multiple‑exponential time‑series expansion of the NMR pulsed‑gradient spin‑echo signal S(q,Δ,τ) to derive the static structure factor from the lowest‑order term at long Δ and obtain dynamic information from higher‑order coefficients, thereby enabling analysis of multicompartment cellular tissue. They find that spatially inhomogeneous relaxation distorts the apparent static and dynamic structure factors, that changes in compartment morphology alter the coupling of relaxation and diffusion, and that fitting apple parenchyma data yields a plasmalemma permeability of 1.2 × 10⁻³ cm s⁻¹.

Abstract

A multiple exponential time series expansion is used to analyse the dependence of the NMR pulsed gradient spin-echo amplitude S(q, Δ, τ) on the wavevector q, the pulsed gradient separation Δ and the 90–180° pulse separation τ in multicompartment systems such as cellular tissue. The static structure factor measured in q space microscopy is obtained as the lowest order coefficient in the time expansion at long Δ. Dynamic information is obtained from the wavevector dependence of the higher order coefficients. Spatially inhomogeneous relaxation is shown to distort the apparent static and dynamic structure factors. Changes in compartment morphology alter the coupling of relaxation and diffusion reflected in the wavevector dependent relaxation times obtained when Δ and τ are varied together. By fitting the data for parenchyma tissue of apple with a numerical cell model, a plasmalemma membrane permeability of 1·2 × 10-3 cm s-1 is derived.