Impact of transcytolemmal water exchange on estimates of tissue microstructural properties derived from diffusion MRI

To investigate the influence of transcytolemmal water exchange on estimates of tissue microstructural parameters derived from diffusion MRI using conventional PGSE and IMPULSED methods.

Computer simulations were performed to incorporate a broad range of intracellular water life times τ_in (50-∞ ms), cell diameters d (5-15 μm), and intrinsic diffusion coefficient D_in (0.6-2 μm² /ms) for different values of signal-to-noise ratio (SNR) (10 to 50). For experiments, murine erythroleukemia (MEL) cancer cells were cultured and treated with saponin to selectively change cell membrane permeability. All fitted microstructural parameters from simulations and experiments in vitro were compared with ground-truth values.

Simulations showed that, for both PGSE and IMPULSED methods, cell diameter d can be reliably fit with sufficient SNR (≥ 50), whereas intracellular volume fraction f_in is intrinsically underestimated due to transcytolemmal water exchange. D_in can be reliably fit only with sufficient SNR and using the IMPULSED method with short diffusion times. These results were confirmed with those obtained in the cell culture experiments in vitro.

For the sequences and models considered in this study, transcytolemmal water exchange has minor effects on the fittings of d and D_in with physiologically relevant membrane permeabilities if the SNR is sufficient (> 50), but f_in is intrinsically underestimated. Magn Reson Med 77:2239-2249, 2017. © 2016 International Society for Magnetic Resonance in Medicine.