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Diffusion time dependency of extracellular diffusion
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DOI：10.1002/mrm.29594.png)
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Abstract
En 中文
Purpose: To quantify the variations of the power-law dependences on diffusion time t or gradient frequency f of extracellular water diffusion measured by diffusion MRI (dMRI).Methods: Model cellular systems containing only extracellular water were used to investigate the t/f dependence of D-ex, the extracellular diffusion coefficient. Computer simulations used a randomly packed tissue model with realistic intra-cellular volume fractions and cell sizes. DMRI measurements were performed on samples consisting of liposomes containing heavy water(D2O, deuterium oxide) dispersed in regular water (H2O). Dex was obtained over a broad t range (similar to 1-1000 ms) and then fit power-law equations D-ex(t) = D-const + const center dot t(-9)t and D-ex(f) = D-const + const center dot f( 9)f .Results: Both simulated and experimental results suggest that no single power-law adequately describes the behavior of D(ex )over the range of diffusion times of most interest in practical dMRI. Previous theoretical predictions are accurate over only limited t ranges; for example, theta(t )= theta(f) = - 1/2 is valid only for short times, whereas theta(t) = 1 or theta(f )= 3/2 is valid only for long times but cannot describe other ranges simultaneously. For the specific t range of 5-70 ms used in typical human dMRI measurements, theta(t )= theta(f) = 1 matches the data well empirically.Conclusion: The optimal power-law fit of extracellular diffusion varies with diffusion time. The dependency obtained at short or long t limits cannot be applied to typical dMRI measurements in human cancer or liver. It is essential to determine the appropriate diffusion time range when modeling extracellular diffusion in dMRI-based quantitative microstructural imaging.
Keywords:
D2O
diffusion
diffusion time
extracellular
liposome
oscillating gradient
phantom
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