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Updated: Jun 2, 2026

The Diffusion of Passive Tracers in Laminar Shear Flow
Published on: May 1, 2018
Diffusion effects on longitudinal relaxation in poorly mixed compartments
1Department of Chemistry, Washington University, St. Louis, MO 63130, USA.
Abstract:
Diffusion of spins between physical or virtual, communicating compartments having different states of longitudinal magnetization leads to diffusion-driven longitudinal relaxation. Herein, in two model systems, the effects of diffusion-driven longitudinal relaxation are explored experimentally and analyzed quantitatively. In the first case, longitudinal relaxation in a single slice of a water phantom is monitored spectroscopically as a function of slice thickness. In the second case, mimicking vascular flow/diffusion effects, longitudinal relaxation is monitored in a two-compartment, semi-permeable fiber phantom. In both cases, apparent longitudinal relaxation, though clearly multi-exponential, is well-modeled as bi-exponential.
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