Diffusion effects on longitudinal relaxation in poorly mixed compartments

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.

Uncertainty estimations for quantitative in vivo MRI T1 mapping

“…This is strictly speaking incorrect, as studies have shown that even without obvious partial volume effects the longitudinal relaxation displays multi-exponential behavior [12]. However, to be able to reliably estimate the shorter of the T 1 components, the inversion curve should be sampled at sufficiently short inversion times and at close intervals.…”

Semipermeable hollow fiber phantoms for development and validation of perfusion‐sensitive mr methods and signal models

“…As a consequence, we routinely use a new phantom for each set of experiments. Nonetheless, this effect did not impact any of our individual experiments, the longest of which lasted 15 h (23). …”

“…Because of differences in proton density, the fiber walls appear hypointense in these images. R 1 -mapping has established that, in the absence of lumenal flow, there is no significant difference in longitudinal rate constant in the fiber wall compared to homogeneous solution (23). Figure 5 shows representative spin-echo transaxial images from the same phantoms as in Fig.…”

“…The fibers in this figure appear hyperintense; the region of hyperintensity extends into the extrafiber space. This interesting effect is due to diffusion-driven longitudinal relaxation (vide infra) (23). …”

Nuclear spin relaxation in liquids and gases

“…Anderson et al 68 discussed diffusion of spins between compartments, characterized by different states of longitudinal magnetization, leading to diffusion-driven longitudinal relaxation. The effects were explored experimentally and analyzed quantitatively.…”