Imaging Local Diffusive Dynamics Using Diffusion Exchange Spectroscopy MRI

Abstract

The movement of water between microenvironments presents a central challenge in the physics of soft matter and porous media. Diffusion exchange spectroscopy (DEXSY) is a powerful 2D nuclear magnetic resonance method for measuring such exchange, yet it is rarely used because of its long scan time requirements. Moreover, it has never been combined with magnetic resonance imaging (MRI). Using probability theory, we vastly reduce the required data, making DEXSY MRI feasible for the first time. Experiments are performed on a composite nerve tissue phantom with restricted and free water-exchanging compartments.

Magnetic resonance microdynamic imaging reveals distinct tissue microenvironments

“…This issue may be addressed by direct measurement of the exchange rate spectrum, either via relaxation exchange spectroscopy (REXSY) (Lee et al, 1993) or via diffusion exchange spectroscopy (DEXSY) (Callaghan and Fur’o, 2004). Spatially resolved, accelerated, and efficient REXSY and DEXSY experiments were recently demonstrated by using the MADCO framework (Bai et al (2016) and Benjamini et al (2017), respectively), and could be integrated with MRMI, as a complementary measurement. Alternatively, filter-exchange imaging may be used to obtain a single global apparent exchange rate value (Nilsson et al, 2013), assuming two exchanging compartments.…”

Brain active transmembrane water cycling measured by MR is associated with neuronal activity

“…In addition to these technical challenges, there are serious, looming safety and environmental issues that challenge all further CA use in humans . Encouraging developments in MRI methods suggest it may be possible to use non‐invasive diffusion‐based exchange MRI to measure and map k io in the brain, as well as in other tissues . In addition, k io measurement in vivo should be much less noisy than our in vitro measurement for the reasons given above .…”

“…17 Encouraging developments in MRI methods suggest it may be possible to use non-invasive diffusion-based exchange MRI to measure and map k io in the brain, as well as in other tissues. 17,[55][56][57][58][59] In addition, k io measurement in vivo should be much less noisy than our in vitro measurement for the reasons given above. 20 In this study, the k io from glial cells was not emphasized because of the low population of glia in this OCC preparation.…”

Measuring diffusion exchange across the cell membrane with DEXSY (Diffusion Exchange Spectroscopy)

“…A significant advantage of DEXSY is that it provides a model‐free approach to measuring diffusion exchange, and, as suggested by our numerical simulations, the DEI is perhaps more directly related to membrane permeability than AXR from FEXSY. A limitation of this study is the low spatial resolution and further work using rapid imaging techniques, to investigate the influence of heterogeneous tumor pathology (such as necrosis, edema, cysts), and phenomena such as changes in cell size and/or viscosity on DEI measurements should be undertaken. The hardware requirements for DEXSY and FEXI are very similar so it should be possible to implement DEXSY in clinical scanners.…”