Mapping water exchange in the human brain using diffusion MRI with free waveform encoding
Arthur Chakwizira1, Filip Szczepankiewicz2, Carl-Fredrik Westin3, Geraline Vis4, Linda Knutsson1,5,6, Pia Sundgren7,8,9,10, and Markus Nilsson2
1Medical Radiation Physics, Lund, Lund University, Lund, Sweden, 2Clinical Sciences Lund, Lund University, Lund, Sweden, 3Department of Radiology, Brigham and Women's hospital, Harvard Medical School, Boston, MA, United States, 4Department of Diagnostic Radiology, Clinical Sciences Lund, Lund University, Lund, Sweden, 5Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, United States, 6F. M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, United States, 7Department of Diagnostic Radiology, Lund University, Lund, Sweden, 8Lund University Bioimaging Center, Lund University, Lund, Sweden, 9Department for Medical Imaging and Physiology, Skåne University Hospital, Lund, Sweden, 10Department of Radiology, University of Michigan, Ann Arbor, MI, United States
Temporal velocity correlations of diffusing particles carry information about the structure of the diffusion environment. Studying high-order velocity autocorrelation functions can aid in understanding how signal is influenced by restricted diffusion and exchange, and in turn how to design experiments that are sensitive/independent to these phenomena. In this work, we employ numerical simulations on a variety of substrates to demonstrate this notion. We find that the fourth order velocity autocorrelation bears a distinctive signature of exchanging systems. In addition, we highlight that the effect of exchange on the second order velocity autocorrelation is negligible when exchange is barrier-limited.
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