Abstract
PurposeDiffusion magnetic resonance imaging (MRI) microstructure imaging provides a unique noninvasive probe into tissue microstructure. The technique relies on biophysically motivated mathematical models, relating microscopic tissue features to the magnetic resonance (MR) signal. This work aims to determine which compartment models of diffusion MRI are best at describing measurements from in vivo human brain white matter.MethodsRecent work shows that three compartment models, designed to capture intra-axonal, extracellular, and isotropically restricted diffusion, best explain multi-b-value data sets from fixed rat corpus callosum. We extend this investigation to in vivo by using a live human subject on a clinical scanner. The analysis compares models of one, two, and three compartments and ranks their ability to explain the measured data. We enhance the original methodology to further evaluate the stability of the ranking.ResultsAs with fixed tissue, three compartment models explain the data best. However, a clearer hierarchical structure and simpler models emerge. We also find that splitting the scanning into shorter sessions has little effect on the ranking of models, and that the results are broadly reproducible across sessions.ConclusionThree compartments are required to explain diffusion MR measurements from in vivo corpus callosum, which informs the choice of model for microstructure imaging applications in the brain. Magn Reson Med 72:1785–1792, 2014. © 2013 The authors. Magnetic Resonance in Medicine Published by Wiley Periodicals, Inc. on behalf of International Society of Medicine in Resonance.
Highlights
Diffusion magnetic resonance imaging (MRI) measures water diffusion in biological tissue, which can be used to probe the microstructure
Stanisz et al [3] pioneered the representation of separate compartmental diffusive processes in nervous tissue with a three compartment model consisting of: ellipsoidally restricted intra-axonal water, anisotropically hindered extracellular water, and isotropically restricted glial cell water. This was followed by the Ball-Stick model [4], which is intended as the simplest model that separates intra- and extra-axonal water signals
Several distinct groups of models emerge: (i) three compartment models with anisotropic extracellular compartment (Zeppelin/Tensor) and Dot/Sphere third compartment, which produce the best fit; (ii) three compartment models with anisotropic extracellular compartment and Astrostick/Astrocylinder third compartment, which are consistently worse than Dot/Sphere equivalents, but better than all other models; and (iii) three compartment models with isotropic extracellular compartment and all two compartment models
Summary
Diffusion MRI measures water diffusion in biological tissue, which can be used to probe the microstructure. Stanisz et al [3] pioneered the representation of separate compartmental diffusive processes in nervous tissue with a three compartment model consisting of: ellipsoidally restricted intra-axonal water, anisotropically hindered extracellular water, and isotropically restricted glial cell water. This was followed by the Ball-Stick model [4], which is intended as the simplest model that separates intra- and extra-axonal water signals. The ActiveAx technique [8,9] uses single diameter cylindrical restriction for intra-axonal water (simplifying the corresponding compartment of CHARMED), anisotropically hindered extracellular water, and a “Dot” compartment (simplifying Stanisz’s isotropically restricted glial cell compartment). Later versions of ActiveAx [10] accommodate dispersed orientations of the cylinders
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