Echo planar magnetic resonance imaging of anisotropic diffusion in asparagus stems

MR diffusion-weighted imaging (DWI) uses the signal loss associated with th e random thermal motion of water molecules in the presence of magnetic fiel d gradients to derive a number of parameters that reflect the translational mobility of the water molecules in tissues. In highly organized but asymme tric structures, this mobility may be affected by the obstacles present and this in a direction-dependent way. Important examples of this are white br ain matter and the stem of certain plants, both containing fibrous componen ts where diffusion of water molecules across fibers is much more restricted than along the fibers. Diffusion that exhibits such directional dependence is said to be anisotropic, and diffusion tensor magnetic resonance imaging allows localized characterization of this behavior. Interpretation of the information obtained in terms of the underlying tissue structure is often h ampered by the complexity of factors that can produce the observed behavior . A phantom that exhibits well-defined anisotropic diffusion and yields suf ficient signal can help the experimental testing of the relevant methods an d models. In this paper, we have used a phantom consisting of asparagus ste ms as a test object for assessing the value of the acquisition and postproc essing techniques commonly used in the clinic for this kind of investigatio n. Because of its strongly fibrous and cylindrically symmetric morphology, exhibiting a well-defined sub-classification of cells on the basis of size and shape, asparagus allows a relatively simple interpretation of the resul ts obtained in the diffusion experiments. Our experiments show that the kno wn structural information about the main cell types encountered correlates well with the behavior patterns of the diffusion parameters. (C) 2001 Elsev ier Science B.V. All rights reserved.