Abstract
Diffusion-weighted magnetic resonance imaging (DW-MRI) is a non-invasive technique to probe tissue microstructure. Conventional Stejskal–Tanner diffusion encoding (i.e., encoding along a single axis), is unable to disentangle different microstructural features within a voxel; If a voxel contains microcompartments that vary in more than one attribute (e.g., size, shape, orientation), it can be difficult to quantify one of those attributes in isolation using Stejskal–Tanner diffusion encoding. Multidimensional diffusion encoding, in which the water diffusion is encoded along multiple directions in q-space (characterized by the so-called “b-tensor”) has been proposed previously to solve this problem. The shape of the b-tensor can be used as an additional encoding dimension and provides sensitivity to microscopic anisotropy. This has been applied in multiple organs, including brain, heart, breast, kidney and prostate. In this work, we discuss the advantages of using b-tensor encoding in different organs.
Highlights
1.1 BackgroundDiffusion magnetic resonance imaging sensitizes the signal to the random motion of the water molecules in the tissue [1]
An increase in the variance of mean diffusivity (VMD, the variance in mean diffusivities between local microenvironments) was observed. This cannot be explained by a homogeneous increase in the local mean diffusivity but it shows a higher fraction of free water
Previous studies in breast lesions showed that the tissue cellularity is inversely correlated with MD. [33] showed that isotropic diffusivity in fibroglandular breast tissue (FGT) (Ħ 2 × 10−3mm2/s) [139,140,141] were significantly higher than cancers which is in agreement with previous findings on MD [142,143,144,145].[33] reported that the fractional anisotropy and microscopic anisotropy values in FGT were significantly lower than tumors, in line with the previous literature [139,146].In healthy breast tissue, there are elongated structures such as lobules, ducts, and stroma in FGT that have large diameters compared to the mean displacement of water molecules during the diffusion time [139]
Summary
Diffusion magnetic resonance imaging (dMRI) sensitizes the signal to the random motion of the water molecules in the tissue [1]. Diffusion MRI has been used in diagnosis of other diseases, such as epilepsy, stroke, tumors in central nervous system, breast and prostate, as well as surgical planning [12,13,14,15,16,17,18,19,20,21,22]. Diffusion MRI has been invaluable in the study of brain development [23], learning [24,25], and connectivity [26,27]. Diffusion MRI has been used in the imaging of other. We briefly explain different diffusion encoding schemes and the advantages of using advanced diffusion encoding in brain and body imaging are discussed
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