Investigating the prevalence of complex fiber configurations in white matter tissue with diffusion magnetic resonance imaging

Abstract

It has long been recognized that the diffusion tensor model is inappropriate to characterize complex fiber architecture, causing tensor-derived measures such as the primary eigenvector and fractional anisotropy to be unreliable or misleading in these regions. There is however still debate about the impact of this problem in practice. A recent study using a Bayesian automatic relevance detection (ARD) multicompartment model suggested that a third of white matter (WM) voxels contain crossing fibers, a value that, whilst already significant, is likely to be an underestimate. The aim of this study is to provide more robust estimates of the proportion of affected voxels, the number of fiber orientations within each WM voxel, and the impact on tensor-derived analyses, using large, high-quality diffusionweighted data sets, with reconstruction parameters optimized specifically for this task. Two reconstruction algorithms were used: constrained spherical deconvolution (CSD), and the ARD method used in the previous study. We estimate the proportion of WM voxels containing crossing fibers to be $90% (using CSD) and 63% (using ARD). Both these values are much higher than previously reported, strongly suggesting that the diffusion tensor model is inadequate in the vast majority of WM regions. This has serious implications for downstream processing applications that depend on this model, particularly tractography, and the interpretation of anisotropy and radial/axial diffusivity measures. Hum Brain Mapp 34:2747-2766,

Changes in White Matter Organization in Adolescent Offspring of Schizophrenia Patients

“…The fact that we found an increased FA already at the onset of adolescence points to an altered development before the onset of adolescence (Paus et al, 2008;Rapoport et al, 2012) and may speculatively reflect an advanced peak of myelination (Beaulieu, 2002) or altered development of crossing fibers (Jeurissen et al, 2013) during childhood. This is in line with the idea that genetic factors, in combination with environmental factors, are likely to be at the base of this deficit.…”

Development of white matter and reading skills

“…For example, an increase in the density of axons in a fiber bundle that crosses through the arcuate or ILF would account for the decreases in FA that we measured in these fascicles for the poor readers. High-angular-resolution diffusion imaging can measure the effects of crossing fibers by quantifying the relative weights on multiple fiber populations within a voxel (49,50). An alternative explanation of the data, based on two processes that reflect neighboring pathway development, remains a real possibility.…”

Long‐term white matter tract reorganization following prolonged febrile seizures

“…The assumption that AD (i.e., axial/longitudinal/parallel diffusivity) is determined primarily by the intrinsic characteristics of axons and axonal integrity, and RD (i.e., radial/transverse/perpendicular diffusivity) by myelination, is overly simplistic, given that the relative contribution of WM tissue components to the diffusivity measures are yet to be accurately determined 34, 35. The interpretation of DTI metrics is even more ambiguous in regions of crossing fibers, where their values are likely to be confounded by changes in the relative fractions of the multiply oriented fiber populations 36, 37, 38. Although we cannot exclude the possibility that the observed DTI changes in the PFS group in our study could represent preexisting WM structural alterations in children predisposed to having PFS, the distribution, pattern, and the evolution of DTI changes in the context of previously reported short‐term changes suggest compensatory WM microstructural reorganization with increased axonal coherence as a more plausible explanation.…”