Figure 4
A) Illustrative depiction of neurite density and orientation dispersion (arborization) of dendritic trees within the cerebral cortex. Brain cortical variations in such microstructural gray matter indices, which may be present in patients with psychiatric disorders, can now be assessed using neurite orientation dispersion and density imaging (NODDI).
167167. Zhang H, Schneider T, Wheeler-Kingshott CA, Alexander DC. NODDI: practical in vivo neurite orientation dispersion and density imaging of the human brain. Neuroimage. 2012;61:1000-16. NODDI requires multishell/high angular resolution diffusion imaging (HARDI) acquisitions using magnetic resonance imaging (MRI). Please note that the figure is only meant for illustration and does not represent the actual spatial resolution achieved by NODDI (adapted from Genç et al.,
169169. Genç E, Fraenz C, Schlüter C, Friedrich P, Hossiep R, Voelkle MC, et al. Diffusion markers of dendritic density and arborization in gray matter predict differences in intelligence. Nat Commun. 2018;9:1905. licensed under Creative Commons Attribution 4.0 International License). B) 3D schematic representation of a multishell encoding scheme generated using a gradient tool available at the Multiple Acquisitions for Standardization of Structural Imaging Validation and Evaluation (MASSIVE) website (
http://www.massive-data.org/). The gradients (colored dots) are magnetic field pulses that sensitize diffusion in a particular direction; by doing this, MRI scans can obtain information related to the dispersion of water molecules for each voxel. The colored dots show each randomly defined gradient direction. For each shell, there is an operator-selected parameter called the b-factor that defines gradient strength and duration. In this example, each gray circumference represents one of the shells: the inner one has a b-value of 1,000 s/mm
2 (gradients represented in pink); the outermost one has a b-value of 3,000 s/mm
2 (dark blue gradients); and, in between, a shell with a b-value of 2,000 s/mm
2 (green gradients). The grey dots represent the diametrically opposite end of each gradient, i.e., the line (not shown) linking a colored dot to a grey dot is the gradient axis. This representation exemplifies how MRI acquisition protocols can be designed to measure the dispersion and orientation of water molecules to generate quantitative indices of gray matter microstructure at the level of neurites with NODDI.
167167. Zhang H, Schneider T, Wheeler-Kingshott CA, Alexander DC. NODDI: practical in vivo neurite orientation dispersion and density imaging of the human brain. Neuroimage. 2012;61:1000-16.
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