====== Neurite orientation dispersion and density imaging ======

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[[Neurite orientation]] dispersion and density imaging (NODDI) is a [[neuroimaging]] [[technique]] that uses [[diffusion magnetic resonance imaging]] (dMRI) to measure the orientation and density of [[nerve fiber]]s in the brain.

NODDI is particularly useful for investigating the microstructure of [[white matter]], which consists of bundles of [[axon]]al [[fiber]]s that transmit information between different [[region]]s of the brain. By measuring the orientation and density of these fibers, NODDI can provide insights into the [[connectivity]] and [[organization]] of the brain's [[neural network]]s.

NODDI works by analyzing the diffusion of water molecules in brain tissue. Water molecules diffuse more easily along the direction of axonal fibers than across them, so the direction and strength of water diffusion can be used to infer the orientation and density of the fibers. NODDI also takes into account the presence of other tissue components, such as glial cells and extracellular space, which can affect water diffusion.

NODDI has many potential applications in neuroscience and clinical research. For example, it can be used to study the effects of brain injury or disease on white matter microstructure, to investigate the development of the brain during infancy and childhood, and to identify biomarkers for neurodegenerative disorders.
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More advanced diffusion MRI technology such as [[neurite orientation dispersion and density imaging]] (NODDI) could provide more sensitive and specific biomarkers of the progression from acute mTBI to chronic cognitive and behavioral impairment than is possible with DTI
((Mukherjee P, Palacios EM, Manley GT. Response to the Letter to the Editor by Dr. Michael Hutchinson re: NEU-2021-0408.R1. J Neurotrauma. 2023 Feb 28. doi: 10.1089/neu.2023.0054. Epub ahead of print. PMID: 36855321.))

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Nineteen patients with iNPH and 12 healthy controls were included. Diffusion MRI data for NODDI were acquired with a 3-T system, using 32 motion-probing gradient directions with six b-values (from 0 to 2500 s/mm2). The orientation dispersion index (ODI), intra-cellular volume fraction (Vic), and isotropic volume fraction (Viso) of the CST were calculated by tract-specific analysis in patients and controls. We also measured the fractional anisotropy (FA) and apparent diffusion coefficient (ADC).

The ODI of the CST (0.087 ± 0.024 vs. 0.183 ± 0.051, P < 0.01, Mann-Whitney U test) and Vic of the CST (0.551 ± 0.061 vs. 0.628 ± 0.038, P < 0.01, Mann-Whitney U test) were significantly lower in iNPH patients than in healthy controls. In receiver-operating characteristic analysis, the area under the curve (AUC) of the ODI and FA were not significantly different (Fig. 4a, 0.987 vs. 0.904, P = 0.061), and the AUC of the Vic and ADC also showed no significant difference (Fig. 4b, 0.864 vs. 0.912, P = 0.194).

The NODDI can effectively evaluate the condition of neurites in the CST of iNPH patients, and the ODI could be clinically useful in the diagnosis of iNPH
((Irie R, Tsuruta K, Hori M, Suzuki M, Kamagata K, Nakanishi A, Kamiya K,
Nakajima M, Miyajima M, Arai H, Aoki S. Neurite orientation dispersion and
density imaging for evaluation of corticospinal tract in idiopathic normal
pressure hydrocephalus. Jpn J Radiol. 2016 Oct 27. PubMed PMID: 27787666.
)).