Validation of NODDI estimation of dispersion anisotropy in V1 of the human neocortex

Purpose: This work presents a validation of estimating dispersion anisotropy of neurites, using Bingham-NODDI [1]. Bingham-NODDI is a recent development of the diffusion MRI (d-MRI) technique called NODDI (neurite orientation dispersion and 3 density imaging) [2]. NODDI enables mapping of the morphology of neurites (axons and 0.7 dendrites) in the brain with indices that are sensitive and specific to the microstructural changes, resulting in a rapid uptake of NODDI in the field of neuroimaging [3,4]. But the β DAI original NODDI technique, Watson-NODDI, is limited, as it constrains the orientation 0 0 dispersion of neurites to be isotropic. Bingham-NODDI was developed to address this limitation and enables estimation of dispersion anisotropy and the primary dispersion (a) (b) orientation, along with the standard NODDI indices, without imposing any additional acquisition requirements compared to the Watson-NODDI. Dispersion anisotropy is widespread in the human brain [5]; its estimation is a potential biomarker [6] and can enhance the accuracy of tractography algorithms [7]. The in vivo feasibility of the Bingham-NODDI metrics has been evaluated in [1], but the estimates obtained need to be validated. Here we conduct such a validation study using high-resolution ex-vivo imaging data, acquired on post-mortem samples of the human primary visual cortex (V1). V1 is a very well characterised region of the neocortex, with a Watson-NODDI Bingham-NODDI diverse cytoarchitecture including fibres fanning/bending into the cortical layers, making it attractive for validating the measures from Bingham-NODDI. We hypothesise that using 4 Bingham-NODDI will enable a more detailed differentiation of these characteristics and explain the data better compared to Watson-NODDI.