"Single-Shell NODDI using Dictionary-Learner-Estimated Isotropic Volume Fraction"

Congratulations to PhD candidate Abrar Faiyaz and Professor Marvin Doyley on the publication of the journal article titled "Single-shell NODDI using dictionary-learner-estimated isotropic volume fraction." Co-authors include Drs. Giovanni Schifitto, Jianhui Zhong, and Md Nasir Uddin from the URMC Department of Neurology. This article appears in in NMR in Biomedicine. The abstract appears below and more information can be found here.

Abstract: Neurite orientation dispersion and density imaging (NODDI) enables the assessment of intracellular, extracellular, and free water signals from multi-shell diffusion MRI data. It is an insightful approach to characterize brain tissue microstructure. Singleshell reconstruction for NODDI parameters has been discouraged in previous studies caused by failure when fitting, especially for the neurite density index (NDI). Here, we investigated the possibility of creating robust NODDI parameter maps with single-shell data, using the isotropic volume fraction (f_ISO) as a prior. Prior estimation was made independent of the NODDI model constraint using a dictionary learning approach. First, we used a stochastic sparse dictionary-based network (DictNet), which is trained with data obtained from in vivo and simulated diffusion MRI data, to predict f_ISO. In single-shell cases, the mean diffusivity and raw T₂ signal with no diffusion weighting (S₀) was incorporated in the dictionary for the fISO estimation. Then, the NODDI framework was used with the known f_ISO to estimate the NDI and orientation dispersion index (ODI). The fISO estimated using our model was compared with other f_ISO estimators in the simulation. Further, using both synthetic data simulation
and human data collected on a 3 T scanner (both high-quality HCP and clinical dataset), we compared the performance of our dictionary-based learning prior NODDI (DLpN) with the original NODDI for both single-shell and multi-shell data. Our results suggest that DLpN-derived NDI and ODI parameters for single-shell protocols are comparable with original multi-shell NODDI, and the protocol with b = 2000 s/mm² performs the best (error ~ 5% in white and gray matter). This may allow NODDI evaluation of studies on single-shell data by multi-shell scanning of two subjects for DictNet f_ISO training.