Overview
MRtrix3 is a comprehensive, open-source software suite designed for the processing and analysis of diffusion-weighted MRI (dMRI) data. Built on a modular C++ framework, it is engineered for high performance and scalability in neuroimaging research. As of 2026, it remains the premier platform for Constrained Spherical Deconvolution (CSD), allowing researchers to resolve multiple fiber orientations within a single voxel—a critical requirement for high-angular resolution diffusion imaging (HARDI). The software is particularly renowned for its implementation of Anatomically-Constrained Tractography (ACT) and Spherical-deconvolution Informed Filtering of Tractograms (SIFT/SIFT2), which address the inherent biases in tractography to provide biologically accurate connectivity estimates. Its architecture supports a wide array of formats (NIfTI, DICOM, and the native MIF format) and integrates deeply with high-performance computing environments. MRtrix3 also pioneers 'Fixel-Based Analysis' (FBA), a framework for conducting statistical inference on sub-voxel fiber populations, effectively bridges the gap between macro-scale tractography and micro-scale fiber density measurements.