  Diffusion magnetic resonance imaging (dMRI) tractography is an advanced
imaging technique that enables in vivo mapping of the brain's white matter
connections at macro scale. Over the last two decades, the study of brain
connectivity using dMRI tractography has played a prominent role in the
neuroimaging research landscape. In this paper, we provide a high-level
overview of how tractography is used to enable quantitative analysis of the
brain's structural connectivity in health and disease. We first provide a
review of methodology involved in three main processing steps that are common
across most approaches for quantitative analysis of tractography, including
methods for tractography correction, segmentation and quantification. For each
step, we aim to describe methodological choices, their popularity, and
potential pros and cons. We then review studies that have used quantitative
tractography approaches to study the brain's white matter, focusing on
applications in neurodevelopment, aging, neurological disorders, mental
disorders, and neurosurgery. We conclude that, while there have been
considerable advancements in methodological technologies and breadth of
applications, there nevertheless remains no consensus about the "best"
methodology in quantitative analysis of tractography, and researchers should
remain cautious when interpreting results in research and clinical
applications.
