Quantitative streamlines tractography: methods and inter-subject normalisation

Abstract

Recent developments in semi-global tractogram optimisation algorithms have opened the field of diffusion magnetic resonance imaging (MRI) to the possibility of performing quantitative assessment of structural fibre ‘connectivity’. The proper application of these methods in neuroscience research has, however, been limited by a lack of awareness, understanding, or appreciation for the consequences of these methods; furthermore, particular steps necessary to use these tools in an appropriate manner to fully exploit their quantitative properties have not yet been described. This article therefore serves three purposes: to increase awareness of the fact that there are existing tools that attempt to address the well-known non-quantitative nature of streamlines counts; to illustrate why these algorithms work the way they do to yield quantitative estimates of white matter ‘connectivity’ (in the form of total intra-axonal cross-sectional area: ‘fibre bundle capacity (FBC)’); and to explain how to properly utilise these results for quantitative tractography analysis across subjects.