Beyond crossing fibers: bootstrap probabilistic tractography using complex subvoxel fiber geometries.

Parya Momayyezsiahkal,Kaleem Siddiqi,Peter Savadjiev,G Bruce Pike,Ilana R Leppert,Jennifer S W Campbell

doi:10.3389/fneur.2014.00216

Abstract

Diffusion magnetic resonance imaging fiber tractography is a powerful tool for investigating human white matter connectivity in vivo. However, it is prone to false positive and false negative results, making interpretation of the tractography result difficult. Optimal tractography must begin with an accurate description of the subvoxel white matter fiber structure, includes quantification of the uncertainty in the fiber directions obtained, and quantifies the confidence in each reconstructed fiber tract. This paper presents a novel and comprehensive pipeline for fiber tractography that meets the above requirements. The subvoxel fiber geometry is described in detail using a technique that allows not only for straight crossing fibers but for fibers that curve and splay. This technique is repeatedly performed within a residual bootstrap statistical process in order to efficiently quantify the uncertainty in the subvoxel geometries obtained. A robust connectivity index is defined to quantify the confidence in the reconstructed connections. The tractography pipeline is demonstrated in the human brain.

Highlights

This paper describes a pipeline for performing fiber tractography using a complex description of the subvoxel fiber geometry within a bootstrap probabilistic framework
The region of interest (ROI) is at the decussation of the thalamo-cortical tract, projections of the corpus callosum, and superior longitudinal fasciculus; double and triple crossings of these fibers are seen, with the superior longitudinal fasciculus going through plane
For major fiber tracts (i.e., fractional anisotropy (FA) >0.3), the correspondence between the observed variability in the fiber orientation distribution function (ODF) maxima and the variability predicted by the bootstrap was very good, with the www.frontiersin.org percentages matching closely

Summary

Introduction

This paper describes a pipeline for performing fiber tractography using a complex description of the subvoxel fiber geometry within a bootstrap probabilistic framework. A curve inference algorithm that can accurately describe the fiber geometry of straight, crossing, bending, and fanning fibers on a subvoxel scale is examined Given this probabilistic description of the subvoxel fiber geometry, confidences are assigned to individual fiber tract segments and subsequently to entire reconstructed tracts, using a weakest link connectivity measure. While DTI was the first successful technique in modeling the diffusion PDF, it fails to extract the true fiber structure within a voxel containing a crossing, branching, or merging configuration of fibers due to its underlying assumption of a single anisotropic Gaussian PDF Using the latter techniques, a high angular resolution diffusion orientation distribution function (ODF) can be obtained, which has the potential to model multiple fiber orientations within a voxel. The fiber ODF can be calculated directly by deconvolution of the MRI signal profile with the single fiber response function in signal space [e.g., Ref. [27]], or by calculating a diffusion ODF with q-space techniques and deconvolving with the single fiber response function in diffusion ODF space [e.g., Ref. [8]]

Methods

Results

Conclusion