Section: New Results

Towards microstructural based tractography

White matter tractography guided by anatomical and microstructural priors

Participants : Gabriel Girard [SCIL, Sherbrooke University, CA] , Maxime Descoteaux [SCIL, Sherbrooke University, CA] , Kevin Whittingstall [SCIL, Sherbrooke University, CA] , Rachid Deriche.

Diffusion-weighted magnetic resonance imaging is a unique imaging modality sensitive to the microscopic movement of water molecules in biological tissues. By characterizing the movement of water molecules, it is possible to infer the macroscopic neuronal pathways of the brain. The technique, so-called tractography, had become the tool of choice to study non-invasively the human brain's white matter in vivo. For instance, it has been used in neurosurgical intervention planning and in neurodegenerative diseases monitoring. In this thesis, we report biases from current tractography reconstruction and suggest methods to reduce them. We first use anatomical priors, derived from a high resolution T1-weighted image, to guide tractography. We show that knowledge of the nature of biological tissue helps tractography to reconstruct anatomically valid neuronal pathways, and reduces biases in the estimation of complex white matter regions. We then use microstructural priors, derived from the state-of-the-art diffusionweighted magnetic resonance imaging protocol, in the tractography reconstruction process. This allows tractography to follow the movement of water molecules not only along neuronal pathways, but also in a microstructurally specific environment. Thus, the tractography distinguishes more accurately neuronal pathways and reduces reconstruction errors. Moreover, it provides the mean to study white matter microstructure characteristics along neuronal pathways. Altogether, we show that anatomical and microstructural priors used during the tractography process improve brain’s white matter reconstruction

This work has been published in  [12].

Microstructure ­ driven tractography in the human brain

Participants : Gabriel Girard [SCIL, Sherbrooke University, CA] , Alessandro Daducci [SP Lab - Laboratoire de Traitement du signal, EPFL] , Kevin Whittingstall [SCIL, Sherbrooke University, CA] , Rachid Deriche, Maxime Descoteaux [SCIL, Sherbrooke University, CA] , Demian Wassermann.

Diffusion-weighted (DW) magnetic resonance imaging (MRI) tractography has become the tool of choice to probe the human brain's white matter (WM) in vivo. However, the relationship between the resulting streamlines and underlying WM microstructure characteristics, such as axon diameter, remains poorly understood. In this work, we reconstruct human brain fascicles using a new approach to trace WM fascicles while simultaneously characterizing the apparent distribution of axon diameters within the fascicle. This provides the mean to estimate the microstructure characteristics of fascicles while improving their reconstruction in complex tissue configurations.

This work has been published in  [24].

Reducing Invalid Connections with Microstructure Driven Tractography

Participants : Gabriel Girard [SCIL, Sherbrooke University, CA] , Kevin Whittingstall [SCIL, Sherbrooke University, CA] , Alessandro Daducci [SP Lab - Laboratoire de Traitement du signal, EPFL] , Jean-Philippe Thiran [SP Lab - Laboratoire de Traitement du signal, EPFL] , Laurent Petit [GIN - IMN UMR 5293 CNRS CEA Université de Bordeaux] , Rachid Deriche, Demian Wassermann, Maxime Descoteaux [SCIL, Sherbrooke University, CA] .

Diffusion-weighted imaging (DWI) tractography has become the tool of choice to probe the human brain's white matter (WM) in vivo. However, tractography algorithms produce a large number erroneous/invalid streamlines largely due to complex ambiguous local fiber configurations (e.g. crossing, kissing or fanning). Moreover, the relationship between the resulting streamlines and the underlying WM microstructure characteristics, such as axon diameter, remains poorly understood. The distinctive aspect of our tractography algorithm from previous methods is the active use of microstructure information about fascicles during the tracking. This enables us to solve areas of complex tissue configuration and separate parallel fascicles with different microstructure characteristics, hence improving the overall tractography process.

This work has been published in  [35]

Quantitative evaluation of Fiber Orientations Extractions

Participants : Thinhinane Megherbi [LRPE, USTHB, Alger] , Gabriel Girard [SCIL, Sherbrooke University, CA] , Maxime Descoteaux [SCIL, Sherbrooke University, CA] , Fatima Oulebsir Boumghar [LRPE, USTHB, Alger] , Rachid Deriche.

Recovering the fiber orientations in each voxel constitutes an important step for the fiber tracking algorithms. In fact, the reliability of the resulted connectivity depends on how well the local fiber orientations were extracted. Based on the tractography results we evaluated and compared different methods of fiber orientations extraction. Thus, we analyzed quantitatively the resulted connectivity by using the Tractometer tool. This later allows by measuring a number of metrics to quantify the connections reliability and the tractography performance. All the methods of fiber orientations extraction were evaluated on two types of tractography algorithms, deterministic and probabilistic algorithms. Furthermore, all of these methods have been executed on two types of data, high angular resolution data acquired with 60 gradient directions and low angular resolution data, acquired with 30 gradient directions. These two types of data were corrupted with a Ricien noise of ratio SNR=20, 10. In this work, we present the results obtained by our validation and comparison work.

This work has been published in  [37]