Addressing the path-length-dependency confound in white matter tract segmentation

We derive the Iterative Confidence Enhancement of Tractography (ICE-T) framework to address the problem of path-length dependency (PLD), the streamline dispersivity confound inherent to probabilistic tractography methods. We show that PLD can arise as a non-linear effect, compounded by tissue complexity, and therefore cannot be handled using linear correction methods. ICE-T is an easy-to-implement framework that acts as a wrapper around most probabilistic streamline tractography methods, iteratively growing the tractography seed regions. Tract networks segmented with ICE-T can subsequently be delineated with a global threshold, even from a single-voxel seed. We investigated ICE-T performance using ex vivo pig-brain datasets where true positives were known via in vivo tracers, and applied the derived ICE-T parameters to a human in vivo dataset. We examined the parameter space of ICE-T: the number of streamlines emitted per voxel, and a threshold applied at each iteration. As few as 20 streamlines per seed-voxel, and a robust range of ICE-T thresholds, were shown to sufficiently segment the desired tract network. Outside this range, the tract network either approximated the complete white-matter compartment (too low threshold) or failed to propagate through complex regions (too high threshold). The parameters were shown to be generalizable across seed regions. With ICE-T, the degree of both near-seed flare due to false positives, and of distal false negatives, are decreased when compared with thresholded probabilistic tractography without ICE-T. Since ICE-T only addresses PLD, the degree of remaining false-positives and false-negatives will consequently be mainly attributable to the particular tractography method employed. Given the benefits offered by ICE-T, we would suggest that future studies consider this or a similar approach when using tractography to provide tract segmentations for tract based analysis, or for brain network analysis

Exploring an avenue of Research

The phenomenon of ‘digital living’ is to a high extent influenced by the introduction of new media into society. Especially, social media are affecting the digital world of today and are setting the agenda for social connectedness in private, public and commercial networks. Based in an initial desire to explore a research agenda for the workings of social media in network structures a look into the literature on social media within the field of Information Systems sparked an interest in exploring a new research perspective for social media. Reviewing the IS literature it is apparent that the perspective of the ‘media’ as an artifact of social media has been neglected in existing literature. Based in this, this paper proposes research possibilities for investigating the ‘media’ of social media as well as some theoretical considerations that could aid the investigation. Finally, potential outcomes of pursuing the possible research area are outlined

Axonal T₂ estimation using the spherical variance of the strongly diffusion-weighted MRI signal.

In magnetic resonance imaging, the application of a strong diffusion weighting suppresses the signal contributions from the less diffusion-restricted constituents of the brain's white matter, thus enabling the estimation of the transverse relaxation time T <sub>2</sub> that arises from the more diffusion-restricted constituents such as the axons. However, the presence of cell nuclei and vacuoles can confound the estimation of the axonal T <sub>2</sub> , as diffusion within those structures is also restricted, causing the corresponding signal to survive the strong diffusion weighting. We devise an estimator of the axonal T <sub>2</sub> based on the directional spherical variance of the strongly diffusion-weighted signal. The spherical variance T <sub>2</sub> estimates are insensitive to the presence of isotropic contributions to the signal like those provided by cell nuclei and vacuoles. We show that with a strong diffusion weighting these estimates differ from those obtained using the directional spherical mean of the signal which contains both axonal and isotropically-restricted contributions. Our findings hint at the presence of an MRI-visible isotropically-restricted contribution to the signal in the white matter ex vivo fixed tissue (monkey) at 7T, and do not allow us to discard such a possibility also for in vivo human data collected with a clinical 3T system

Enterprise Social Media at Work

This PhD thesis is concerned with the social dynamics of Enterprise Social Media (ESM) at work. As ESM technologies are making their way on to the organizational scene, knowledge about how to understand and work with these media are in demand. Existing knowledge about ESM in organizations highlights the technological features and the new possibilities for organizational work that these media bring forward. However, the open and perpetual display of organizational connections and conversations on ESM also presents a unique opportunity for studying the role of social interactions and relationships that underlie organizational work on these platforms. The purpose of this PhD thesis is to examine ESM in light of its social dynamics and the implications of these for organizational work. In the context of this research, social dynamics refer to the interactions and relationships between actors in the organization. Conceptually the social dynamics of ESM at work are investigated in the light of three domains of ESM, sociality and work and their intersections. The investigation builds on the empirical setting of three organizations utilizing the ESM technology Yammer and involves the examination of the organizations’ use of the platform through methods of interviews and observations onsite and online. The thesis makes three central contributions to our understanding of the social dynamics of ESM at work. First, the thesis adds to existing perspectives on ESM in organizations by integrating the three domains of ESM, sociality and work. While the literature has so far treated these domains separately or in pairs, this research demonstrates how the social dynamics of ESM in organizations arise between the functionalities of the ESM technology, the sociality of the organizational members, and the work practices carried out. Second, the thesis presents a social fabric framework as a way of explaining, interpreting and understanding the social dynamics of ESM at work. Mapping the social fabric of the organization on ESM provides valuable insight into the dynamic and diverse nature of the relationships that form on the platform and how these create the basis of work. Third, the thesis contributes a relational constructivist perspective to the study of the social dynamics of ESM at work that emphasize the study of relationships between actors rather than the study of individual actors. Considering the social dynamics of ESM in organizations through the social fabric framework provides researchers and practitioners with a new way of understanding and theorizing about ESM at work

What Political Parties Want to Facilitate, Project and Create

In recent years, social media have become omnipresent and highly important for social networking and content sharing. Lately we have witnessed how also political parties adopt social media as part of their political campaign strategy. The purpose of this work-in-progress paper is to investigate this tendency by posing two research questions: 1) what do political parties perceive as affordances of social media use in their campaign strategy? And 2) how are these affordances reflected in the political parties’ actual actions during the campaign? To address the two questions, we conducted a qualitative case study of the political parties’ use of Facebook in the Danish general election in 2011. Our preliminary findings reveal three main categories of affordances that the political parties wish to pursue: 1) they want to facilitate direct communication to promote political interests and create room for dialogue in a controlled environment, 2) they want to project an image of authenticity through an informal media, and 3) they want to create interaction and involvement through dynamic relationships with voters. A closer look at the parties’ actual use of Facebook reveals that their intention of generating interaction and involvement is limited by their actions as most of them do not engage with the users’ posts and comments. The tensions between perceived affordances and actual use prompt further investigation of what political parties should consider when engaging in social media activities as part of their campaign strategy

Simultaneous Assessment of White Matter Changes in Microstructure and Connectedness in the Blind Brain

Magnetic resonance imaging (MRI) of the human brain has provided converging evidence that visual deprivation induces regional changes in white matter (WM) microstructure. It remains unclear how these changes modify network connections between brain regions. Here we used diffusion-weighted MRI to relate differences in microstructure and structural connectedness of WM in individuals with congenital or late-onset blindness relative to normally sighted controls. Diffusion tensor imaging (DTI) provided voxel-specific microstructural features of the tissue, while anatomical connectivity mapping (ACM) assessed the connectedness of each voxel with the rest of the brain. ACM yielded reduced anatomical connectivity in the corpus callosum in individuals with congenital but not late-onset blindness. ACM did not identify any brain region where blindness resulted in increased anatomical connectivity. DTI revealed widespread microstructural differences as indexed by a reduced regional fractional anisotropy (FA). Blind individuals showed lower FA in the primary visual and the ventral visual processing stream relative to sighted controls regardless of the blindness onset. The results show that visual deprivation shapes WM microstructure and anatomical connectivity, but these changes appear to be spatially dissociated as changes emerge in different WM tracts. They also indicate that regional differences in anatomical connectivity depend on the onset of blindness