Application of Diffusion Tensor Imaging to Brain Gray and White Ma er A In the present work we explore the gray and white ma er applicability of diffusion tensor imaging (DTI). To evaluate effect of ferritin-bound iron on gray ma er contrast in DTI, we created an in vitro model consisting of agarose gel phantoms doped with ferritin, and validated our results in vivo on healthy volunteer subjects - years of age in the basal ganglia. We further explored the application of DTI to amyotrophic lateral sclerosis (ALS) and multiple system atrophy (MSA); neurodegenerative diseases with gray and white ma er pathophysiological components. In the ALS study, patients and age- and sex-matched controls were recruited, while the MSA study included probable MSA subjects ( MSA-P, MSA-C) and age- and sex-matched controls. We found that ferritin-bound iron may make a signi cant contribution to DTI scalars in gray ma er regions of the brain, mediated by eigenvalue repulsion. is has important implications for DTI studies targeting gray ma er regions, especially in adolescence and in diseases associated with altered brain-iron load. In ALS, we found altered diffusion in the corona radiata and callosal body, and changes in R in the caudate nucleus and frontal white ma er. In MSA, we observed widespread white ma er changes associated...

In the early 1990s the South African automotive sector was regarded as ineffective, uncompetitive and dependent on heavy tariff protection for survival. The government’s policy support through the Motor Industry Development Programme lowered tariffs and provided strong support for exports, while the production incentives of the Automotive Production Development Programme reinforced the vision that the long-term development of the sector will best be served through considerable increases in production volumes and accelerated growth. The population consisted of the seven OEMs and the 110 First Tier Suppliers. The results indicate a difference in government support between the vulnerable and non-vulnerable suppliers. The government has shown its commitment to the future of the automotive industry by policy interventions such as the Motor Industry Development Programme and the Automotive Production Development Programme. The question arises as to what extent the government’s guarantees are keeping the domestic automotive manufacturing industry sustainable? The objective of this research was to investigate the relationship between government support and the sustainability of the South African automotive industry. The conclusion of the study is that the South African automotive industry and its suppliers would not be able to survive without continued government support. / Business Management / M. Com. (Business Management)

Introduction: Bone loss, fractures, and declining physical performance are associated with muscle atrophy and fat infiltration. Muscle structure and composition differences may be apparent between women with and without osteoporosis (OP). Purpose: To: 1) evaluate the effect of a time period spent in supine on magnetic resonance imaging (MRI) measures of muscle size and diffusion properties in young and older women; 2) assess the feasibility of applying three MRI scanning methods to evaluate macrostructural and microstructural properties of leg muscles in older women; and 3) compare musculoskeletal tissue structure and composition between older women with and without OP, and to determine the relationships between bone, muscle, fat, and physical performance. Methods: Sixteen young and older women had their legs scanned with MRI at baseline and after 30 and 60 minutes of supine resting. Feasibility of recruitment, participant tolerance to scanning, and image acquisition and analysis protocols were assessed. Thirty-five moderately active, older women with and without OP underwent MRI and peripheral quantitative computed tomography scanning of the leg and performed physical performance tests. Results: In young and older women, muscle size did not change with time spent supine, but water diffusivity decreased in some muscle regions. It is feasible to perform a single session of three MRI scanning techniques in older women. Women with and without OP had similar musculoskeletal structure that showed fat infiltration is associated with reduced bone strength and slower gait speed. Conclusions: In young and older women, muscle size is unaffected by a period of supine rest, but time spent in supine may modify water diffusivity measures. It is feasible to use a combination of MRI scanning techniques to evaluate leg muscle structure in older women. MRI improves our understanding of the relationships among muscle, fat, bone, and physical performance. / Dissertation / Doctor of Science (PhD)

Feedback is discussed in many disciplines. In behavior analysis, it has been discussed in terms of its functions, many coming to different conclusions. The present study evaluated whether therapists' preferred temporal and format of feedback shifted or changed during acquisition or maintenance of skills implementing a tact program using a token economy system after a brief exposure to all possible feedback combinations. Three participants completed a questionnaire before they were exposed to a feedback sampling phase and preferred feedback phase. Preferred way of recieving feedback was asked at the beginning of each session. Two out of three participants switched preferences after achieving mastery of task. Task mastery may make feedback delivered at the end of a session more desirable while task acquisition may make feedback delivered at the end of a trial more valuable. Limitations and future research were discussed.

En plus de la triade de symptômes caractérisant l’autisme, ce trouble neurodévelopmental est associé à des particularités perceptives et motrices et, au niveau cérébral, par une connectivité atypique entre les différentes régions du cerveau. Au niveau anatomique, un des résultats les plus communs est la réduction du corps calleux. Toutefois, des effets directs de cette altération anatomique sur l’intégrité et l’efficacité du transfert interhémisphérique restent à être démontrés. Pour la présente thèse, trois différentes études investiguent différents aspects du traitement de l’information visuomotrice : le transfert interhémisphérique entre les régions bilatérales motrices et visuelles, la vitesse de traitement perceptif, et les habiletés motrices visuellement guidées. Dans la première étude, le paradigme visuomoteur de Poffenberger a été utilisé pour mesurer le temps de transfert interhémisphérique (TTIH). L’imagerie par résonnance magnétique fonctionnelle (IRMf) et structurale ainsi que l’imagerie de diffusion ont aussi été utilisées pour étudier les réseaux cérébraux impliqués dans la tâche de Poffenberger. Les autistes ont été comparés à un groupe d’individus à développement typique. La deuxième étude avait pour but d’investiguer la vitesse de traitement perceptif en autisme. Dans la troisième étude, deux tâches motrices (Purdue et Annett) ont été utilisées pour examiner la nature et l’importance des déficits moteurs. La tâche de Purdue inclut deux conditions bimanuelles utilisées comme indice additionnel d’intégration interhémisphérique. Dans les études 2 et 3, le groupe d’autistes a aussi été comparé à un groupe d’individus Asperger afin de voir si, et comment, les deux sous-groupes peuvent être distingués en ce qui concerne le traitement visuel et les déficits moteurs. Aucune différence entre les groupes n’a été observée en termes de TTIH. Les résultats de l’étude IRMf révèlent des différences d’activations corticales en lien avec la tâche de Poffenberger. Dans les groupes d’autistes et de typiques, l’efficacité de la communication interhémisphérique était associée à différentes portions du corps calleux (frontales/motrices chez les typiques, postérieures/visuelles chez les autistes). De façon globale, les résultats de cette étude démontrent un patron atypique de transfert interhémisphérique de l’information visuomotrice en autisme, reflétant un rôle plus important des mécanismes visuels dans le comportement sensorimoteur possiblement en lien avec une réorganisation cérébrale. Les résultats des études comportementales 2 et 3 indiquent que les autistes excellent dans la tâche mesurant la vitesse de traitement perceptif alors que les Asperger accomplissent la tâche à des niveaux similaires à ceux des typiques. La nature des déficits moteurs diffère aussi entre les deux sous-groupes; la dextérité et la coordination bimanuelle est affectée chez les individus Asperger mais pas chez les autistes, qui eux sont plus atteints au niveau de la rapidité unimanuelle. Les sous-groupes d’autistes et de syndrome d’Asperger sont caractérisés par des profils cognitifs différents dont les particularités perceptives et motrices font partie intégrante. / In addition to the triad of symptoms characterizing autism, this neurodevelopmental condition is characterized by visual and motor atypicalities and, at the cerebral level, by atypical connectivity between the different brain areas. Anatomically, one of the most replicated finding is a reduction of the corpus callosum. However, evidence of a direct effect of the corpus callosum reductions on integrity and efficiency of interhemispheric transfer is lacking. Three different studies were designed to investigate different aspect of visuo-motor processing: interhemispheric transfer between bilateral motor and visual brain areas, perceptual processing speed, visually guided motor performance. In the first study, the visuo-motor Poffenberger paradigm was used to measure interhemispheric transfer time (IHTT). Structural and functional magnetic resonance imaging (fMRI) and diffusion tensor imaging (DTI) were also used to study the brain networks involved in the Poffenberger task. Autistics were compared to typically developing individuals. The second study investigates whether perceptual processing speed (Inspection Time task) is atypical in autism. In the third study, two visually-guided motor tasks (the Purdue pegboard and Annett peg moving task) were used to verify the nature and magnitude of motor deficits. The Purdue task includes two bimanual conditions used as additional measures of interhemispheric communication integrity. Moreover, in studies 2 and 3, behavioral differences between autistic and Asperger individuals were investigated in order to see if and how the two subgroups can be distinguished in terms of perceptual processing and motor deficits. No group difference was observed in terms of IHTT. The fMRI results reveal a different pattern of cortical activations associated to the Poffenberger task. In the autism and typical groups, the efficiency of interhemispheric communication was associated with different portions of the corpus callosum (frontal/premotor in typicals, posterior/visual in autistics). These results demonstrate an atypical pattern of interhemispheric visuo-motor information transfer, possibly reflecting a more prominent role of visual mechanisms guiding sensorimotor behavior in autism, related to cerebral reorganizations. Results of the behavioral studies indicate that autistics have an excellent visual processing speed while Asperger individuals performed like typicals. Motor impairments also differed between the two subgroups; dexterity and bimanual coordination was impaired in Asperger individuals but not in autistics, who presented more difficulties in unimanual conditions. Autism and Asperger subgroups are characterized by different cognitive profiles in which visual processing and motor deficits are important factors.

Die Ursache für das idiopathische Stottern ist bis zum jetzigen Zeitpunkt unbekannt. Typischerweise beginnt die Redeflussstörung im Vorschulalter. Es wird davon ausgegangen, dass 1% der Bevölkerung an Stottern leidet. Bei der Frage nach pathophysiologischen Hintergründen von Sprech- und Sprachstörungen ist der Zusammenhang zwischen einer pathologischen, funktionellen Lateralisierung und einer morphologischen Asymmetrie im Bereich von neuronalen Netzwerken der Sprachbildung bereits seit längerem Gegenstand der Forschung. Im Rahmen der vorliegenden Arbeit wurde die Lateralisierung von Sprache bei 17 stotternden Probanden und 20, im Alter entsprechenden, flüssig sprechenden Probanden untersucht. Hierbei wurde die Sprachlateralisierung mithilfe der fMRT sowohl mit einem Satz- als auch mit einem Wortgenerierungsparadigma ermittelt. Ausgehend von den in der fMRT ermittelten Sprachzentren wurde die angrenzende weiße Substanz unter Verwendung der DTI auf eine Asymmetrie hin untersucht. Im Vergleich zu der Gruppe der Normalprobanden zeigten die schwer stotternden Probanden eine Verschiebung der Indexwerte, deren endgültige Ursache offen bleibt. Gesteigerte funktionelle Aktivierung in Bereichen der rechtshemisphärischen Analoga der Sprachzentren scheint ein möglicher Erklärungsansatz. Vorausgegangene funktionelle Untersuchungen u. a. mittels PET und fMRT bei stotternden Probanden belegten eine Überaktivierung von Teilen des motorischen Kortex sowie eine atypische Lateralisierung bei der Produktion von Sprache mit rechtsseitiger Lateralisierung oder eine bilaterale Aktivität. Darüber hinaus zeigte sich eine morphologische Veränderung, im Sinne einer Abnahme einer linkshemisphärischen Asymmetrie bei den schwer stotternden Probanden, besonders in der an das Wernicke-Areal angrenzenden weißen Substanz. Mithilfe der VBM konnten in mehreren früheren Studien morphologische Unterschiede bei Stotternden gezeigt werden. Gegenüber dem rein morphologischen Untersuchungsansatz vorangegangener Untersuchungen berücksichtigte die Kombination der funktionellen und der diffusionsgewichteten Analyse stärker die intraindividuelle Variabilität der Sprachzentren.

Abstract in English below.

Diffusion Tensor Imaging (DTI) is a new magnetic resonance imaging modality capable of producing quantitative maps of microscopic natural displacements of water molecules that occur in brain tissues as part of the physical diffusion process. This technique has become a powerful tool in the investigation of brain structure and function because it allows for in vivo measurements of white matter fiber orientation. The application of DTI in clinical practice requires specialized processing and visualization techniques to extract and represent acquired information in a comprehensible manner. Tracking techniques are used to infer patterns of continuity in the brain by following in a step-wise mode the path of a set of particles dropped into a vector field. In this way, white matter fiber maps can be obtained. / La imatge amb tensor de difusió (DTI) és una nova modalitat de ressonància magnètica capaç de generar mapes del desplaçament a nivell microscòpic de l’aigua a dins del teixits del cervell com a part del procés físic de la difusió. Aquesta tècnica ha esdevingut una important eina en la investigació de les estructures i funcions cerebrals perquè ens permet tenir dades in vivo de l’orientació de les fibres de matèria blanca. Per aplicar el DTI en la pràctica clínica cal extreure i representar la informació de forma entenedora aplicant tècniques i processos de visualització especialitzats. Es poden utilitzar tècniques de tractografia per tal de trobar patrons de continuïtat dins del cervell, a partir de fer el seguiment pas a pas del camí seguit per un conjunt de partícules que es deixen en un camp vectorial. D’aquesta forma és com s’obtenen els mapes de fibres de matèria blanca.

Diffusion Tensor MRI can be used to depict the anisotropy of tissue. Translation of this technique to moving objects such as the beating heart has recently become feasible, but remains a challenging task, often leading to high noise levels and limited accuracy. Ultimately, knowledge of the 3D fibre architecture of the myocardium invivo should allow for a better understanding of the cardiac function both in healthy and pathological situations. The main goal of the work presented in this thesis is to overcome the difficulties that such technology presents, by introducing a combination of image processing and analysis approaches. In particular, the characteristic ellipsoidal shape of the left ventricular chamber is used to introduce a shape-based prolate spheroidal coordinate frame that allows for comprehensive, robust and dedicated analysis of diffusion tensor data within the myocardial wall. It is shown that the description of this information is more compact in this coordinate frame. Furthermore, it is demonstrated that the acquisition limitations can be overcome by introducing an approximation scheme based on this coordinate frame. These techniques are tested on ex-vivo datasets to assess their fidelity and sensitivity. Finally, these techniques are applied in-vivo on a group of healthy volunteers, where 2D DTI slices of the LV were acquired at end diastole and end systole, using cardiac dedicated diffusion MR acquisition. Results demonstrate the advantages of using curvilinear coordinates both for the analysis and the approximation of cardiac DTI information. Resulting in-vivo fibre architectures were found to agree with previously reported studies on ex-vivo specimens. The outcome of this work can open the door for clinical applications and cardiac electrophysiology modelling, and improve the understanding of the left ventricular structure and dynamics.

Diffusion Tensor Imaging (DTI) is a well-established magnetic resonance technique that can non-invasively interpret tissue geometry and track neural pathways by sampling the diffusion of water molecules in the brain tissue. However, it is currently limited to tracking large nerve fiber bundles and fails to faithfully resolve thinner fibers. Conventional DTI studies use a diffusion time, t[subscript diff] of 30 ms - 55 ms for diffusion measurements. This work proposes the use of DTI at long t[subscript diff] to enhance the sensitivity of the method towards regions of low diffusion anisotropy and improve tracking of smaller fibers. The Stimulated Echo Acquisition Mode (STEAM) sequence was modified to allow DTI measurements at long t[subscript diff] (approximately 200 ms), while avoiding T2 signal loss. For comparison, DTI data was acquired using STEAM at the shorter value of t[subscript diff] and with the standard Double Spin Echo sequence with matched signal-to-noise ratio. This approach was tested on phantoms and fixed monkey brains and then translated to in vivo studies in rhesus macaques. Qualitative and quantitative comparison of the techniques was based on fractional anisotropy, diffusivity, three-phase plots and directional entropy. Tensor-field maps and probabilistic connectivity fronts were evaluated for all three acquisitions. Comparison of the tracked nerve pathways showed that fibers obtained at long t[subscript diff] were much longer. Further, the optic tract was tracked in ex vivo fixed rhesus brains for cross validation. The optic tract, traced at long t[subscript diff], conformed to the well documented anatomical description, thus confirming the accuracy of tract tracing at long t[subscript diff]. The benefits of DTI at long t[subscript diff] indeed help to realize the potential of tensor based tractography towards studying neural development and diagnosing neuro-pathologies, albeit the improvement is more significant ex vivo than in vivo.