Introduction: Somatosensory evoked potentials (SSEP) play a pivotal role in the diagnosis and disease monitoring of multiple sclerosis (MS). Delayed latencies are a surrogate for demyelination along the sensory aerence. This study aimed to evaluate if SSEP latencies are representative of demyelination of the brain overall, by correlating with cerebral microstructural integrity as measured by Magnetic resonance (MR) diusion tensor imaging (DTI). Analysis was performed in a hypothesis-free whole brain approach using tract-based spatial statistics (TBSS). Material and methods: A total of 46 patients with MS or clinically isolated syndrome were included in the study. Bilateral SSEPs of the median nerve measuring mean N20 latencies (mN20) and Central Conduction Time (CCT), were acquired. MRI scans were performed at 3T. DTI acquisition was done with a single-shot echoplanar imaging technique with 80 diusion directions. The FSL software package was used to process the DTI datasets and to calculate maps of fractional anisotropy (FA), axial diusivity (AD), and radial diusivity (RD). These maps were then further analyzed using the TBSS module. The mean N20 and CCT and the right- and left-sided N20 and CCT were separately correlated to FA, AD, and RD, controlled for age, gender, and EDSS as variables of non-interest. Results: Widespread negative correlations of SSEP latencies with FA (p = 0.0005) and positive correlations with RD (p = 0.0003) were measured in distinct white matter tracts, especially the optic tracts, corpus callosum, and posterior corona radiata. No correlation with AD was found in any white matter tract. Conclusion: Highly significant correlations of FA and RD to SSEPs suggest that their latency is representative of widespread microstructural change, and especially demyelination in patients suering from MS, reaching beyond the classic somatosensory regions. This points to the usefulness of SSEPs as a non-invasive tool in the evaluation of microstructural damage to the brain.

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<p>Diffusion tensor (DT) and blood oxygen-level dependent (BOLD) imaging are two noninvasive magnetic resonance (MR) techniques that have been used to probe skeletal muscle microstructure and microvasculature, respectively. Over a series of four studies, the work in this thesis aimed at furthering our understanding of baseline DT metrics and BOLD signals in lower limb muscles (calf and foot) of healthy young subjects. Since postural changes have been shown to alter numerous quantities, including fluid volumes and muscle cross sectional area, DT indices and BOLD signal characteristics were examined in response to movement from upright to supine position.</p> <p>Reductions of 3.2-6.7% and 3.4-7.5% were measured in calf DT eigenvalues and apparent diffusion coefficient (ADC) in the various muscles, following 34 and 64 minutes of supine rest, respectively (P</p> <p>Establishment of baseline diffusion metrics in the foot region was feasible (chapter 6). Examination of foot DT indices in response to positional change showed that the metrics decreased from 2.7-4.6% following 34 minutes of supine rest (P</p> / Doctor of Philosophy (PhD)

In spinal cord injury the amount of total surviving white matter is known to be strongly related to post injury neurological functions (1). Accurate segmentation of these regions is shown to be critical in terms of developing effective treatment (1). Diffusion Tensor Imaging (DTI) has been shown to be effective in obtaining spinal cord images (2). However challenges still exist in clear separation of gray/white/cerebrospinal fluid (CSF) structures within the cord using DTI. The purpose of this study is to (1) test a semi-automatic tissue segmentation algorithm based on grow cut algorithm (GCA), to classify CSF, gray and white matter in conventional T2 weighted MRI and Diffusion Tensor Imaging (DTI) images in pediatric spinal cord injury (SCI) subjects, and (2) to compare the results of semi-automatic GCA segmentation with manually segmented spinal cord data performed on various DTI images by a board certified pediatric neuroradiologist. Results show that semi-automatic segmentation of the spinal cord using GCA was successfully implemented. Qualitatively, good separation of cord/CSF was seen in B0, CFA and FA maps (of a representative patient with SCI and a control using this GCA method. They demonstrate more homogeneous signal within the cervical spinal cord as well as greater conspicuity of the cord and surrounding CSF interface. Quantitative analysis of images segmented using GCA and manual segmentation between and within the groups showed no significant differences in CFA (p=0.1347) and FA (p=0.1442) images but B0 (p=0.0001) images showed statistically significant differences. Overall, in both the controls and subjects with SCI, quantitative and qualitative analysis showed a superior semi-automated segmentation on CFA and FA images over a B0 image the using modified GCA. Key words: Grow Cut Algorithm (GCA), Magnetic Resonance Imaging (MRI), segmentation, Diffusion Tensor Imaging (DTI), cervical spinal cord, cerebral-spinal fluid (CSF). / Bioengineering

Diffusion tensor imaging (DTI) is a specialist MRI modality that can identify microstructural changes or abnormalities in the brain. It can also be used to show fibre tract pathways. Both of these features were used in this thesis. Firstly, standard imaging analysis techniques were used to study the effects of mild, repetitive closed head injury on a group of professional boxers. Such data is extremely rare, so the findings of regions of brain abnormalities in the boxers are important, adding to the body of knowledge about more severe traumatic brain injury. The author developed a novel multivariate analysis technique which was used on the same data. This new technique proved to be more sensitive than the standard univariate methods commonly used. An important part of diagnosing and monitoring brain damage involves the use of biomarkers. A novel investigation of whether diffusion parameters obtained from DTI data could serve as bio-markers of cognitive impairment in Parkinson's disease was conducted. This also involved developing a multivariate approach, which displayed increased sensitivity compared with any of the component parameters used singly, and suggested these diffusion measures could be robust bio-markers of cognitive impairment. Fibre tract connectivity between regions of the brain is also a potentially valuable measure for diagnosis and monitoring brain integrity. The feasibility of this was investigated in a multi-modal MRI study. Functional MRI (fMRI) identifies regions of activation associated with a particular task. DTI can then find the pathway of the fibre bundles connecting these regions. The feasibility of using regional connectivity to interrogate brain integrity was investigated using a single healthy volunteer. Fibre pathways between regions activated and deactivated by a working memory paradigm were determined. Though the results are only preliminary, they suggest that this line of research should be continued.

Temporomandibular disorders (TMD) are a family of prevalent chronic pain disorders affecting masticatory muscles and/or the temporomandibular joint. There is no unequivocally recognized peripheral aetiology for idiopathic TMD. The central nervous system (CNS) may initiate and/or maintain the pain in idiopathic TMD due to sustained or long-term nociceptive input that induces maladaptive brain plasticity, and/or to inherent personality-related factors that may reduce the brain's capacity to modulate nociceptive activity. The main aim of this thesis is to determine whether there are structural neural abnormalities in patients with TMD, and whether these abnormalities are related to TMD pain characteristics, or to neuroticism. The specific aims are to delineate in TMD: (1) gray matter (GM) brain abnormalities and the contribution of pain and neuroticism to abnormalities; (2) the contribution of abnormal brain GM aging in focal cortical regions associated with nociceptive processes; and (3) abnormalities in brain white matter and trigeminal nerve and the contribution of pain. In groups of 17 female patients with TMD and 17 age- and sex- matched controls, magnetic resonance imaging revealed that patients with TMD had: (1) thicker cortex in the somatosensory, ventrolateral prefrontal and frontal polar cortices than controls, (2) cortical thickness in motor and cognitive areas that was negatively related to pain intensity, orbitofrontal cortical thickness that was negatively correlated to pain unpleasantness, and thalamic GM volume correlated to TMD duration, (3) an abnormal relationship between neuroticism and orbitofrontal cortical thickness, (4) abnormal GM aging in nociceptive, modulatory and motor areas, (5) widespread abnormalities in white matter tracts in the brain related to sensory, motor and cognitive functions, (6) reduced trigeminal nerve integrity related to pain duration, and (7) abnormal connectivity in cognitive and modulatory brain regions. In sum, this thesis demonstrates for the first time abnormalities in both peripheral nerve and CNS in patients with TMD.

Temporomandibular disorders (TMD) are a family of prevalent chronic pain disorders affecting masticatory muscles and/or the temporomandibular joint. There is no unequivocally recognized peripheral aetiology for idiopathic TMD. The central nervous system (CNS) may initiate and/or maintain the pain in idiopathic TMD due to sustained or long-term nociceptive input that induces maladaptive brain plasticity, and/or to inherent personality-related factors that may reduce the brain's capacity to modulate nociceptive activity. The main aim of this thesis is to determine whether there are structural neural abnormalities in patients with TMD, and whether these abnormalities are related to TMD pain characteristics, or to neuroticism. The specific aims are to delineate in TMD: (1) gray matter (GM) brain abnormalities and the contribution of pain and neuroticism to abnormalities; (2) the contribution of abnormal brain GM aging in focal cortical regions associated with nociceptive processes; and (3) abnormalities in brain white matter and trigeminal nerve and the contribution of pain. In groups of 17 female patients with TMD and 17 age- and sex- matched controls, magnetic resonance imaging revealed that patients with TMD had: (1) thicker cortex in the somatosensory, ventrolateral prefrontal and frontal polar cortices than controls, (2) cortical thickness in motor and cognitive areas that was negatively related to pain intensity, orbitofrontal cortical thickness that was negatively correlated to pain unpleasantness, and thalamic GM volume correlated to TMD duration, (3) an abnormal relationship between neuroticism and orbitofrontal cortical thickness, (4) abnormal GM aging in nociceptive, modulatory and motor areas, (5) widespread abnormalities in white matter tracts in the brain related to sensory, motor and cognitive functions, (6) reduced trigeminal nerve integrity related to pain duration, and (7) abnormal connectivity in cognitive and modulatory brain regions. In sum, this thesis demonstrates for the first time abnormalities in both peripheral nerve and CNS in patients with TMD.

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) and DBS of the pedunculopontine nucleus (PPN) have been shown to be effective surgical therapies for Parkinson’s disease (PD). To better understand the PPN and STN as DBS targets for PD, this research compares the anatomy, electrophysiology, and motor control roles of these nuclei. PPN and STN connections were examined in vivo in human subjects and in the non-human primate using probabilistic diffusion tractography. Both the PPN and STN were connected with each other and with the motor cortex (M1) and basal ganglia. After studying these anatomical connections in primates, their functional significance was further explored in an anesthetized rat model of PD. Examination of the electrophysiological relationship between the PPN and basal ganglia in the presence of slow cortical oscillatory activity suggested that excitatory input from the STN may normally modulate PPN spike timing but that inhibitory oscillatory input from the basal ganglia output nuclei has a greater effect on PPN spike timing in the parkinsonian brain. To examine transmission and modulation of oscillatory activity between these structures at higher frequencies, LFP activity was recorded from the PPN and STN in PD patients performing simple voluntary movements. Movement-related modulation of oscillatory activity predominantly occurred in the α (8-12 Hz) and low β (12-20 Hz) frequencies in the STN but in the high β (20-35 Hz) frequencies in the PPN, supporting observations from rodent studies suggesting that oscillatory activity is not directly transmitted from the STN to the PPN in PD. Finally, to better understand the roles of the STN and PPN in large-scale movement, the effects of STN and PPN DBS on gait abnormalities in PD patients were studied. DBS of the STN appeared to improve gait by optimising executive gait control while DBS of the PPN appeared to restore autonomic gait control. These results have several implications for DBS patient selection, surgical targeting, and for understanding the mechanisms underlying DBS efficacy.

L'imagerie en tenseur de diffusion (DTI) permet de fournir un complément d'informations quantitatives au niveau tissulaire et sur le suivi des fibres de substance blanche. Elle nous a permis d'explorer chez des patients atteints d'épilepsie du lobe temporal (TLE) des anomalies cérébrales non détectables par les techniques d'imagerie conventionnelles. Dans ce travail de thèse nous avons combiné deux méthodes computationnelles s'appuyant l'une sur l'extraction d'informations dans des régions d'intérêts localisées et l'autre sur des mesures effectuées (moyennées) le long des fibres de substance blanche. L'identification de paramètres, à partir du tenseur de diffusion, a permis de mettre en évidence des modifications structurales de la substance blanche et de la substance grise, notamment au niveau des régions du système limbique (hippocampe, fornix, régions cingulaires, thalamus, amygdala). Trois groupes de sujets ont participé à cette étude : un groupe de patients atteints d'épilepsie du lobe temporal avec sclérose hippocampique (TLE+HS), un groupe de patients sans lésion visible sur l'IRM conventionnelle (TLE-HS) et un groupe de sujets volontaires. Les résultats obtenus ont montré des anomalies significatives dans les régions analysées chez les patients TLE-HS, différentes des celles retrouvées chez les patients TLE+HS. Les indices de tenseur de diffusion retenus ont permis de mettre en évidence une désorganisation structurale des régions du système limbique chez les patients TLE, spécialement dans le groupe sans lésion visible sur l'IRM conventionnelle / Diffusion tensor imaging (DTI) can provide quantitative information of brain abnormalities in patients with temporal lobe epilepsy (TLE). This technique allowed us to explore brain abnormalities that are not detectable with conventional magnetic resonance imaging (MRI).In this thesis we combined two computational methods: the first is based on information extraction from regions of interest and the second is based on measurements (averaged) along the white matter fibers. The identification of parameters from diffusion tensor has highlighted structural changes in the white matter and gray matter, particularly in the limbic system regions (hippocampus, fornix, cingulate regions, thalamus, amygdala). Three subject groups participated on this study: a patients group with temporal lobe epilepsy and a hippocampal sclerosis (TLE+HS), a patients group with TLE and normal conventional MRI (TLE-HS) and a healthy controls group. The results showed significant abnormalities in the analysed regions in patients with TLE-HS, different from those found in patients with TLE + HS. The selected diffusion tensor indices allowed us to highlight the structural disorganization of limbic system regions in patients with TLE, especially in patients with normal conventional MRI

O Transtorno de Humor Bipolar (THB) acomete até 3% dos adultos e os filhos desses pacientes constituem uma população em risco para o desenvolvimento de transtornos psiquiátricos. No entanto, faltam marcadores que permitam a identificação precoce dos indivíduos que apresentam maior vulnerabilidade para o desenvolvimento de psicopatologia. Estudos preliminares com Ressonância Magnética (RM) indicaram que alterações em substância branca estariam presentes não apenas em pacientes em episódio de alteração de humor, mas também em pacientes eutímicos e em seus familiares saudáveis, sugerindo que tais alterações poderiam constituir um endofenótipo potencial deste transtorno. A Imagem por Tensor de Difusão (Diffusion Tensor Magnetic Resonance Imaging - DT-MRI) é uma aquisição de RM que permite análise mais completa e detalhada das características da substância branca cerebral que a RM tradicional. A investigação de alterações na estrutura cerebral, particularmente de substância branca, de jovens portadores de THB não medicados e familiares saudáveis criteriosamente avaliados pode ajudar a elucidar a neurobiologia subjacente ao THB e, conseqüentemente, a identificar marcadores de vulnerabilidade ao transtorno. Objetivo: Avaliar se havia alterações em substância branca em crianças e adolescentes com THB e crianças e adolescentes filhos saudáveis de portadores de transtorno do humor bipolar quando comparados a controles saudáveis, utilizando a técnica de neuroimagem de DTMRI. Nossas hipóteses eram que jovens com THB e filhos de pacientes com THB, quando comparados a controles saudáveis, apresentariam (i) diminuição da fração de anisotropia (FA) e (ii) essas alterações seriam mais pronunciadas em crianças acometidas por THB do que em crianças saudáveis filhas de pacientes com THB. Métodos: Obtivemos imagens de DT-MRI de boa qualidade de 16 crianças e adolescentes com THB (média de idade ± D.P.= 12,7 ± 2,5 anos), 15 filhos saudáveis de pacientes com THB tipo I (média de idade ± D.P.= 13,5 ± 2,7 anos) e 15 controles saudáveis (média de idade ± D.P.= 13,5 ± 2,5 anos). Os diagnósticos foram formulados de acordo com os critérios do DSM-IV, usando as entrevistas Kiddie-SADS-PL (crianças) e Structured Clinical Interview for DSM-IV (adultos). A RM foi realizada em um scanner Philips 3,0 Tesla, com os seguintes parâmetros de aquisição: TR = 6106,0 ms, TE = 65,0ms, FOV = 224x224mm, espessura de corte = 2.0mm, sem gap, matriz de aquisição = 112x112 pixels e 3 médias, resultando em tamanho de voxel isotrópico = 2,0x2,0x2,0mm. As imagens de DTI foram pré-processadas com programas oriundos do FMRIB\'s software library (FSL), de acordo com o pipeline sugerido para o processamento de substância branca com Tract-Based Spatial Statistics (TBSS) e análise estatística com o programa Randomise (ambos integrantes do FSL). Resultados: Os grupos não diferiram em idade, gênero, grau de puberdade ou QI. Valores de FA de pacientes pediátricos com THB foram significativamente menores em relação aos de controles saudáveis (p < 0,05, corrigido para múltiplas comparações) em um cluster de 695 voxels no hemisfério direito que abrange a porção superiora da corona radiata e o corpo do corpo. Não houve diferença significativa entre pacientes com THB e filhos saudáveis de pacientes com THB, ou com filhos saudáveis de pacientes com THB e controles saudáveis. Discussão: Nossos dados corroboram a literatura de diminuição de FA em crianças e adolescentes com THB e avançam em mostrar esta alteração em pacientes não medicados. Mas nossos resultados não apoiam a hipótese de alterações em substância branca como endofenótipo de THB. Estudos de seguimento com amostras maiores e rigorosamente caracterizadas são necessários para se elucidar o papel das alterações em substância branca no THB. / Up to 3% of adults are affected with Bipolar Disorder (BD) and the offspring of these patients constitute a population at risk for the development of psychiatric disorders. Nevertheless, there are still no vulnerability markers to allow the early identification of those who are at greater risk of developing psychopathology among this population. Preliminary data indicate that white matter abnormalities may precede the disease onset and be present even in unaffected relatives - suggesting they could be further explored as an endophenotype for BD. Diffusion Tensor Magnetic Resonance Imaging (DTMRI) is an MRI acquisition that allows a thorough and detailed analysis of brain white matter characteristics. The investigation of white matter alterations in young, nonmedicated, BD patients and healthy relatives may help us understand the underlying neurobiology of BD. Objectives: evaluate white matter alterations in children at-risk and with BD using DT-MRI. Our hypothesis were that BD offspring, compared to healthy controls, would exhibit (i) reduced fractional anisotropy (FA) and (ii) these alterations would be more pronounced in children with BD than in those at-risk. Methods: We successfully scanned 16 BD patients (mean age ± S.D.= 12,7 ± 2,5 years) 15 healthy offspring with at least one parent with BD I diagnosis (mean age ± S.D.= 13,5 ± 2,7 years) and 15 healthy controls (mean age ± S.D.= 13,5 ± 2,5 years) with no history of psychiatric disorder in first-degree relatives. Psychiatric diagnosis were established according to the DSM-IV criteria, using the Kiddie-SADS-PL interview (children) and Structured Clinical Interview for DSM-IV (adults). The MRI was conducted at a 3.0 Tesla Philips scanner. Acquisition: the parameters were TR = 6106,0ms, TE = 65,0ms, FOV= 224x224mm, slice thickness = 2.0mm/no gap, matrix acquisition = 112x112 pixels, 3 averages, resulting in an isotropic voxel = 2,0x2,0x2,0 mm. DT-MRI images were preprocessed according to do FMRIB\'s software library\'s (FSL) pipeline for Tract-Based Spatial Statistics\' (TBSS) and Randomise analyses. Results: Groups did not differ in age, gender or pubertal status. Voxelwise analyses showed significant differences in FA values between BD patients and healthy controls (p < 0,05, FDR corrected for multiple comparisons) in a 695 voxels cluster comprising right corona radiata and corpus callosum . Discussion: This study was the first to evaluate a sample of non-medicated BD children and adolescents with DT-MRI and it corroborates extant literature data of lower FA in BD children compared to healthy controls. Nevertheless, our data do not support white matter alterations as an endophenotype for BD. More studies, with larger and well characterized samples are necessary to advance our understanding of the role of white matter alteration in BD.