520 research outputs found
PRINCIPLES OF INFORMATION PROCESSING IN NEURONAL AVALANCHES
How the brain processes information is poorly understood. It has been suggested that the imbalance of excitation and inhibition (E/I) can significantly affect information processing in the brain. Neuronal avalanches, a type of spontaneous activity recently discovered, have been ubiquitously observed in vitro and in vivo when the cortical network is in the E/I balanced state. In this dissertation, I experimentally demonstrate that several properties regarding information processing in the cortex, i.e. the entropy of spontaneous activity, the information transmission between stimulus and response, the diversity of synchronized states and the discrimination of external stimuli, are optimized when the cortical network is in the E/I balanced state, exhibiting neuronal avalanche dynamics. These experimental studies not only support the hypothesis that the cortex operates in the critical state, but also suggest that criticality is a potential principle of information processing in the cortex. Further, we study the interaction structure in population neuronal dynamics, and discovered a special structure of higher order interactions that are inherent in the neuronal dynamics
Connectivity Analysis in EEG Data: A Tutorial Review of the State of the Art and Emerging Trends
Understanding how different areas of the human brain communicate with each other is a crucial issue in neuroscience. The concepts of structural, functional and effective connectivity have been widely exploited to describe the human connectome, consisting of brain networks, their structural connections and functional interactions. Despite high-spatial-resolution imaging techniques such as functional magnetic resonance imaging (fMRI) being widely used to map this complex network of multiple interactions, electroencephalographic (EEG) recordings claim high temporal resolution and are thus perfectly suitable to describe either spatially distributed and temporally dynamic patterns of neural activation and connectivity. In this work, we provide a technical account and a categorization of the most-used data-driven approaches to assess brain-functional connectivity, intended as the study of the statistical dependencies between the recorded EEG signals. Different pairwise and multivariate, as well as directed and non-directed connectivity metrics are discussed with a pros-cons approach, in the time, frequency, and information-theoretic domains. The establishment of conceptual and mathematical relationships between metrics from these three frameworks, and the discussion of novel methodological approaches, will allow the reader to go deep into the problem of inferring functional connectivity in complex networks. Furthermore, emerging trends for the description of extended forms of connectivity (e.g., high-order interactions) are also discussed, along with graph-theory tools exploring the topological properties of the network of connections provided by the proposed metrics. Applications to EEG data are reviewed. In addition, the importance of source localization, and the impacts of signal acquisition and pre-processing techniques (e.g., filtering, source localization, and artifact rejection) on the connectivity estimates are recognized and discussed. By going through this review, the reader could delve deeply into the entire process of EEG pre-processing and analysis for the study of brain functional connectivity and learning, thereby exploiting novel methodologies and approaches to the problem of inferring connectivity within complex networks
Graph-Based Network Analysis of Resting-State Functional MRI
In the past decade, resting-state functional MRI (R-fMRI) measures of brain activity have attracted considerable attention. Based on changes in the blood oxygen level-dependent signal, R-fMRI offers a novel way to assess the brain's spontaneous or intrinsic (i.e., task-free) activity with both high spatial and temporal resolutions. The properties of both the intra- and inter-regional connectivity of resting-state brain activity have been well documented, promoting our understanding of the brain as a complex network. Specifically, the topological organization of brain networks has been recently studied with graph theory. In this review, we will summarize the recent advances in graph-based brain network analyses of R-fMRI signals, both in typical and atypical populations. Application of these approaches to R-fMRI data has demonstrated non-trivial topological properties of functional networks in the human brain. Among these is the knowledge that the brain's intrinsic activity is organized as a small-world, highly efficient network, with significant modularity and highly connected hub regions. These network properties have also been found to change throughout normal development, aging, and in various pathological conditions. The literature reviewed here suggests that graph-based network analyses are capable of uncovering system-level changes associated with different processes in the resting brain, which could provide novel insights into the understanding of the underlying physiological mechanisms of brain function. We also highlight several potential research topics in the future
Artificial Intelligence for the Detection of Focal Cortical Dysplasia: Challenges in Translating Algorithms into Clinical Practice
Focal cortical dysplasias (FCDs) are malformations of cortical development and one of the most common pathologies causing pharmacoresistant focal epilepsy. Resective neurosurgery yields high success rates, especially if the full extent of the lesion is correctly identified and completely removed. The visual assessment of magnetic resonance imaging does not pinpoint the FCD in 30%–50% of cases, and half of all patients with FCD are not amenable to epilepsy surgery, partly because the FCD could not be sufficiently localized. Computational approaches to FCD detection are an active area of research, benefitting from advancements in computer vision. Automatic FCD detection is a significant challenge and one of the first clinical grounds where the application of artificial intelligence may translate into an advance for patients' health. The emergence of new methods from the combination of health and computer sciences creates novel challenges. Imaging data need to be organized into structured, well-annotated datasets and combined with other clinical information, such as histopathological subtypes or neuroimaging characteristics. Algorithmic output, that is, model prediction, requires a technically correct evaluation with adequate metrics that are understandable and usable for clinicians. Publication of code and data is necessary to make research accessible and reproducible. This critical review introduces the field of automatic FCD detection, explaining underlying medical and technical concepts, highlighting its challenges and current limitations, and providing a perspective for a novel research environment
Towards Accurate Forecasting of Epileptic Seizures: Artificial Intelligence and Effective Connectivity Findings
L’épilepsie est une des maladies neurologiques les plus fréquentes, touchant près d’un
pourcent de la population mondiale. De nos jours, bien qu’environ deux tiers des patients
épileptiques répondent adéquatement aux traitements pharmacologiques, il reste qu’un tiers des
patients doivent vivre avec des crises invalidantes et imprévisibles. Quoique la chirurgie
d’épilepsie puisse être une autre option thérapeutique envisageable, le recours à la chirurgie de
résection demeure très faible en partie pour des raisons diverses (taux de réussite modeste, peur
des complications, perceptions négatives). D’autres avenues de traitement sont donc souhaitables.
Une piste actuellement explorĂ©e par des groupes de chercheurs est de tenter de prĂ©dire les crises Ă
partir d’enregistrements de l’activité cérébrale des patients. La capacité de prédire la survenue de
crises permettrait notamment aux patients, aidants naturels ou personnels médical de prendre des
mesures de précaution pour éviter les désagréments reliés aux crises voire même instaurer un
traitement pour les faire avorter. Au cours des dernières années, d’importants efforts ont été
déployés pour développer des algorithmes de prédiction de crises et d’en améliorer les
performances.
Toutefois, le manque d’enregistrements électroencéphalographiques intracrâniens (iEEG) de
longue durée de qualité, la quantité limitée de crises, ainsi que la courte durée des périodes
interictales constituaient des obstacles majeurs à une évaluation adéquate de la performance des
algorithmes de prédiction de crises. Récemment, la disponibilité en ligne d’enregistrements iEEG
continus avec échantillonnage bilatéral (des deux hémisphères) acquis chez des chiens atteints
d’épilepsie focale à l’aide du dispositif de surveillance ambulatoire implantable NeuroVista a
partiellement facilité cette tâche. Cependant, une des limitations associées à l’utilisation de ces
données durant la conception d’un algorithme de prédiction de crises était l’absence
d’information concernant la zone exacte de début des crises (information non fournie par les
gestionnaires de cette base de données en ligne). Le premier objectif de cette thèse était la mise
en oeuvre d’un algorithme précis de prédiction de crises basé sur des enregistrements iEEG canins
de longue durée. Les principales contributions à cet égard incluent une localisation quantitative
de la zone d’apparition des crises (basée sur la fonction de transfert dirigé –DTF), l’utilisation
d’une nouvelle fonction de coût via l’algorithme génétique proposé, ainsi qu’une évaluation
quasi-prospective des performances de prédiction (données de test d’un total de 893 jours). Les résultats ont montré une amélioration des performances de prédiction par rapport aux études
antérieures, atteignant une sensibilité moyenne de 84.82 % et un temps en avertissement de 10 %.
La DTF, utilisée précédemment comme mesure de connectivité pour déterminer le réseau
épileptique (objectif 1), a été préalablement validée pour quantifier les relations causales entre les
canaux lorsque les exigences de quasi-stationnarité sont satisfaites. Ceci est possible dans le cas
des enregistrements canins en raison du nombre relativement faible de canaux. Pour faire face
aux exigences de non-stationnarité, la fonction de transfert adaptatif pondérée par le spectre
(Spectrum weighted adaptive directed transfer function - swADTF) a été introduit en tant qu’une
version variant dans le temps de la DTF. Le second objectif de cette thèse était de valider la
possibilité d’identifier les endroits émetteurs (ou sources) et récepteurs d’activité épileptiques en
appliquant la swADTF sur des enregistrements iEEG de haute densité provenant de patients
admis pour évaluation pré-chirurgicale au CHUM. Les générateurs d’activité épileptique étaient
dans le volume réséqué pour les patients ayant des bons résultats post-chirurgicaux alors que
différents foyers ont été identifiés chez les patients ayant eu de mauvais résultats postchirurgicaux.
Ces résultats démontrent la possibilité d’une identification précise des sources et
récepteurs d’activités épileptiques au moyen de la swADTF ouvrant la porte à la possibilité d’une
meilleure sélection d’électrodes de manière quantitative dans un contexte de développement
d’algorithme de prédiction de crises chez l’humain.
Dans le but d’explorer de nouvelles avenues pour la prédiction de crises épileptiques, un
nouveau précurseur a aussi été étudié combinant l’analyse des spectres d’ordre supérieur et les
réseaux de neurones artificiels (objectif 3). Les résultats ont montré des différences
statistiquement significatives (p<0.05) entre l’état préictal et l’état interictal en utilisant chacune
des caractéristiques extraites du bi-spectre. Utilisées comme entrées à un perceptron multicouche,
l’entropie bispectrale normalisée, l’entropie carré normalisée, et la moyenne ont atteint des
précisions respectives de 78.11 %, 72.64% et 73.26%.
Les résultats de cette thèse confirment la faisabilité de prédiction de crises à partir
d’enregistrements d’électroencéphalographie intracrâniens. Cependant, des efforts
supplémentaires en termes de sélection d’électrodes, d’extraction de caractéristiques, d’utilisation
des techniques d’apprentissage profond et d’implémentation Hardware, sont nécessaires avant
l’intégration de ces approches dans les dispositifs implantables commerciaux.----------ABSTRACT
Epilepsy is a chronic condition characterized by recurrent “unpredictable” seizures. While
the first line of treatment consists of long-term drug therapy about one-third of patients are said to
be pharmacoresistant. In addition, recourse to epilepsy surgery remains low in part due to
persisting negative attitudes towards resective surgery, fear of complications and only moderate
success rates. An important direction of research is to investigate the possibility of predicting
seizures which, if achieved, can lead to novel interventional avenues.
The paucity of intracranial electroencephalography (iEEG) recordings, the limited number of
ictal events, and the short duration of interictal periods have been important obstacles for an
adequate assessment of seizure forecasting. More recently, long-term continuous bilateral iEEG
recordings acquired from dogs with naturally occurring focal epilepsy, using the implantable
NeuroVista ambulatory monitoring device have been made available on line for the benefit of
researchers. Still, an important limitation of these recordings for seizure-prediction studies was
that the seizure onset zone was not disclosed/available. The first objective of this thesis was to
develop an accurate seizure forecasting algorithm based on these canine ambulatory iEEG
recordings. Main contributions include a quantitative, directed transfer function (DTF)-based,
localization of the seizure onset zone (electrode selection), a new fitness function for the
proposed genetic algorithm (feature selection), and a quasi-prospective assessment of seizure
forecasting on long-term continuous iEEG recordings (total of 893 testing days). Results showed
performance improvement compared to previous studies, achieving an average sensitivity of
84.82% and a time in warning of 10 %.
The DTF has been previously validated for quantifying causal relations when quasistationarity
requirements are met. Although such requirements can be fulfilled in the case of
canine recordings due to the relatively low number of channels (objective 1), the identification of
stationary segments would be more challenging in the case of high density iEEG recordings. To
cope with non-stationarity issues, the spectrum weighted adaptive directed transfer function
(swADTF) was recently introduced as a time-varying version of the DTF. The second objective
of this thesis was to validate the feasibility of identifying sources and sinks of seizure activity
based on the swADTF using high-density iEEG recordings of patients admitted for pre-surgical monitoring at the CHUM. Generators of seizure activity were within the resected volume for
patients with good post-surgical outcomes, whereas different or additional seizure foci were
identified in patients with poor post-surgical outcomes. Results confirmed the possibility of
accurate identification of seizure origin and propagation by means of swADTF paving the way
for its use in seizure prediction algorithms by allowing a more tailored electrode selection.
Finally, in an attempt to explore new avenues for seizure forecasting, we proposed a new
precursor of seizure activity by combining higher order spectral analysis and artificial neural
networks (objective 3). Results showed statistically significant differences (p<0.05) between
preictal and interictal states using all the bispectrum-extracted features. Normalized bispectral
entropy, normalized squared entropy and mean of magnitude, when employed as inputs to a
multi-layer perceptron classifier, achieved held-out test accuracies of 78.11%, 72.64%, and
73.26%, respectively.
Results of this thesis confirm the feasibility of seizure forecasting based on iEEG recordings;
the transition into the ictal state is not random and consists of a “build-up”, leading to seizures.
However, additional efforts in terms of electrode selection, feature extraction, hardware and deep
learning implementation, are required before the translation of current approaches into
commercial devices
Interictal Network Dynamics in Paediatric Epilepsy Surgery
Epilepsy is an archetypal brain network disorder. Despite two decades of research
elucidating network mechanisms of disease and correlating these with outcomes, the clinical
management of children with epilepsy does not readily integrate network concepts. For
example, network measures are not used in presurgical evaluation to guide decision making
or surgical management plans.
The aim of this thesis was to investigate novel network frameworks from the perspective of
a clinician, with the explicit aim of finding measures that may be clinically useful and
translatable to directly benefit patient care. We examined networks at three different scales,
namely macro (whole brain diffusion MRI), meso (subnetworks from SEEG recordings) and
micro (single unit networks) scales, consistently finding network abnormalities in children
being evaluated for or undergoing epilepsy surgery. This work also provides a path to clinical
translation, using frameworks such as IDEAL to robustly assess the impact of these new
technologies on management and outcomes.
The thesis sets up a platform from which promising computational technology, that utilises
brain network analyses, can be readily translated to benefit patient care
The effect of using multiple connectivity metrics in brain Functional Connectivity studies
Tese de mestrado integrado, Engenharia BiomĂ©dica e BiofĂsica (Sinais e Imagens MĂ©dicas) Universidade de Lisboa, Faculdade de CiĂŞncias, 2022Resting-state functional magnetic resonance imaging (rs-fMRI) has the potential to assist as a
diagnostic or prognostic tool for a diverse set of neurological and neuropsychiatric disorders, which are
often difficult to differentiate. fMRI focuses on the study of the brain functional Connectome, which is
characterized by the functional connections and neuronal activity among different brain regions, also
interpreted as communications between pairs of regions. This Functional Connectivity (FC) is quantified
through the statistical dependences between brain regions’ blood-oxygen-level-dependent (BOLD)
signals time-series, being traditionally evaluated by correlation coefficient metrics and represented as
FC matrices. However, several studies underlined limitations regarding the use of correlation metrics to
fully capture information from these signals, leading investigators towards different statistical metrics
that would fill those shortcomings. Recently, investigators have turned their attention to Deep Learning
(DL) models, outperforming traditional Machine Learning (ML) techniques due to their ability to
automatically extract relevant information from high-dimensional data, like FC data, using these models
with rs-fMRI data to improve diagnostic predictions, as well as to understand pathological patterns in
functional Connectome, that can lead to the discovery of new biomarkers. In spite of very encouraging
performances, the black-box nature of DL algorithms makes difficult to know which input information
led the model to a certain prediction, restricting its use in clinical settings.
The objective of this dissertation is to exploit the power of DL models, understanding how FC
matrices created from different statistical metrics can provide information about the brain FC, beyond
the conventionally used correlation family. Two publicly available datasets where studied, the ABIDE I dataset, composed by healthy and autism spectrum disease (ASD) individuals, and the ADHD-200
dataset, with typically developed controls and individuals with attention-deficit/hyperactive disorder
(ADHD). The computation of the FC matrices of both datasets, using different statistical metrics, was
performed in MATLAB using MULAN’s toolbox functions, encompassing the correlation coefficient,
non-linear correlation coefficient, mutual information, coherence and transfer entropy. The
classification of FC data was performed using two DL models, the improved ConnectomeCNN model
and the innovative ConnectomeCNN-Autoencoder model. Moreover, another goal is to study the effect
of a multi-metric approach in classification performances, combining multiple FC matrices computed
from the different statistical metrics used, as well as to study the use of Explainable Artificial
Intelligence (XAI) techniques, namely Layer-wise Relevance Propagation method (LRP), to surpass the
black-box problem of DL models used, in order to reveal the most important brain regions in ADHD.
The results show that the use of other statistical metrics to compute FC matrices can be a useful
complement to the traditional correlation metric methods for the classification between healthy subjects
and subjects diagnosed with ADHD and ASD. Namely, non-linear metrics like h2 and mutual
information, achieved similar and, in some cases, even slightly better performances than correlation
methods. The use of FC multi-metric, despite not showing improvements in classification performance
compared to the best individual method, presented promising results, namely the ability of this approach
to select the best features from all the FC matrices combined, achieving a similar performance in relation
to the best individual metric in each of the evaluation measures of the model, leading to a more complete
classification. The LRP analysis applied to ADHD-200 dataset proved to be promising, identifying brain
regions related to the pathophysiology of ADHD, which are in broad accordance with FC and structural
study’s findings.A ressonância magnética funcional em estado de repouso (rs-fMRI) tem o potencial de ser uma
ferramenta auxiliar de diagnĂłstico ou prognĂłstico para um conjunto diversificado de distĂşrbios
neurolĂłgicos e neuropsiquiátricos, que muitas vezes sĂŁo difĂceis de diferenciar. A análise de dados de
rs-fMRI recorre muitas vezes ao conceito de conectoma funcional do cérebro, que se caracteriza pelas
conexões funcionais entre as diferentes regiões do cérebro, sendo estas conexões interpretadas como
comunicações entre diferentes pares de regiões cerebrais. Esta conectividade funcional é quantificada
atravĂ©s de dependĂŞncias estatĂsticas entre os sinais fMRI das regiões cerebrais, sendo estas
tradicionalmente calculadas através da métrica coeficiente de correlação, e representadas através de
matrizes de conectividade funcional. No entanto, vários estudos demonstraram limitações em relação ao
uso de métricas de correlação, em que estas não conseguem capturar por completo todas as informações
presentes nesses sinais, levando os investigadores Ă procura de diferentes mĂ©tricas estatĂsticas que
pudessem preencher essas lacunas na obtenção de informações mais completas desses sinais.
O estudo destes distúrbios neurológicos e neuropsiquiátricos começou por se basear em técnicas
como mapeamento paramĂ©trico estatĂstico, no contexto de estudos de fMRI baseados em tarefas. PorĂ©m,
essas técnicas apresentam certas limitações, nomeadamente a suposição de que cada região cerebral atua
de forma independente, o que não corresponde ao conhecimento atual sobre o funcionamento do cérebro.
O surgimento da rs-fMRI permitiu obter uma perspetiva mais global e deu origem a uma vasta literatura
sobre o efeito de patologias nos padrões de conetividade em repouso, incluindo tentativas de diagnóstico
automatizado com base em biomarcadores extraĂdos dos conectomas. Nos Ăşltimos anos, os
investigadores voltaram a sua atenção para técnicas de diferentes ramos de Inteligência Artificial, mais
propriamente para os algoritmos de Deep Learning (DL), uma vez que sĂŁo capazes de superar os
algoritmos tradicionais de Machine Learning (ML), que foram aplicados a estes estudos numa fase
inicial, devido à sua capacidade de extrair automaticamente informações relevantes de dados de alta
dimensĂŁo, como Ă© o caso dos dados de conectividade funcional. Esses modelos utilizam os dados obtidos
da rs-fMRI para melhorar as previsões de diagnóstico em relação às técnicas usadas atualmente em
termos de precisão e rapidez, bem como para compreender melhor os padrões patológicos nas conexões
funcionais destes distúrbios, podendo levar à descoberta de novos biomarcadores. Apesar do notável
desempenho destes modelos, a arquitetura natural em caixa-preta dos algoritmos de DL, torna difĂcil
saber quais as informações dos dados de entrada que levaram o modelo a executar uma determinada
previsão, podendo este utilizar informações erradas dos dados para alcançar uma dada inferência,
restringindo o seu uso em ambientes clĂnicos.
O objetivo desta dissertação, desenvolvida no Instituto de BiofĂsica e Engenharia BiomĂ©dica, Ă©
explorar o poder dos modelos DL, de forma a avaliar até que ponto matrizes de conectividade funcional
criadas a partir de diferentes mĂ©tricas estatĂsticas podem fornecer mais informações sobre a
conectividade funcional do cérebro, para além das métricas de correlação convencionalmente usadas
neste tipo de estudos. Foram estudados dois conjuntos de dados bastante utilizados em estudos de
NeurociĂŞncia e que estĂŁo disponĂveis publicamente: o conjunto de dados ABIDE-I, composto por
indivĂduos saudáveis e indivĂduos com doenças do espectro do autismo (ASD), e o conjunto de dados
ADHD-200, com controlos tipicamente desenvolvidos e indivĂduos com transtorno do dĂ©fice de atenção
e hiperatividade (ADHD).
Numa primeira fase foi realizada a computação das matrizes de conetividade funcional de ambos os
conjuntos de dados, usando as diferentes mĂ©tricas estatĂsticas. Para isso, foi desenvolvido cĂłdigo de
MATLAB, onde se utilizam as séries temporais dos sinais BOLD obtidas dos dois conjuntos de dados
para criar essas mesmas matrizes de conectividade funcional, incorporando funções de diferentes
mĂ©tricas estatĂsticas da caixa de ferramentas MULAN, compreendendo o coeficiente de correlação, o
coeficiente de correlação não linear, a informação mútua, a coerência e a entropia de transferência. De
seguida, a classificação dos dados de conectividade funcional, de forma a avaliar o efeito do uso de
diferentes mĂ©tricas estatĂsticas para a criação de matrizes de conectividade funcional na discriminação
de sujeitos saudáveis e patológicos, foi realizada usando dois modelos de DL. O modelo
ConnectomeCNN melhorado e o modelo inovador ConnectomeCNN-Autoencoder foram desenvolvidos
com recurso Ă biblioteca de Redes Neuronais Keras, juntamente com o seu backend Tensorflow, ambos
em Python. Estes modelos, desenvolvidos previamente no Instituto de BiofĂsica e Engenharia
Biomédica, tiveram de ser otimizados de forma a obter a melhor performance, onde vários parâmetros
dos modelos e do respetivo treino dos mesmos foram testados para os dados a estudar. Pretendeu-se
também estudar o efeito de uma abordagem multi-métrica nas tarefas de classificação dos sujeitos de
ambos os conjuntos de dados, sendo que, para estudar essa abordagem as diferentes matrizes calculadas
a partir das diferentes mĂ©tricas estatĂsticas utilizadas, foram combinadas, sendo usados os mesmos
modelos que foram aplicados Ă s matrizes de conectividade funcional de cada mĂ©trica estatĂstica
individualmente. É importante realçar que na abordagem multi-métrica também foi realizada a
otimização dos parâmetros dos modelos utilizados e do respetivo treino, de modo a conseguir a melhor
performance dos mesmos para estes dados. Para além destes dois objetivos, estudou-se o uso de técnicas
de Inteligência Artificial Explicável (XAI), mais especificamente o método Layer-wise Relevance
Propagation (LRP), com vista a superar o problema da caixa-preta dos modelos de DL, com a finalidade
de explicar como Ă© que os modelos estĂŁo a utilizar os dados de entrada para realizar uma dada previsĂŁo.
O método LRP foi aplicado aos dois modelos utilizados anteriormente, usando como dados de entrada
o conjunto de dados ADHD-200, permitindo assim revelar quais as regiões cerebrais mais importantes
no que toca a um diagnĂłstico relacionado com o ADHD.
Os resultados obtidos mostram que o uso de outras mĂ©tricas estatĂsticas para criar as matrizes de
Conectividade Funcional podem ser um complemento bastante Ăştil Ă s mĂ©tricas estatĂsticas
tradicionalmente utilizadas para a classificação entre indivĂduos saudáveis e indivĂduos como ASD e
ADHD. Nomeadamente mĂ©tricas estatĂsticas nĂŁo lineares como o h2 e a informação mĂştua, obtiveram
desempenhos semelhantes e, em alguns casos, desempenhos ligeiramente melhores em relação aos
desempenhos obtidos por métodos de correlação, convencionalmente usados nestes estudos de
conectividade funcional. A utilização da multi-métrica de conectividade funcional, apesar de não
apresentar melhorias no desempenho geral da classificação em relação ao melhor método das matrizes
de conectividade funcional individuais do conjunto de mĂ©tricas estatĂsticas abordadas, apresenta
resultados que justificam a exploração mais aprofundada deste tipo de abordagem, de forma a
compreender melhor a complementaridade das métricas e a melhor maneira de as utilizar. O uso do
método LRP aplicado ao conjunto de dados do ADHD-200 mostrou a sua aplicabilidade a este tipo de
estudos e a modelos de DL, identificando as regiões cerebrais mais relacionadas à fisiopatologia do
diagnĂłstico do ADHD que sĂŁo compatĂveis com o que Ă© reportado por diversos estudos de conectividade
funcional e estudos de alterações estruturais associados a esta doença. O facto destas técnicas de XAI
demonstrarem como é que os modelos de DL estão a usar os dados de entrada para efetuar as previsões,
pode significar uma mais rápida e aceite adoção destes algoritmos em ambientes clĂnicos. Estas tĂ©cnicas
podem auxiliar o diagnóstico e prognóstico destes distúrbios neurológicos e neuropsiquiátricos, que são
na maioria das vezes difĂceis de diferenciar, permitindo aos mĂ©dicos adquirirem um conhecimento em
relação à previsão realizada e poder explicar a mesma aos seus pacientes
Development of Advanced, Clinically Feasible Neuroimaging Methodology with Diffusional Kurtosis Imaging
Diffusion MRI (dMRI) is a powerful, non-invasive tool for probing the structural organization of the human brain. Quantitative dMRI analyses provide unique capabilities for the characterization of tissue microstructure as well as imaging contrast that is not available to other modalities. White matter tractography relies on dMRI and is currently the only non-invasive technique for mapping structural connections in the human brain. In this chapter, we will describe diffusional kurtosis imaging, an effective and versatile dMRI technique, and discuss a clinical problem in temporal lobe epilepsy (TLE) which is insurmountable with current diagnostic approaches. Subsequent chapters will further develop the capabilities of DKI and demonstrate how it may be particularly well suited to overcome current barriers to care in the clinical management of TLE
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