REDES NEURAIS APLICADAS NA INVESTIGAÇÃO DE AVC POR TOMOGRAFIA COMPUTADORIZADA

This work introduce an algorithm proposal able to automatically identify the occurrence of stroke through computed tomography (CT) images. The methods of segmentation by similarity and mathematical morphology are defined, in addition to the enhancement filters used to modify the histogram of the image, which comprises the input data of a Multi-layer Perceptron neural network responsible for classification. The use of this algorithm for medical diagnosis assistance seeks to speed up the process of detection of the disease, accurately and satisfactorily, once the final response given by the responsible specialist depends on his subjectivity. The work comes up with the development of the algorithm and the analysis of its results, which reaches an accuracy of 98,51% during the classification training using the anisotropic diffusion filter and 91,33% for segmentation using thresholding methods. A comparison between other image processing and artificial intelligence techniques is performed, seeking to obtain the bets response within a new and low cost model.Este trabalho apresenta uma proposta de algoritmo capaz de identificar automaticamente a ocorrência do acidente vascular encefálico (AVC) usando imagens por tomografia computadorizada (TC). São definidos os métodos de segmentação por similaridade e morfologia matemática, além dos filtros de realce utilizados para modificar o histograma da imagem, que compreende os dados de entrada de uma rede neural Perceptron multicamadas, responsável pela classificação. A utilização deste algoritmo para o auxílio ao diagnóstico médico busca agilizar o processo de detecção da doença, de forma precisa e satisfatória, uma vez que a resposta final dada pelo especialista responsável depende de sua subjetividade. O trabalho mostra o desenvolvimento do algoritmo e a análise de seus resultados, que alcança uma acurácia de 98,51% durante o treinamento de classificação utilizando o filtro de difusão anisotrópica e 91,33% para segmentação utilizando métodos de limiarização. Uma comparação entre outras técnicas de processamento de imagem e inteligência artificial é realizada, procurando obter a melhor resposta dentro de um modelo novo e de baixo custo

Automatic CT Angiography Lesion Segmentation Compared to CT Perfusion in Ischemic Stroke Detection: a Feasibility Study

In stroke imaging, CT angiography (CTA) is used for detecting arterial occlusions. These images could also provide information on the extent of ischemia. The study aim was to develop and evaluate a convolutional neural network (CNN)-based algorithm for detecting and segmenting acute ischemic lesions from CTA images of patients with suspected middle cerebral artery stroke. These results were compared to volumes reported by widely used CT perfusion-based RAPID software (IschemaView). A 42-layer-deep CNN was trained on 50 CTA volumes with manually delineated targets. The lower bound for predicted lesion size to reliably discern stroke from false positives was estimated. The severity of false positives and false negatives was reviewed visually to assess the clinical applicability and to further guide the method development. The CNN model corresponded to the manual segmentations with voxel-wise sensitivity 0.54 (95% confidence interval: 0.44-0.63), precision 0.69 (0.60-0.76), and Sorensen-Dice coefficient 0.61 (0.52-0.67). Stroke/nonstroke differentiation accuracy 0.88 (0.81-0.94) was achieved when only considering the predicted lesion size (i.e., regardless of location). By visual estimation, 46% of cases showed some false findings, such as CNN highlighting chronic periventricular white matter changes or beam hardening artifacts, but only in 9% the errors were severe, translating to 0.91 accuracy. The CNN model had a moderately strong correlation to RAPID-reported T-max > 10 s volumes (Pearson's r = 0.76 (0.58-0.86)). The results suggest that detecting anterior circulation ischemic strokes from CTA using a CNN-based algorithm can be feasible when accompanied with physiological knowledge to rule out false positives.Peer reviewe

Ischemic Stroke Thrombus Characterization through Quantitative Magnetic Resonance Imaging

Stroke is a pervasive, devastating disease and remains one of the most challenging conditions to treat. In particular, risk of recurrence is dramatically heightened after a primary stroke and requires urgent preventative therapy to effectively mitigate. However, the appropriate preventative therapy depends on the underlying source of the stroke, known as etiology, which is challenging to determine promptly. Current diagnostic tests for determining etiology underwhelm in both sensitivity and specificity, and in as much as 35% of cases etiology is never determined. In ischemic stroke, the composition of the occluding thrombus, specifically its red blood cell (RBC) content, has been shown to be indicative of etiology but remains largely ignored within clinical practice. Currently, composition can only be quantified through histological analysis, an involved process that can be completed in only the minority of cases where a thrombus has been physically retrieved from the patient during treatment. The goal of this thesis is to develop a quantitative MR imaging method which is capable of non-invasive prediction of ischemic stroke etiology through assessment of thrombus RBC content. To achieve this goal, we employed quantitative MR parameters that are sensitive to both RBC content and oxygenation, R2* and quantitative susceptibility mapping (QSM), as well as fat fraction (FF) mapping, and evaluated the ability of modern artificial intelligence techniques to form predictions of RBC content and etiology based on these quantitative MR parameters alone and in combination with patient clinical data. First, we performed an in vitro blood clot imaging experiment, which sought to explicitly define the relationship between clot RBC content, oxygenation and our quantitative MR parameters. We show that both R2* and QSM are sensitive to RBC content and oxygenation, as expected, and that the relationship between R2* and QSM can be used to predict clot RBC content independent of oxygenation status, a necessary step for stroke thrombus characterization where oxygenation is an unknown quantity. Second, we trained a deep convolutional neural network to predict histological RBC content from ex vivo MR images of ischemic stroke thrombi. We demonstrate that a convolutional neural network is capable of RBC content prediction with 66% accuracy and 8% mean absolute error when trained on a limited thrombus dataset, and that prediction accuracy can be improved to up to 74% through data augmentation. Finally, we used a random forest classifier to predict clinical stroke etiology using the same ex vivo thrombus MR image dataset. Here, quantitative thrombus R2*, QSM and FF image texture features were used to train the classifier, and we demonstrate that this method is capable of accurate etiology prediction from thrombus texture information alone (accuracy = 67%, area under the curve (AUC) = 0.68), but that when combined with patient clinical data the performance of the classifier improves dramatically to an accuracy and AUC of 93% and 0.89, respectively. Together, the works presented in this thesis offer extensive ex vivo evidence that quantitative MR imaging is capable of effective stroke thrombus etiology characterization. Such a technique could enable clinical consideration of thrombus composition and bolster stroke etiology determination, thereby improving the management and care of acute ischemic stroke patients