31 research outputs found

    Automatic detection of the carotid artery boundary on cross-sectional MR image sequences using a circle model guided dynamic programming

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    Systematic aerobe training has positive effects on the compliance of dedicated arterial walls. The adaptations of the arterial structure and function are associated with the blood flow-induced changes of the wall shear stress which induced vascular remodelling via nitric oxide delivered from the endothelial cell. In order to assess functional changes of the common carotid artery over time in these processes, a precise measurement technique is necessary. Before this study, a reliable, precise, and quick method to perform this work is not present

    Carotid Artery Segmentation in Ultrasound Images and Measurement of Intima-Media Thickness

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    Constrained snake vs. conventional snake for carotid ultrasound automated IMT measurements on multi-center data sets

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    Accurate intima-media thickness (IMT) measurement of the carotid artery from minimal plaque ultrasound images is a relevant clinical need, since IMT increase is related to the progression of atherosclerosis. In this paper, we describe a novel dual snake-based model for the high-performance carotid IMT measurement, called Carotid Measurement Using Dual Snakes (CMUDS). Snakes (which are deformable contours) adapt to the lumen-intima (LI) and media-adventitia (MA) interfaces, thus enabling the IMT computation as distance between the LI and MA snakes. However, traditional snakes might be unable to maintain a correct distance and in some spatial location along the artery, it might even collapse between them or diverge. The technical improvement of this work is the definition of a dual snake-based constrained system, which prevents the LI and MA snakes from collapsing or bleeding, thus optimizing the IMT estimation. The CMUDS system consists of two parametric models automatically initialized using the far adventitia border which we automatically traced by using a previously developed multi-resolution approach. The dual snakes evolve simultaneously and are constrained by the distances between them, ensuring the regularization of LI/MA topology. We benchmarked our automated CMUDS with the previous conventional semi-automated snake system called Carotid Measurement Using Single Snake (CMUSS). Two independent readers manually traced the LIMA boundaries of a multi-institutional, multi-ethnic, and multi-scanner database of 665 CCA longitudinal 2D images. We evaluated our system performance by comparing it with the gold standard as traced by clinical readers. CMUDS and CMUSS correctly processed 100% of the 665 images. Comparing the performance with respect to the two readers, our automatically measured IMT was on average very close to that of the two readers (IMT measurement biases for CMUSS was equal to −0.011 ± 0.329 mm and −0.045 ± 0.317 mm, respectively, while for CMUDS, it was 0.030 ± 0.284 mm and −0.004 ± 0.273 mm, respectively). The Figure-of-Merit of the system was 98.5% and 94.4% for CMUSS, while 96.0% and 99.6% for CMUDS, respectively. Results showed that the dual-snake system CMUDS reduced the IMT measurement error accuracy (Wilcoxon, p < 0.02) and the IMT error variability (Fisher, p < 3 × 10−2). We propose the CMUDS technique for use in large multi-centric studies, where the need for a standard, accurate, and automated IMT measurement technique is require

    Automating Carotid Intima-Media Thickness Video Interpretation with Convolutional Neural Networks

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    Cardiovascular disease (CVD) is the leading cause of mortality yet largely preventable, but the key to prevention is to identify at-risk individuals before adverse events. For predicting individual CVD risk, carotid intima-media thickness (CIMT), a noninvasive ultrasound method, has proven to be valuable, offering several advantages over CT coronary artery calcium score. However, each CIMT examination includes several ultrasound videos, and interpreting each of these CIMT videos involves three operations: (1) select three end-diastolic ultrasound frames (EUF) in the video, (2) localize a region of interest (ROI) in each selected frame, and (3) trace the lumen-intima interface and the media-adventitia interface in each ROI to measure CIMT. These operations are tedious, laborious, and time consuming, a serious limitation that hinders the widespread utilization of CIMT in clinical practice. To overcome this limitation, this paper presents a new system to automate CIMT video interpretation. Our extensive experiments demonstrate that the suggested system significantly outperforms the state-of-the-art methods. The superior performance is attributable to our unified framework based on convolutional neural networks (CNNs) coupled with our informative image representation and effective post-processing of the CNN outputs, which are uniquely designed for each of the above three operations.Comment: J. Y. Shin, N. Tajbakhsh, R. T. Hurst, C. B. Kendall, and J. Liang. Automating carotid intima-media thickness video interpretation with convolutional neural networks. CVPR 2016, pp 2526-2535; N. Tajbakhsh, J. Y. Shin, R. T. Hurst, C. B. Kendall, and J. Liang. Automatic interpretation of CIMT videos using convolutional neural networks. Deep Learning for Medical Image Analysis, Academic Press, 201

    Fully automated segmentation and tracking of the intima media thickness in ultrasound video sequences of the common carotid artery

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    Abstract—The robust identification and measurement of the intima media thickness (IMT) has a high clinical relevance because it represents one of the most precise predictors used in the assessment of potential future cardiovascular events. To facilitate the analysis of arterial wall thickening in serial clinical investigations, in this paper we have developed a novel fully automatic algorithm for the segmentation, measurement, and tracking of the intima media complex (IMC) in B-mode ultrasound video sequences. The proposed algorithm entails a two-stage image analysis process that initially addresses the segmentation of the IMC in the first frame of the ultrasound video sequence using a model-based approach; in the second step, a novel customized tracking procedure is applied to robustly detect the IMC in the subsequent frames. For the video tracking procedure, we introduce a spatially coherent algorithm called adaptive normalized correlation that prevents the tracking process from converging to wrong arterial interfaces. This represents the main contribution of this paper and was developed to deal with inconsistencies in the appearance of the IMC over the cardiac cycle. The quantitative evaluation has been carried out on 40 ultrasound video sequences of the common carotid artery (CCA) by comparing the results returned by the developed algorithm with respect to ground truth data that has been manually annotated by clinical experts. The measured IMTmean ± standard deviation recorded by the proposed algorithm is 0.60 mm ± 0.10, with a mean coefficient of variation (CV) of 2.05%, whereas the corresponding result obtained for the manually annotated ground truth data is 0.60 mm ± 0.11 with a mean CV equal to 5.60%. The numerical results reported in this paper indicate that the proposed algorithm is able to correctly segment and track the IMC in ultrasound CCA video sequences, and we were encouraged by the stability of our technique when applied to data captured under different imaging conditions. Future clinical studies will focus on the evaluation of patients that are affected by advanced cardiovascular conditions such as focal thickening and arterial plaques

    The Segmentation of Ultrasound Images for Artery Wall Detection and Intima-Media Thickness Measurement

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    Tato práce je zaměřena na problematiku měření šířky vrstev intima a media (intima media thickness), která se z medicínského pohledu ukazuje jako vhodná pro ohodnocení rizik plynoucích z různých onemocnění kardiovaskulárního systému. Šířka intima media je měřena v ultrazvukovém obraze, který zobrazuje arterii carotis communis v jejím podélném řezu, ve kterém jsou patrné měřené vrstvy intima a media. Práce zahrnuje teoretickou analýzu problematiky z technického i medicínského pohledu a shrnuje současný stav zkoumané problematiky. V práci je popsán návrh nového plně automatického systému pro měření šířky vrstev intima media. Navržený systém zahrnuje i robustní proceduru lokalizace arterie a je tak schopen bez počáteční inicializace či úpravy vstupních dat zpracovávat přímo zdrojová data získaná ultrazvukovou stanicí v B-módu.The thesis focuses on the measurement of intima media thickness, which seems to be a significant marker of the risk of cardiovascular events. Intima media thickness is measured in ultrasound image displaying the common carotid artery in its longitudinal section. In the longitudinal section the intima and media layers are visible. Thesis is discussing both technical and medical background and summarizes state of the art in this field. The main part of the thesis describes the novel automatic system for measurement of intima media thickness. Proposed system includes also robust method for artery localization and therefore is able to process raw B-mode data from ultrasound station without any initialization or manual preprocessing.

    Cyclic variation of the common carotid artery structure in relation to prior atherosclerotic burden and physical activity

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    Background and aims: Cardiovascular disease (CVD) accounts for the most deaths of non-communicable diseases worldwide. It begins with structural and functional changes of the arterial system commonly known as the atherosclerotic process, starting asymptomatically in early childhood, adapting arterial structure and function with advancing age depending on genetic and environmental exposures and finally resulting in CVD events such as myocardial infarction or stroke. CVD risk prediction today is generally based on risk scores, but substantial disadvantages occur since they account only for specific risk factors at one time point. Carotid structure and function (also called carotid stiffness) parameters measured by ultrasound may overcome this disadvantage, since they can provide information on structural and elastic carotid properties and reflect therefore vascular damage accumulated over time. Thus, the aims of this thesis were to summarize the state of the art of ultrasound measurements, to validate the new developed ultrasound analysis system, to assess the variability and reproducibility within the study sample and to investigate the long- and short-term associations of cardiovascular risk factors and carotid stiffness with main focus on physical activity in elderly participants of the SAPALDIA cohort. Methods: The SAPALDIA cohort study is an ongoing multicenter study with a population-based random sample of adults from eight rural and urban areas started in 1991 (SAPALDIA 1), with a first follow-up in 2001-2003 (SAPALDIA 2) and a second follow-up in 2010-2011 (SAPALDIA 3). In SAPALDIA 3, sequential B-mode ultrasound images of the common carotid artery were examined in 3489 participants (51% women) aged between 50-81 years at the time of examination. Expert readers analyzed these ultrasound images with a new analysis system called DYARA (DYnamic ARtery Analysis) according to the state of the art assessed in the review. Thereof, carotid structure parameters were measured and carotid stiffness indices were derived considering blood pressure at time of ultrasound assessment. Validation of the ultrasound analysis program DYARA and reproducibility of carotid parameters were performed in subgroup within the SAPALDIA 3 survey. The presented studies within this thesis comprise cardiovascular risk factor data from the first and second follow-up and therefore, long- and short-term associations with carotid stiffness could be investigated. Results: The intra- and inter-reader results of the validation study were highly consistent with slightly higher bias for analyses with manual interactions compared to the automatic detection. Among the carotid structure parameters, average values across heart cycle showed lower variability than single images in diastole and systole, whereby the relative difference was smaller in lumen diameter values compared to the carotid intima media thickness (CIMT). Based on different statistical approaches, reproducibility values within SAPALDIA 3 were consistently good to excellent for carotid structure and function indices. Findings additionally revealed that subjects itself were the greatest source of variability between two measurements. Multivariate regression analyses suggested that most single cardiovascular risk factors in SAPALDIA 2 were long-termly associated with increased carotid stiffness in SAPALDIA 3 except physical activity and high-density lipoprotein cholesterol (HDL-C). HDL-C was the only protective vascular determinant and no relation was observed for physical activity. Most carotid stiffness parameters were similar strong associated within each cardiovascular risk factor (except compliance showed main deviances among several risk factors). Estimating sex-specific associations of atherosclerotic risk factors and carotid stiffness indicated that increased heart rate was more strongly associated with stiffer arteries across all carotid stiffness parameters in men than in women. Low-density lipoprotein cholesterol (LDL-C) was significantly associated with carotid stiffness only in men and triglyceride only in women. Multifactorial pathway analyses of cardiovascular risk factors in SAPALDIA 3 showed that age was the strongest predictor of carotid stiffness, followed by mean arterial blood pressure and heart rate. Age strongly confounded the association of physical activity and carotid stiffness in multiple regression analyses and therefore, only an univariate association of physical activity and carotid stiffness could be observed. Conclusion: DYARA tackles the challenge of being able to analyze varying ultrasound image qualities with high precision. The high reproducibility and the feasible application in a large sample size suggest that this program can be recommended for epidemiological research, diagnostics and clinical practice. Long- and short-term cardiovascular exposures have added important information to the overall vascular damage assessed by carotid stiffness for both sexes. Although age was the strongest predictor, sex-differences in long-term associations may indicate a certain differentiated susceptibility to cardiovascular risk factors among men and women, which should be investigated in more detail. The presented studies within this thesis provide an important basis towards future investigations targeting the early and late consequences of atherosclerosis, its progression and possible implementations of preventive and/or personalized interventions

    Ultrasound Guidance in Perioperative Care

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    Ultrasound Guidance in Perioperative Care

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    Desarrollo de técnicas específicas de procesado de imagen para su aplicación a la medida del grosor íntima-media de la arteria carótida sobre imágenes de ultrasonidos

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    [ESP] Las enfermedades cardiovasculares son una de las principales causas de mortalidad del mundo. Tras la mayoría de muertes por enfermedad cardiovascular la principal responsable es la arteriosclerosis. La arteriosclerosis consiste en un engrosamiento progresivo del tejido vascular que reduce la elasticidad de los vasos sanguíneos afectados y puede llegar incluso a obstruirlos. Esta enfermedad se desarrolla en la infancia y adolescencia, pudiendo llegar a pasar desapercibida toda la vida o bien actuando como detonador de otras afecciones más serias, como infartos, derrames cerebrales o isquemias. Por todo ello, la detección precoz de la arteriosclerosis resulta de vital importancia. En la actualidad, se viene usando el grosor íntima-media o IMT de la arteria carótida común como indicador fiable y precoz de la arteriosclerosis. Este indicador mide el grosor entre las capas íntima y media de la carótida común en cortes longitudinales de la arteria en imágenes ecográficas. El uso de los ultrasonidos para extraer esta medida, además de barato, resulta no invasivo para el paciente. Sin embargo, esta modalidad de imagen no está exenta de desventajas, como el elevado nivel de ruido que presenta o la alta dependencia del operador. La medida del IMT se realiza de manera manual sobre imágenes de ultrasonidos. Para ello, un observador experto realiza de una a cinco mediciones manuales del grosor de la arteria, donde cada medición consiste en un par de puntos. La presente Tesis Doctoral pretende realizar una segmentación automática de las paredes de la arteria carótida común, de modo que, en lugar de un conjunto de puntos limitado, se pueda extraer el IMT en toda la longitud de la arteria presente en la ecografía. De forma adicional al IMT, se segmenta también la pared anterior de la arteria, pudiendo así proporcionar no sólo el grosor del vaso, sino también el diámetro del cauce de la arteria. El hecho de que sea una segmentación totalmente automática, evita la interacción con el usuario existente en otros métodos de ayuda a la medida del IMT, a la vez que elimina la subjetividad de la medida. Para llevar a cabo una delineación automática de las paredes arteriales, el método desarrollado se implementa en dos etapas básicas. La primera consiste en la detección automática del lumen o cauce por el que fluye la sangre. En una segunda etapa, tras la detección del lumen, se refina el resultado mediante el uso de contornos activos o snakes. En esta Tesis, se emplean contornos activos implementados en el dominio frecuencial. Esta implementación consigue una importante reducción en el coste computacional respecto a la formulación original. Como función de forma se emplean B-splines cúbicas, que presentan una excelente relación entre rendimiento y tiempo de ejecución. El uso de splines proporciona unos contornos finales suaves, lo que evita la típica rugosidad presente en las imágenes de ultrasonidos. Los resultados tras el algoritmo de contornos activos se validan automáticamente para evitar la inclusión de tramos erróneos en las medidas finales. Estos tramos erróneos están ocasionados, principalmente, por la presencia de huecos en la imagen que dificultan el proceso de segmentación, por no proporcionar ninguna información a la imagen de fuerzas externas. Esta validación de los resultados se basa en dos estrategias: estadística y de intensidad. Combinando ambas estrategias se descartan tramos en los que no haya información o en los que la medida resulte anatómicamente improbable. Se ha llevado a cabo una caracterización de los resultados extensa, empleando cuatro métricas distintas para la evaluación de las distancias entre contornos. Tomando el promedio de cuatro segmentaciones manuales como ground truth, se ha comparado con la segmentación automática calculada por el algoritmo de snakes. Tanto las medidas de IMT y del diámetro del lumen, como las distancias entre trazados manuales y automáticos se han evaluado para las cuatro métricas consideradas. En cada caso, se ha calculado el coeficiente de correlación de Pearson, la distribución del error, así como los diagramas de Bland-Altman. A diferencia de otros métodos, en los que la resolución espacial es la misma para todas las imágenes, la configuración del ecógrafo se ha dejado a criterio de los radiólogos. De esta manera, la resolución espacial varía de una imagen a otra, situándose en un rango de 0,029 mm/píxel a 0,082 mm/píxel. Para las 58 imágenes analizadas, se ha logrado medir el IMT en todas ellas. El error medio midiendo el IMT es comparable e incluso inferior al de otros métodos automáticos. El error de segmentación o la distancia directa entre trazados manuales y automáticos es muy bajo, siendo como máximo de unos 2 píxeles para cualquiera de los tres contornos delineados. Como ayuda a la transferencia de resultados, se ha implementado una interfaz de usuario instalable en cualquier PC que implementa el método desarrollado. Esto facilita su uso por parte de personal médico interesado en evaluar el riesgo cardiovascular, tanto de pacientes concretos como de un conjunto de personas para su posterior análisis. Así pues, el método aquí descrito es útil tanto en la práctica clínica diaria como para la realización de estudios del riesgo cardiovascular en la población general. [ENG] Cardiovascular diseases (CVDs) are one of the main causes of death worldwide. Amongst all deaths related to CVDs, atherosclerosis is responsible for the biggest amount of them. Atherosclerosis consists in a progressive thickening of vascular tissue, provoking a loss of elasticity and an increase of thickness of the blood vessels. This thickening can even occlude the affected vessels. This pathology, which is developed during childhood and adolescence, may be unnoticed for years before triggering other more serious conditions, such as infarction, stroke or ischemia. For these reasons, an early detection of atherosclerosis is of paramount interest. Nowadays, the intima-media thickness (IMT) of the common carotid artery is being used as a reliable and early atherosclerosis detector. IMT measures the thickness between intima and media layers of the common carotid artery in longitudinal cuts of the artery in ultrasound images. The use of ultrasound imaging is relatively cheap as well as being non invasive for the patient. However, this image modality presents some drawbacks as it is operator dependent and is quite affected by noise. IMT is manually measured on ultrasound images. With that purpose, an expert observer takes from one to five measurements of the artery thickness. Each manual measurement consists in placing a pair of markers on the artery wall. The present PhD thesis aims at automatically segmenting the layers of the common carotid artery. Thus, instead of a limited set of points, IMT can be measured along the artery length. In addition to IMT, near wall of the artery is also segmented, which provides not only the artery wall thickness, but also the diameter of the artery channel. The fact that the segmentation is completely automatic avoids the user interaction which is present in other IMT measurent methods and, thus, removes the subjetivity of the measurement. To automatically delineate the artery walls, the developed method is implemented in two main stages. The first of them comprises the automatic detection of the lumen, which is the channel where the blood flows. During the second stage, after the lumen detection, the result is refined by means of active contours or snakes. Automatic lumen detection is performed thanks to a correlation of the ultrasound image with a model of the intima-media complex. This step allows the detection of the far wall, which is placed at the bottom of the lumen. In this stage a median filtering is also used to reduce the characteristic speckle noise in ultrasound images. The median filtering gives an image with homogeneous regions, while maintaining the edges of the vessel. Therefore, the median filtering helps in the robustness of the method when there are blood turbulences or backscattering. From the edges of the lumen, active contours or snakes are initialized. The snakes refine the result of the previous stage and provide the different interfaces that define IMT and lumen diameter. Three curves are considered, one for the near wall (located above the lumen in the ultrasound image) and two for the far wall (located under the lumen in the ultrasound image), corresponding to the lumen-intima and media-adventitia interface that determine IMT. In the present work, a Fourier-domain implementation of active contours is used. This implementation achieves a considerable computational cost reduction with respect to the original formulation. Cubic B-splines have been chosen as shape function because of their excellent performance versus running time ratio. Moreover, B-splines provide soft final contours, dealing with the typical rugosity in ultrasound images. Besides the frequency implementation of snakes, the success of the refinement stage is based on the calculation of an adequate external forces image. To compute the external forces image, positive and negative transitions of the intensity gradient of the image are combined in a single image. This combination allows the simultaneous convergence of the near and far wall curves. Although the external force image contains plenty information of the edges to be detected, combined gradient image might not be clear enough. Hence, a morphological reconstruction is performed, being the mask image the combined gradient image. As marker, the cumulative result of morphological openings is used. The openings are performed over the combined gradient image, being the structuring elements lines oriented in the main directions of the gradient image. These main directions are extracted via a Hough transform. Finally, the reconstruction result gives a clearer edge image, in which small structures disappear, making the convergence of the snakes faster. The results after the active contour algorithm are automatically validated to avoid the inclusion of wrong segmented sections in the final measurements. These wrong sections are due to, mainly, the presence of gaps in the image which do not provide any information about the external forces image. This additional validation stage is based on two strategies, statistical and intensity-based. By combining both strategies, we avoid the inclusion of sections with big gaps or in which the measurements are unlikely in anatomical terms. An exhaustive result characterization has been accomplished. Four different metrics have been used to evaluate the distances between contours. Considering the average of four manual measurements as ground truth, automatic segmentation has been compared to manual segmentation. The four considered metrics have been used to evaluate the IMT, the lumen diameter and the distances between manual and automatic delineations. En each case, Pearson’s correlation coefficient, error distribution and Bland-Altman’s plots have been calculated. The ultrasound image dataset has been obtained with a single ultrasound scanner with two different probes, each of them working at different frequency range. Unlike other methods, in which the spatial resolution is not variable, the scanner configuration is flexible for the radiologist, at his/her own discretion. Thus, spatial resolution may vary from one image to another, ranging from 0.029 mm/pixel to 0.082 mm/pixel in our database. IMT has been automatically measured in all 58 images in our database. The images correspond to 35 patients, none of them previously diagnosed with atherosclerosis. The mean IMT error is comparable or even less than the error in other automatic methods. Besides, the distance between manual and automatic contours is very low, being under 2 pixels for any of the three detected interfaces. In order to disseminate and transfer the results, a user interface has been implemented. The program can be installed in any PC, which makes its use easier. Medical staff interested in the evaluation of cardiovascular risk cannot only use the interface for individual patients but also for population-based studies. Thus, the developed method is useful in daily clinical practice as well as in cardiovascular risk studies over population. The segmentation of the carotid artery layers allows the calculation of other measurements and statistics apart from the mean IMT. Maximum and minimum values, texture or ecogenicity in the intimamedia complex region can be extracted. In a similar way, it is possible to monitor the atherosclerosis evolution via registration methods. Therefore, the doctor could easily detect slight changes in the IMT and adjust the treatment and recommendations to the patient in a reliable way. Besides, since the developed technique is based on snakes, the method is easily extendable to 3D cases. This would lead to new applications of the segmentation, such as the analysis of the IMT during a whole systole and diastole cycle or the study of the elastogram of the carotid artery.Universidad Politécnica de Cartagen
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