From 4D medical images (CT, MRI, and Ultrasound) to 4D structured mesh models of the left ventricular endocardium for patient-specific simulations

With cardiovascular disease (CVD) remaining the primary cause of death worldwide, early detection of CVDs becomes essential. The intracardiac flow is an important component of ventricular function, motion kinetics, wash-out of ventricular chambers, and ventricular energetics. Coupling between Computational Fluid Dynamics (CFD) simulations and medical images can play a fundamental role in terms of patient-specific diagnostic tools. From a technical perspective, CFD simulations with moving boundaries could easily lead to negative volumes errors and the sudden failure of the simulation. The generation of high-quality 4D meshes (3D in space + time) with 1-to-l vertex becomes essential to perform a CFD simulation with moving boundaries. In this context, we developed a semiautomatic morphing tool able to create 4D high-quality structured meshes starting from a segmented 4D dataset. To prove the versatility and efficiency, the method was tested on three different 4D datasets (Ultrasound, MRI, and CT) by evaluating the quality and accuracy of the resulting 4D meshes. Furthermore, an estimation of some physiological quantities is accomplished for the 4D CT reconstruction. Future research will aim at extending the region of interest, further automation of the meshing algorithm, and generating structured hexahedral mesh models both for the blood and myocardial volume

Algorithm for defining skeletal structures in biomedical models

La descripción del comportamiento mecánico de tejidos duros mediante el empleo de modelos discretos pasa por diferentes etapas de análisis, desde el procesamiento digital de la imagen hasta la especificación de las propiedades físicas del tejido. Para ello, es necesario tener en cuenta un elemento clave: la descomposición del modelo en sus partes constitutivas. Se realizó un estudio bibliográfico de diversas propuestas para realizar la descomposición y se llegó a la conclusión de la inexistencia de una estrategia única. Existe un cúmulo de propuestas genéricas, pero estas no ofrecen una solución válida a los casos analizados, correspondientes a las articulaciones de la rodilla, la pelvis y el hombro. Por tanto, se propone un algoritmo para realizar la descomposición mediante el análisis de las relaciones espaciales entre los contornos presentes en planos consecutivos, que se basa en 4 etapas: la lectura de los cortes de imágenes de tomografía computarizada; la determinación de los contornos que definen el tejido óseo presente en cada corte; el agrupamiento de los contornos cuya relación espacial cumple un criterio determinado, y la eliminación de los volúmenes no válidos. Los resultados del algoritmo se compararon con otros obtenidos mediante el empleo de la librería Visualization ToolKit (VTK) y pyFormex, cuyos métodos se utilizan en la visualización y análisis de imágenes médicas y en la modelación de estructuras tridimensionales. Como resultado del algoritmo propuesto tenemos —bajo las mismas condiciones y en un corto tiempo de procesamiento— una descomposición de los modelos anatómicos superior a la realizada por VTK y pyFormex, con aproximadamente el 90% de confianza.Description of mechanical behavior of hard tissues by means of discrete models goes through various stages of analysis, which range from digital image processing to the specification of physical properties of tissue to the discrete model. This requires taking into account a key element: the decomposition of the model into its constituent parts. We conducted a bibliographic study of existing proposals for such decomposition, leading to the conclusion of the absence of a single strategy. There are several generic proposals, but these proved not to give a valid solution applicable to the cases examined corresponding to the articulations of the knee, hip and shoulder. In this paper we propose an algorithm to perform this decomposition by analyzing the spatial relationships between the contours present in consecutive planes. It is based on four stages: reading computer tomography (CT) slices; determining the contours that define bone tissue present on each slice; grouping of contours whose relationship meets a given criterion; and eliminating non-valid volumes. Results were compared with those obtained by means of Visualization ToolKit (VTK) and pyFormex, widely used in the visualization and analysis of medical imaging and modeling three-dimensional structures. As a main result, proposed algorithm under the same conditions and short processing time performs a better decomposition of anatomical models than the one made by VTK and pyFormex, with about a 90% of confidence.Peer Reviewe

Obtaining foot bone structure applying global and adaptive thresholding

La descripción del comportamiento mecánico de tejidos duros mediante el empleo de modelos discretos pasa por diferentes etapas de análisis, que van desde el procesamiento digital de la imagen hasta la especificación de las propiedades físicas del tejido al modelo discreto. Para lograr un buen resultado es esencial la descomposición de esos modelos en sus partes constitutivas. En este trabajo se discute un método para la descripción geométrica de los huesos del pie a partir de una secuencia de imágenes (cortes) de tomografía computarizada (TC). La investigación propone la combinación de la umbralización global y de la adaptativa para la determinación del dominio geométrico de los huesos en cada corte, así como el análisis de las relaciones espaciales entre contornos en planos consecutivos a fin de obtener las isosuperficies de los huesos. Se propone un algoritmo semiautomático basado en 4 etapas: la lectura de los cortes de imágenes de TC; la determinación de los contornos que definen el tejido óseo presentes en cada corte; la formación de los volúmenes a través del agrupamiento de los contornos cuya relación espacial cumple un criterio determinado; y la eliminación de las isosuperficies no válidas. Como resultado se obtiene la definición de la mayoría de los huesos del pie cuyo rango de valores en la escala de Hounsfield es [–1.000; 1.383].The description of the mechanical behavior of hard tissues by means of discrete models goes through various stages of analysis, which range from digital image processing to the specification of tissues physical properties to the discrete model. To achieve good results it is essential to decompose these models into their constituent parts. In this paper we discuss a method for geometrical description of foot bones from a sequence of computed tomography (CT) images. This research proposes a combination between global and adaptive thresholdings to determine the geometric domain of bones in each slice and the analysis of the spatial relationships between contours in consecutive planes in order to obtain bones’ isosurfaces. The algorithm proposed is based on 4 stages: the reading of computed tomography (CT) images; the determination of the contours that define the bone tissue present on each slice; the grouping of contours whose relationship meet a given criteria; the elimination of non-valid volumes. As a result, it is possible to obtain the geometrical domain of a great number of foot bones whose range in the Hounsfield is [–1000; 1383].Peer Reviewe

Analysis of the coating integrityduring a coronary stent deployment

Las afecciones cardiovasculares constituyen en la actualidad una causa frecuente de muerte. Una de estas afecciones es la ateroesclerosis, la cual provoca la reducción de la luz arterial. En aras de solucionar tal afección se han desarrollado varios tratamientos, ganando terreno la Angioplastia Coronaria Transluminar Percutánea (PTCA) con colocación de estent. En la actualidad muchos de estos dispositivos son recubiertos para aumentar la biocompatibilidad y disminuir los riesgos de reestenosis. Dado la posibilidad de fallas o roturas de los recubrimientos y los riesgos asociados a estas, es de gran importancia el estudio del comportamiento de la unión estentrecubrimiento durante la fase de expansión del estent. En esta investigación se estudia la posible ocurrencia de delaminación del recubrimiento durante la expansión de un estent y la influencia de parámetros como el espesor y el material del mismo. El estudio parte de la obtención de un modelo geométrico de una celda del estent Sirius Carbostent para su posterior procesamiento por el Método de Elementos Finitos. La simulación por tal método, se desarrolló, aplicando restricciones al movimiento de forma tal que la celda modelada simule su comportamiento durante la expansión de un estent. Considerando estos aspectos fue posible evaluar la integridad del recubrimiento. Con los modelos desarrollados se logró predecir la ocurrencia de delaminación durante la expansión del estent y se determinó que al aumentar el espesor del recubrimiento aumenta el riesgo de ocurrencia de la misma. Se obtuvo además una ecuación general que permite determinar el esfuerzo máximo de contacto para celdas en forma de U.The cardiovascular diseases constitute one of the main causes of death worldwide. One of the main diseases is atherosclerosis, which causes narrowing of the arterial lumen. In order to solve this condition, several treatments have been developed, and Percutaneous Transluminal Coronary Angioplasty (PTCA) with the placement of stent have gained relevancy. Many of these devices are currently coated to increase the biocompatibility and to decrease the restenosis risks. The biomechanical studies of the stent-coating interface behavior are necessary given the associated risks to possibility of failures or breakages of the coating during stent deployment. In this study the possible occurrence of coating delamination during stent deployment and the influence of parameters as the thickness and material were studied. The study starts by obtaining a geometric model of a stent unit of the Sirius Carbostent stent for the further processing by the Finite Element Method. The simulation was developed by applying restrictions so that the modeled stent hinge simulates his behavior during stent deployment. Considering these aspects it was possible to evaluation the coating integrity. With this model it was possible to predict the occurrence of delamination during stent deployment and to determine that the delamination risks increases with increasing the coating thickness. Finally, it was obtained a general function that allows to determine the maximal contact stress for a stent hinge with an U shape.Peer Reviewe

Patient-specific image-based computer simulation for theprediction of valve morphology and calcium displacement after TAVI with the Medtronic CoreValve and the Edwards SAPIEN valve

AIMS: Our aim was to validate patient-specific software integrating baseline anatomy and biomechanical properties of both the aortic root and valve for the prediction of valve morphology and aortic leaflet calcium displacement after TAVI. METHODS AND RESULTS: Finite element computer modelling was performed in 39 patients treated with a Medtronic CoreValve System (MCS; n=33) or an Edwards SAPIEN XT (ESV; n=6). Quantitative axial frame morphology at inflow (MCS, ESV) and nadir, coaptation and commissures (MCS) was compared between multislice computed tomography (MSCT) post TAVI and a computer model as well as displacement of the aortic leaflet calcifications, quantified by the distance between the coronary ostium and the closest calcium nodule. Bland-Altman analysis revealed a strong correlation between the observed (MSCT) and predicted frame dimensions, although small differences were detected for, e.g., Dmin at the inflow (mean±SD MSCT vs. MODEL: 21.6±2.4 mm vs. 22.0±2.4 mm; difference±SD: -0.4±1.3 mm, p<0.05) and Dmax (25.6±2.7 mm vs. 26.2±2.7 mm; difference±SD: -0.6±1.0 mm, p<0.01). The observed and predicted calcium displacements were highly correlated for the left and right coronary ostia (R2=0.67 and R2=0.71, respectively p<0.001). CONCLUSIONS: Dedicated software allows accurate prediction of frame morphology and calcium displacement after valve implantation, which may help to improve outcome

An animal-specific FSI model of the abdominal aorta in anesthetized mice

Recent research has revealed that angiotensin II-induced abdominal aortic aneurysm in mice can be related to medial ruptures occurring in the vicinity of abdominal side branches. Nevertheless a thorough understanding of the biomechanics near abdominal side branches in mice is lacking. In the current work we present a mouse-specific fluid-structure interaction (FSI) model of the abdominal aorta in ApoE(-/-) mice that incorporates in vivo stresses. The aortic geometry was based on contrast-enhanced in vivo micro-CT images, while aortic flow boundary conditions and material model parameters were based on in vivo high-frequency ultrasound. Flow waveforms predicted by FSI simulations corresponded better to in vivo measurements than those from CFD simulations. Peak-systolic principal stresses at the inner and outer aortic wall were locally increased caudal to the celiac and left lateral to the celiac and mesenteric arteries. Interestingly, these were also the locations at which a tear in the tunica media had been observed in previous work on angiotensin II-infused mice. Our preliminary results therefore suggest that local biomechanics play an important role in the pathophysiology of branch-related ruptures in angiotensin-II infused mice. More elaborate follow-up research is needed to demonstrate the role of biomechanics and mechanobiology in a longitudinal setting