2022 IEEE 61st Conference on Decision and Control (CDC)
We consider a perimeter defense problem in a planar conical environment in which a single vehicle... more We consider a perimeter defense problem in a planar conical environment in which a single vehicle, having a finite capture radius, aims to defend a concentric perimeter from mobile intruders. The intruders are arbitrarily released at the circumference of the environment and move radially toward the perimeter with fixed speed. We present a competitive analysis approach to this problem by measuring the performance of multiple online algorithms for the vehicle against arbitrary inputs, relative to an optimal offline algorithm that has access to all future inputs. In particular, we first establish a necessary condition on the parameter space to guarantee finite competitiveness of any algorithm, and then characterize a parameter regime in which the competitive ratio is guaranteed to be at least 2 for any algorithm. We then design and analyze three online algorithms and characterize parameter regimes for which they have finite competitive ratios. Specifically, our first two algorithms are provably 1, and 2-competitive, respectively, whereas our third algorithm exhibits a finite competitive ratio that depends on the problem parameters. Finally, we provide numerous parameter space plots providing insights into the relative performance of our algorithms.
A conflict between rational and autonomous agents is considered. The paper addresses a differenti... more A conflict between rational and autonomous agents is considered. The paper addresses a differential game of protecting a target in the 3-D space. This problem highlights the strong correlation between the highly dynamic scenario, the uncertainty on the behavior of the adversary, and the online and robust computation of state-feedback strategies which guarantee the required level of performance of each player. This work significantly expands previous results around this problem by providing the players' state-feedback saddle-point strategies. Additionally, the continuously differentiable Value function of the multi-agent differential game is obtained and it is shown to be the solution of the Hamilton-Jacobi-Isaacs equation. Finally, the Barrier surface is explicitly obtained and illustrative examples highlight the robustness properties and the guarantees provided by the saddle-point strategies obtained in this paper.
In the current investigation, a guided meditation technique was designed to reach the spiritual a... more In the current investigation, a guided meditation technique was designed to reach the spiritual aspect of the inner consciousness in order to receive its influence and by being able to think according to sustainable patterns. During the meditation and through a marketing process, participants selected the best options of products or services which fit their spiritual concerns. In the end, participants discovered ways to do business by taking care of the environment and by being able to feel joy due to the approach they had with their inner spiritual aspect.
Se aspira a clarificar la posición del rey en el sistema constitucional español, descifrando el s... more Se aspira a clarificar la posición del rey en el sistema constitucional español, descifrando el significado de la fórmula «árbitro y moderador» recogida en el art. 56 de la Constitución al amparo de la idea de neutralidad. Para ello, se procede, primero, a ojear la posición del monarca surgido de la transición política a través de sus caracteres constitucionales, y segundo a efectuar un rastreo en los supuestos de la teoría del Estado Constitucional, a fin de establecer las categorías que pudieran ser coherentes con los valores democráticos. En base al fundamento que depara esta categorización se llega a la conclusión de que en el actual momento político español, no cabe otro modelo creíble que el que se corresponde con «la republicana coronada», advirtiendo, al tiempo, que la verdadera clave del problema reside no tanto en la existencia de modelos alternativos cómo y en términos de Locke, en su «reasonablessnes», esto es, en la plausibilidad o credibilidad social que sea capaz de c...
En el presente artículo se plantea una crítica a la tesis que define la Transición política españ... more En el presente artículo se plantea una crítica a la tesis que define la Transición política española como un exitoso intento de poner punto final a la “ley del péndulo” que había venido rigiendo nuestra historia constitucional. Por un lado, esta tesis minusvalora las condiciones de la situación española de 1978, marcada por el tránsito entre dos mundos, el moderno que heredaba y el emergente postmoderno, que se convertiría en una realidad incuestionable a partir de 1989. Además, la Constitución española de 1978 se redactó en un momento en que estaban declinando los supuestos conceptuales político-normativos del paradigma constitucional dominante en Europa tras la Segunda Guerra Mundial
The two-dimensional nature of mammography makes estimation of the overall breast density challeng... more The two-dimensional nature of mammography makes estimation of the overall breast density challenging, and estimation of the true patient-specific radiation dose impossible. Digital breast tomosynthesis (DBT), a pseudo-3D technique, is now commonly used in breast cancer screening and diagnostics. Still, the severely limited 3rd dimension information in DBT has not been used, until now, to estimate the true breast density or the patient-specific dose. In this study, we propose a reconstruction algorithm for DBT based on deep learning specifically optimized for these tasks. The algorithm, which we name DBToR, is based on unrolling a proximal primal-dual optimization method, where the proximal operators are replaced with convolutional neural networks and prior knowledge is included in the model. This extends previous work on a deep learning based reconstruction model by providing both the primal and the dual blocks with breast thickness information, which is available in DBT. Training and testing of the model were performed using virtual patient phantoms from two different sources. Reconstruction performance, as well as accuracy in estimation of breast density and radiation dose, was estimated, showing high accuracy (density < ±3%; dose < ±20%), without bias, significantly improving on the current state-of-the-art. This work also lays the groundwork for developing a deep learning-based reconstruction algorithm for the task of image interpretation by radiologists.
Intensity-based registration algorithms have been widely used in medical image applications. This... more Intensity-based registration algorithms have been widely used in medical image applications. This type of registration algorithms uses an object function to compute a transformation and optimizes a measure of similarity between the images being registered. The most common similarity metrics used in registration are sum of squared differences, mutual information and normalized cross-correlation. This paper aims to compare these similarity metrics, using common registration algorithms applied to breast density maps registration. To evaluate the results, we use the protocols for evaluation of similarity measures proposed byŠkerl et al. They consist in defining a set of random directions in the parameter space of the registration algorithm and compute statistical measures, such as the accuracy, capture range, number of maxima and risk of non-convergence, along these directions. The obtained results show a better performance corresponding to normalized cross-correlation for the rigid registration algorithm, while the sum of squared difference obtains the best result for the B-Spline method.
In this paper an N-pursuer vs. M-evader team conflict is studied. The differential game of border... more In this paper an N-pursuer vs. M-evader team conflict is studied. The differential game of border defense is addressed and we focus on the game of degree in the region of the state space where the pursuers are able to win. This work extends classical differential game theory to simultaneously address weapon assignments and multi-player pursuit-evasion scenarios. Saddle-point strategies that provide guaranteed performance for each team regardless of the actual strategies implemented by the opponent are devised. The players' optimal strategies require the co-design of cooperative optimal assignments and optimal guidance laws. A representative measure of performance is proposed and the Value function of the game is obtained. It is shown that the Value function is continuous, continuously differentiable, and that it satisfies the Hamilton-Jacobi-Isaacs equation-the curse of dimensionality is overcome and the optimal strategies are obtained. The cases of N = M and N > M are considered. In the latter case, cooperative guidance strategies are also developed in order for the pursuers to exploit their numerical advantage. This work provides a foundation to formally analyze complex and high-dimensional conflicts between teams of N pursuers and M evaders by means of differential game theory. This work has been supported in part by AFOSR LRIR No. 18RQCOR036.
Se trata de tomar como hilo conductor la lectura que Manuel García- Pelayo hace del pensamiento d... more Se trata de tomar como hilo conductor la lectura que Manuel García- Pelayo hace del pensamiento de Maquiavelo, para reflexionar acerca de la conveniencia de efectuar una reflexión sobre nuestra vida política desde la Teoría del Estado constitucional. La Teoría del Estado parece ser una categoría prescindible para los actuales estudiosos de la Constitución, cuando los problemas a que asistimos no pueden ser satisfactoriamente explicados acudiendo sólo a las explicaciones que nos dan las normas del Derecho. Por eso se hace necesario considerar lo que ahora están diciendo los autores de Cambridge (Pocock, Dunn, Skinner, Tuck, Pagden) para saber si es posible reconstruir una Teoría del Estado que satisfaga las deficiencias del Derecho Constitucional para abordar una realidad política que parece desbordada por los problemas de la gobernabilidad, el declive de la libertad política o la corrupción
FORO. Revista de Ciencias Jurídicas y Sociales, Nueva Época, 2019
Se elabora una propuesta para incardinar los textos políticos discursivos dentro del mundo del De... more Se elabora una propuesta para incardinar los textos políticos discursivos dentro del mundo del Derecho constitucional, especialmente dentro de su enseñanza.
Breast magnetic resonance imaging (MRI) and X-ray mammography are two image modalities widely use... more Breast magnetic resonance imaging (MRI) and X-ray mammography are two image modalities widely used for early detection and diagnosis of breast diseases in women. The combination of these modalities, traditionally done using intensity-based registration algorithms, leads to a more accurate diagnosis and treatment, due to the capability of co-localizing lesions and susceptibles areas between the two image modalities. In this work, we present the first attempt to register breast MRI and X-ray mammographic images using intensity gradients as the similarity measure. Specifically, a patient-specific biomechanical model of the breast, extracted from the MRI image, is used to mimic the mammographic acquisition. The intensity gradients of the glandular tissue are directly projected from the 3D MRI volume to the 2D mammographic space, and two different gradient-based metrics are tested to lead the registration, the normalized cross-correlation of the scalar gradient values and the gradient correlation of the vectoral gradients. We compare these two approaches to an intensity-based algorithm, where the MRI volume is transformed to a synthetic computed tomography (pseudo-CT) image using the partial volume effect obtained by the glandular tissue segmentation performed by means of an Expectation-Maximization algorithm. This allows us to obtain the digitally reconstructed radiographies by a direct intensity projection. The best results are obtained using the scalar gradient approach along with a transversal isotropic material model, obtaining a target registration error (TRE), in millimeters, of 5.65 ± 2.76 for CC-and of 7.83 ± 3.04 for MLO-mammograms, while the TRE is 7.33 ± 3.62 in the 3D MRI. We also evaluate the effect of the glandularity of the breast as well as the landmark position on the TRE, obtaining moderated correlation values (0.65 and 0.77 respectively), concluding that these aspects need to be considered to increase the accuracy in further approaches.
Medical Imaging 2017: Physics of Medical Imaging, 2017
Scattered radiation is an undesired signal largely present in most digital breast tomosynthesis (... more Scattered radiation is an undesired signal largely present in most digital breast tomosynthesis (DBT) projection images as no physically rejection methods, i.e. anti-scatter grids, are regularly employed, in contrast to fullfield digital mammography. This scatter signal might reduce the visibility of small objects in the image, and potentially affect the detection of small breast lesions. Thus accurate scatter models are needed to minimise the scattered radiation signal via post-processing algorithms. All prior work on scattered radiation estimation has used a rigid breast compression paddle (RP) and reported large contribution of scatter signal from RP in the detector. However, in this work, flexible paddles (FPs) tilting from 0 • to 10 • will be studied using Monte Carlo simulations to analyse if the scatter distribution differs from RP geometries. After reproducing the Hologic Selenia Dimensions geometry (narrow angle) with two (homogeneous and heterogeneous) compressed breast phantoms, results illustrate that the scatter distribution recorded at the detector varies up to 22% between RP and FP geometries (depending on the location), mainly due to the decrease in thickness of the breast observed for FP. However, the relative contribution from the paddle itself (3-12% of the total scatter) remains approximately unchanged for both setups and their magnitude depends on the distance to the breast edge.
Virtual clinical trials (VCT) currently represent key tools for breast imaging optimisation, espe... more Virtual clinical trials (VCT) currently represent key tools for breast imaging optimisation, especially in two-dimensional planar mammography and digital breast tomosynthesis. Voxelised breast models are a crucial part of VCT as they allow the generation of synthetic image projections of breast tissue distribution. Therefore, realistic breast models containing an accurate representation of women breasts are needed. Current voxelised breast models show, in their compressed version, a very round contour which might not be representative of the entire population. This work pretends to develop an imaging framework, based on depth cameras, to investigate breast deformation during mammographic compression. Preliminary results show the feasibility of depth sensors for such task, however post-processing steps are needed to smooth the models. The proposed framework can be used in the future to produce more accurate compressed breast models, which will eventually generate more realistic images in VCT.
2012 IEEE 51st IEEE Conference on Decision and Control (CDC), 2012
A new architecture for model-based control of unstable and uncertain systems with network induced... more A new architecture for model-based control of unstable and uncertain systems with network induced delays, and for set-point tracking over networks, is presented in this paper. This setup provides better performance than similar approaches in terms of steady-state tracking error and reduction of network traffic by transmitting measurement updates only when necessary. The results in this paper also extend previous work using the Model-Based Networked Control Systems (MB-NCS) approach to consider the output feedback case and to consider models and uncertain systems which do not necessarily have the same dimension;; that is, both the parameters and the order of the system are unknown. The Model-Based Event-Triggered (MB-ET) framework presented in this paper is used for stabilization and tracking of piece-wise constant signals and it is extended in two directions;; first, to consider a more general two channel networked system and second, to address the reference input tracking problem in the presence of network induced delays.
Proceedings of the 2011 American Control Conference, 2011
In this paper Model Based Networked Control Systems (MB-NCS) are considered and on-line identific... more In this paper Model Based Networked Control Systems (MB-NCS) are considered and on-line identification of system parameters in state space representation is used to upgrade the model and the controller of the system. The updated model is used to control the real system when feedback information is unavailable. The Extended Kalman Filter (EKF) is analyzed in the context of parameter identification and implemented in the MB-NCS framework. Emphasis is placed on global asymptotic estimators for the case when sensors provide noiseless measurements of the state of a linear system; it can be shown that the identification of parameters in this case is a linear problem, in contrast to the nonlinear combined stateparameter estimation problem. We propose new estimation models that offer better convergence properties than the EKF in this case. This estimation strategy is also applied to the MB-NCS framework resulting in a better usage of the network by allowing longer intervals without need for a measurement update.
Design of optimal controllers for uncertain linear systems subject to communication constraints i... more Design of optimal controllers for uncertain linear systems subject to communication constraints is investigated in this paper. By following the Model-Based Event-Triggered (MB-ET) control framework we are able to design optimal control laws using the nominal models that are robust to model uncertainties and limited communication. For finite horizon optimal control problems we also provide sub-optimal schedulers that estimate the best time instants to send feedback measurements. The nominal optimal controller and sub-optimal scheduler aim at optimizing the performance of the system that considers the control effort as well as the cost of communication both in the presence of model uncertainties.
2022 IEEE 61st Conference on Decision and Control (CDC)
We consider a perimeter defense problem in a planar conical environment in which a single vehicle... more We consider a perimeter defense problem in a planar conical environment in which a single vehicle, having a finite capture radius, aims to defend a concentric perimeter from mobile intruders. The intruders are arbitrarily released at the circumference of the environment and move radially toward the perimeter with fixed speed. We present a competitive analysis approach to this problem by measuring the performance of multiple online algorithms for the vehicle against arbitrary inputs, relative to an optimal offline algorithm that has access to all future inputs. In particular, we first establish a necessary condition on the parameter space to guarantee finite competitiveness of any algorithm, and then characterize a parameter regime in which the competitive ratio is guaranteed to be at least 2 for any algorithm. We then design and analyze three online algorithms and characterize parameter regimes for which they have finite competitive ratios. Specifically, our first two algorithms are provably 1, and 2-competitive, respectively, whereas our third algorithm exhibits a finite competitive ratio that depends on the problem parameters. Finally, we provide numerous parameter space plots providing insights into the relative performance of our algorithms.
A conflict between rational and autonomous agents is considered. The paper addresses a differenti... more A conflict between rational and autonomous agents is considered. The paper addresses a differential game of protecting a target in the 3-D space. This problem highlights the strong correlation between the highly dynamic scenario, the uncertainty on the behavior of the adversary, and the online and robust computation of state-feedback strategies which guarantee the required level of performance of each player. This work significantly expands previous results around this problem by providing the players' state-feedback saddle-point strategies. Additionally, the continuously differentiable Value function of the multi-agent differential game is obtained and it is shown to be the solution of the Hamilton-Jacobi-Isaacs equation. Finally, the Barrier surface is explicitly obtained and illustrative examples highlight the robustness properties and the guarantees provided by the saddle-point strategies obtained in this paper.
In the current investigation, a guided meditation technique was designed to reach the spiritual a... more In the current investigation, a guided meditation technique was designed to reach the spiritual aspect of the inner consciousness in order to receive its influence and by being able to think according to sustainable patterns. During the meditation and through a marketing process, participants selected the best options of products or services which fit their spiritual concerns. In the end, participants discovered ways to do business by taking care of the environment and by being able to feel joy due to the approach they had with their inner spiritual aspect.
Se aspira a clarificar la posición del rey en el sistema constitucional español, descifrando el s... more Se aspira a clarificar la posición del rey en el sistema constitucional español, descifrando el significado de la fórmula «árbitro y moderador» recogida en el art. 56 de la Constitución al amparo de la idea de neutralidad. Para ello, se procede, primero, a ojear la posición del monarca surgido de la transición política a través de sus caracteres constitucionales, y segundo a efectuar un rastreo en los supuestos de la teoría del Estado Constitucional, a fin de establecer las categorías que pudieran ser coherentes con los valores democráticos. En base al fundamento que depara esta categorización se llega a la conclusión de que en el actual momento político español, no cabe otro modelo creíble que el que se corresponde con «la republicana coronada», advirtiendo, al tiempo, que la verdadera clave del problema reside no tanto en la existencia de modelos alternativos cómo y en términos de Locke, en su «reasonablessnes», esto es, en la plausibilidad o credibilidad social que sea capaz de c...
En el presente artículo se plantea una crítica a la tesis que define la Transición política españ... more En el presente artículo se plantea una crítica a la tesis que define la Transición política española como un exitoso intento de poner punto final a la “ley del péndulo” que había venido rigiendo nuestra historia constitucional. Por un lado, esta tesis minusvalora las condiciones de la situación española de 1978, marcada por el tránsito entre dos mundos, el moderno que heredaba y el emergente postmoderno, que se convertiría en una realidad incuestionable a partir de 1989. Además, la Constitución española de 1978 se redactó en un momento en que estaban declinando los supuestos conceptuales político-normativos del paradigma constitucional dominante en Europa tras la Segunda Guerra Mundial
The two-dimensional nature of mammography makes estimation of the overall breast density challeng... more The two-dimensional nature of mammography makes estimation of the overall breast density challenging, and estimation of the true patient-specific radiation dose impossible. Digital breast tomosynthesis (DBT), a pseudo-3D technique, is now commonly used in breast cancer screening and diagnostics. Still, the severely limited 3rd dimension information in DBT has not been used, until now, to estimate the true breast density or the patient-specific dose. In this study, we propose a reconstruction algorithm for DBT based on deep learning specifically optimized for these tasks. The algorithm, which we name DBToR, is based on unrolling a proximal primal-dual optimization method, where the proximal operators are replaced with convolutional neural networks and prior knowledge is included in the model. This extends previous work on a deep learning based reconstruction model by providing both the primal and the dual blocks with breast thickness information, which is available in DBT. Training and testing of the model were performed using virtual patient phantoms from two different sources. Reconstruction performance, as well as accuracy in estimation of breast density and radiation dose, was estimated, showing high accuracy (density < ±3%; dose < ±20%), without bias, significantly improving on the current state-of-the-art. This work also lays the groundwork for developing a deep learning-based reconstruction algorithm for the task of image interpretation by radiologists.
Intensity-based registration algorithms have been widely used in medical image applications. This... more Intensity-based registration algorithms have been widely used in medical image applications. This type of registration algorithms uses an object function to compute a transformation and optimizes a measure of similarity between the images being registered. The most common similarity metrics used in registration are sum of squared differences, mutual information and normalized cross-correlation. This paper aims to compare these similarity metrics, using common registration algorithms applied to breast density maps registration. To evaluate the results, we use the protocols for evaluation of similarity measures proposed byŠkerl et al. They consist in defining a set of random directions in the parameter space of the registration algorithm and compute statistical measures, such as the accuracy, capture range, number of maxima and risk of non-convergence, along these directions. The obtained results show a better performance corresponding to normalized cross-correlation for the rigid registration algorithm, while the sum of squared difference obtains the best result for the B-Spline method.
In this paper an N-pursuer vs. M-evader team conflict is studied. The differential game of border... more In this paper an N-pursuer vs. M-evader team conflict is studied. The differential game of border defense is addressed and we focus on the game of degree in the region of the state space where the pursuers are able to win. This work extends classical differential game theory to simultaneously address weapon assignments and multi-player pursuit-evasion scenarios. Saddle-point strategies that provide guaranteed performance for each team regardless of the actual strategies implemented by the opponent are devised. The players' optimal strategies require the co-design of cooperative optimal assignments and optimal guidance laws. A representative measure of performance is proposed and the Value function of the game is obtained. It is shown that the Value function is continuous, continuously differentiable, and that it satisfies the Hamilton-Jacobi-Isaacs equation-the curse of dimensionality is overcome and the optimal strategies are obtained. The cases of N = M and N > M are considered. In the latter case, cooperative guidance strategies are also developed in order for the pursuers to exploit their numerical advantage. This work provides a foundation to formally analyze complex and high-dimensional conflicts between teams of N pursuers and M evaders by means of differential game theory. This work has been supported in part by AFOSR LRIR No. 18RQCOR036.
Se trata de tomar como hilo conductor la lectura que Manuel García- Pelayo hace del pensamiento d... more Se trata de tomar como hilo conductor la lectura que Manuel García- Pelayo hace del pensamiento de Maquiavelo, para reflexionar acerca de la conveniencia de efectuar una reflexión sobre nuestra vida política desde la Teoría del Estado constitucional. La Teoría del Estado parece ser una categoría prescindible para los actuales estudiosos de la Constitución, cuando los problemas a que asistimos no pueden ser satisfactoriamente explicados acudiendo sólo a las explicaciones que nos dan las normas del Derecho. Por eso se hace necesario considerar lo que ahora están diciendo los autores de Cambridge (Pocock, Dunn, Skinner, Tuck, Pagden) para saber si es posible reconstruir una Teoría del Estado que satisfaga las deficiencias del Derecho Constitucional para abordar una realidad política que parece desbordada por los problemas de la gobernabilidad, el declive de la libertad política o la corrupción
FORO. Revista de Ciencias Jurídicas y Sociales, Nueva Época, 2019
Se elabora una propuesta para incardinar los textos políticos discursivos dentro del mundo del De... more Se elabora una propuesta para incardinar los textos políticos discursivos dentro del mundo del Derecho constitucional, especialmente dentro de su enseñanza.
Breast magnetic resonance imaging (MRI) and X-ray mammography are two image modalities widely use... more Breast magnetic resonance imaging (MRI) and X-ray mammography are two image modalities widely used for early detection and diagnosis of breast diseases in women. The combination of these modalities, traditionally done using intensity-based registration algorithms, leads to a more accurate diagnosis and treatment, due to the capability of co-localizing lesions and susceptibles areas between the two image modalities. In this work, we present the first attempt to register breast MRI and X-ray mammographic images using intensity gradients as the similarity measure. Specifically, a patient-specific biomechanical model of the breast, extracted from the MRI image, is used to mimic the mammographic acquisition. The intensity gradients of the glandular tissue are directly projected from the 3D MRI volume to the 2D mammographic space, and two different gradient-based metrics are tested to lead the registration, the normalized cross-correlation of the scalar gradient values and the gradient correlation of the vectoral gradients. We compare these two approaches to an intensity-based algorithm, where the MRI volume is transformed to a synthetic computed tomography (pseudo-CT) image using the partial volume effect obtained by the glandular tissue segmentation performed by means of an Expectation-Maximization algorithm. This allows us to obtain the digitally reconstructed radiographies by a direct intensity projection. The best results are obtained using the scalar gradient approach along with a transversal isotropic material model, obtaining a target registration error (TRE), in millimeters, of 5.65 ± 2.76 for CC-and of 7.83 ± 3.04 for MLO-mammograms, while the TRE is 7.33 ± 3.62 in the 3D MRI. We also evaluate the effect of the glandularity of the breast as well as the landmark position on the TRE, obtaining moderated correlation values (0.65 and 0.77 respectively), concluding that these aspects need to be considered to increase the accuracy in further approaches.
Medical Imaging 2017: Physics of Medical Imaging, 2017
Scattered radiation is an undesired signal largely present in most digital breast tomosynthesis (... more Scattered radiation is an undesired signal largely present in most digital breast tomosynthesis (DBT) projection images as no physically rejection methods, i.e. anti-scatter grids, are regularly employed, in contrast to fullfield digital mammography. This scatter signal might reduce the visibility of small objects in the image, and potentially affect the detection of small breast lesions. Thus accurate scatter models are needed to minimise the scattered radiation signal via post-processing algorithms. All prior work on scattered radiation estimation has used a rigid breast compression paddle (RP) and reported large contribution of scatter signal from RP in the detector. However, in this work, flexible paddles (FPs) tilting from 0 • to 10 • will be studied using Monte Carlo simulations to analyse if the scatter distribution differs from RP geometries. After reproducing the Hologic Selenia Dimensions geometry (narrow angle) with two (homogeneous and heterogeneous) compressed breast phantoms, results illustrate that the scatter distribution recorded at the detector varies up to 22% between RP and FP geometries (depending on the location), mainly due to the decrease in thickness of the breast observed for FP. However, the relative contribution from the paddle itself (3-12% of the total scatter) remains approximately unchanged for both setups and their magnitude depends on the distance to the breast edge.
Virtual clinical trials (VCT) currently represent key tools for breast imaging optimisation, espe... more Virtual clinical trials (VCT) currently represent key tools for breast imaging optimisation, especially in two-dimensional planar mammography and digital breast tomosynthesis. Voxelised breast models are a crucial part of VCT as they allow the generation of synthetic image projections of breast tissue distribution. Therefore, realistic breast models containing an accurate representation of women breasts are needed. Current voxelised breast models show, in their compressed version, a very round contour which might not be representative of the entire population. This work pretends to develop an imaging framework, based on depth cameras, to investigate breast deformation during mammographic compression. Preliminary results show the feasibility of depth sensors for such task, however post-processing steps are needed to smooth the models. The proposed framework can be used in the future to produce more accurate compressed breast models, which will eventually generate more realistic images in VCT.
2012 IEEE 51st IEEE Conference on Decision and Control (CDC), 2012
A new architecture for model-based control of unstable and uncertain systems with network induced... more A new architecture for model-based control of unstable and uncertain systems with network induced delays, and for set-point tracking over networks, is presented in this paper. This setup provides better performance than similar approaches in terms of steady-state tracking error and reduction of network traffic by transmitting measurement updates only when necessary. The results in this paper also extend previous work using the Model-Based Networked Control Systems (MB-NCS) approach to consider the output feedback case and to consider models and uncertain systems which do not necessarily have the same dimension;; that is, both the parameters and the order of the system are unknown. The Model-Based Event-Triggered (MB-ET) framework presented in this paper is used for stabilization and tracking of piece-wise constant signals and it is extended in two directions;; first, to consider a more general two channel networked system and second, to address the reference input tracking problem in the presence of network induced delays.
Proceedings of the 2011 American Control Conference, 2011
In this paper Model Based Networked Control Systems (MB-NCS) are considered and on-line identific... more In this paper Model Based Networked Control Systems (MB-NCS) are considered and on-line identification of system parameters in state space representation is used to upgrade the model and the controller of the system. The updated model is used to control the real system when feedback information is unavailable. The Extended Kalman Filter (EKF) is analyzed in the context of parameter identification and implemented in the MB-NCS framework. Emphasis is placed on global asymptotic estimators for the case when sensors provide noiseless measurements of the state of a linear system; it can be shown that the identification of parameters in this case is a linear problem, in contrast to the nonlinear combined stateparameter estimation problem. We propose new estimation models that offer better convergence properties than the EKF in this case. This estimation strategy is also applied to the MB-NCS framework resulting in a better usage of the network by allowing longer intervals without need for a measurement update.
Design of optimal controllers for uncertain linear systems subject to communication constraints i... more Design of optimal controllers for uncertain linear systems subject to communication constraints is investigated in this paper. By following the Model-Based Event-Triggered (MB-ET) control framework we are able to design optimal control laws using the nominal models that are robust to model uncertainties and limited communication. For finite horizon optimal control problems we also provide sub-optimal schedulers that estimate the best time instants to send feedback measurements. The nominal optimal controller and sub-optimal scheduler aim at optimizing the performance of the system that considers the control effort as well as the cost of communication both in the presence of model uncertainties.
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Papers by Eloy García