Gerardo Ivar Sanchez-Ortiz

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Simulating cardiac electromechanical activity is of great interest for a better understanding of pathologies and for therapy planning. Design and validation of such models is difficult due to the lack of clinical data. XMR systems are a new type of interventional facility in which patients can be rapidly transferred between X-ray and MR systems. Ou...

Radio-frequency (RF) ablation uses electrode-catheters to destroy abnormally conducting myocardial areas that lead to potentially lethal tachyarrhythmias. The procedure is normally guided with x-rays (2D), leading to errors in location and excessive radiation exposure. One of our goals is to provide pre- and intra-operative 3D MR guidance in XMR sy...

Tachyarrhythmias are pathological fast heart rhythms often caused by abnormally conducting myocardial areas (foci). Treatment by radio-frequency (RF) ablation uses electrode-catheters to monitor and destroy foci.The procedure is normally guided with x-rays (2D), and thus prone to errors in location and excessive radiation exposure. Our main goal is...

In this paper an automatic atlas-based segmentation algorithm for 4D cardiac MR images is proposed. The algorithm is based on the 4D extension of the expectation maximisation (EM) algorithm. The EM algorithm uses a 4D probabilistic cardiac atlas to estimate the initial model parameters and to integrate a priori information into the classification p...

In this paper, we present a technique that can be used to transform the motion or deformation fields defined in the coordinate system of one subject into the coordinate system of another subject. Such a transformation accounts for the differences in the coordinate systems of the two subjects due to misalignment and size/shape variation, enabling th...

Simulating cardiac electromechanical activity is of great interest for a better understanding of pathologies and therapy planning. Design and validation of such models is difficult due to the lack of clinical data. XMR systems are a new type of interventional facility in which patients can be rapidly transferred between x-ray and MR systems. Our go...

A novel method for the estimation of areas in 2D MR images of the aorta is presented. The method uses spatio-temporal non-rigid registration in order to obtain the 2D deformation fields of the vessels during the cardiac cycle. This is accomplished by aligning all time frames in the image sequence simultaneously to the first one. The determinant of...

Measuring changes in cardiac motion patterns can assist in diagnosing the onset of arrhythmia and ischaemia and in the follow-up of treatment. This work presents a methodology for measuring such motion changes from MR images. Non-rigid registration is used to track cardiac motion in a sequence of 3D tagged MR images. We use a cylindrical coordinate...

XMR systems are a new type of interventional facility in which patients can be rapidly transferred between x-ray and MR systems on a floating table. We have previously developed a technique to register MR and x-ray images obtained from such systems. We are carrying out a program of XMR guided cardiac electrophysiology study (EPS) and radio frequenc...

Measuring changes in cardiac motion patterns can assist in diagnosing the onset of arrhythmia and ischaemia and in the follow-up of treatment. This work presents a methodology for measuring such motion changes from MR images. Non-rigid registration is used to track cardiac motion in a sequence of 3D tagged MR images. We use a cylindrical coordinate...

In this paper we describe the construction of 4D atlas of human heart using cardiac MR imaging. This probabilistic atlas captures the cardiac anatomy and function of a healthy heart. In order to build the atlas we have acquired tagged as well as untagged MR image sequences from 11 healthy volunteers. The untagged MR image sequences for each subject...

Radio-frequency (RF) ablation uses electrode-catheters to destroy abnormally conducting myocardial areas that lead to potentially lethal tachyarrhythmias. The procedure is normally guided with X-rays (2D), leading to errors in location and excessive radiation exposure. In order to provide preand intraoperative 3D MR guidance, we define a probabilis...

We describe a registration and tracking technique to integrate cardiac X-ray images and cardiac magnetic resonance (MR) images acquired from a combined X-ray and MR interventional suite (XMR). Optical tracking is used to determine the transformation matrices relating MR image coordinates and X-ray image coordinates. Calibration of X-ray projection...

We describe a registration and tracking technique to integrate cardiac x-ray images and cardiac magnetic resonance (MR) images acquired from a combined x-ray and MR interventional suite (XMR). Optical tracking is used to determine the transformation matrices relating MR and x-ray image coordinates. Calibration and tracking enable us to combine x-ra...

In this paper an automatic atlas-based segmentation algorithm for 4D cardiac MR images is proposed. The algorithm is based on the 4D extension of the expectation maximisation (EM) algorithm. The EM algorithm uses a 4D probabilistic cardiac atlas to estimate the initial model parameters and to integrate a-priori information into the classification p...

In this paper an automatic atlas-based segmentation algorithm for 4D cardiac MR images is described. The algorithm is based on the 4D extension of the expectation maximisation (EM) algorithm. The EM algorithm uses a 4D probabilistic cardiac atlas to estimate the initial model parameters and to integrate spatially-varying a-priori information into t...

In this paper we present a new technique for tracking the movement of the myocardium using a statistical model derived from the motion fields in the hearts of several healthy volunteers. To build the statistical model we tracked the motion of the myocardium in 17 volunteers using a nonrigid registration technique based on free-form deformations and...

In this paper we present a technique for constructing a cardiac motion atlas using the myocardial motion fields derived from 4D MR image sequences of a series of subjects. This is achieved by transforming the motion field of each subject into a the coordinate system of a reference subject, and then averaging the transformed fields to give a vector...

In this paper we present a technique for constructing a cardiac motion atlas using the myocardial motion fields derived from 4D MR image sequences of a series of subjects. This is achieved by transforming the motion field of each subject into a the coordinate system of a reference subject, and then averaging the transformed fields to give a vector...

We propose a novel method for fully automated segmentation and tracking of the myocardium and left and right ventricles (LV and RV) using 4D MR images. The method uses non-rigid registration to elastically deform a cardiac atlas built automatically from 14 normal subjects. The registration yields robust performance and is particularly suitable for...

We present a novel technique that enables a direct quantitative comparison of cardiac motion derived from 4D MR image sequences to be made either within or across patients. This is achieved by registering the images that describe the anatomy of both subjects and then using the computed transformation to map the motion fields of each subject into th...

A major barrier for using 3-D echocardiography for quantitative analysis of heart function in routine clinical practice is the absence of accurate and robust segmentation and tracking methods necessary to make the analysis automatic. In this paper, we present an automated three-dimensional (3-D) echocardiographic acquisition and image-processing me...

Three-dimensional (3D) and four-dimensional (4D) imaging of the heart is a rapidly developing area of research in medical imaging. Recent advances in development of MR imaging for fast spatio-temporal cardiac imaging have led to an increased interest in the use of MR imaging for functional analysis of the cardiovascular system. Segmentation of left...

A novel method for the automatic segmentation and tracking of the heart in 4D MR images is proposed. The method uses non-rigid registration to elastically deform a cardiac atlas, built automatically from 14 normal subjects, to a subject specific atlas. The subject specific atlas has been constructed by registering all the time frames to the end-dia...

3D echocardiography is a recent cardiac imaging method actively developed for quantitative analysis of heart function. A major barrier for its use as a quantitative tool in routine clinical practice is the absence of accurate and robust segmentation and tracking methods necessary to make the analysis fully automatic. In this article we present a fu...

. We present a general formulation for a new knowledge-based approach to anisotropic diffusion of multi-feature and multi-dimensional images, with an illustrative application to cardiac MRI. We incorporate all available information through a more complete definition of the conductance function which differs from previous approaches in two aspects....

We present a general formulation for a new knowledge-based approach to anisotropic diffusion of multi-valued and multi-dimensional images, with an illustrative application for the enhancement and segmentation of cardiac magnetic resonance (MR) images. In the proposed method all available information is incorporated through a new definition of the c...

We present a general formulation for a new knowledge-based approach to anisotropic diffusion of multi-valued and multi-dimensional images, with an illustrative application for the enhancement and segmentation of cardiac magnetic resonance (MR) images. In the proposed method all available information is incorporated through a new definition of the c...

Previously, we proposed a second rank tensor conductance function with an explicit dependence on the space coordinates and the data function. This scheme gives the equations an intrinsic anisotropic character not present in previous approaches, and allows the use of a priori knowledge of the system in multi-feature and multi-dimensional images. In...

. We present a general formulation for a new knowledge-based approach to anisotropic diffusion of multi-feature and multi-dimensional images, with an application to enhancement and segmentation of cardiac MR images. We incorporate all available information through a more complete definition of the conductance function which differs from previous de...

Understanding of the dynamics of the heart is required for the prevention and treatment of cardiac related diseases as well as for the design of pace-makers and artificial hearts. We present a new method for the analysis of myocardium motion and deformation based on the study of velocity encoded NMR images. By applying a few mathematical operators...

A variable-mass relaxation oscillator model for the behaviour of the leaky tap is numerically investigated. Different regions of its three dimensional parameter space have been searched and interesting dynamical behaviour has been found. The dynamics of the system is thoroughly characterized using projections of phase space trajectories, 2 and 3 di...

Knowledge of the motion and shape variability of the heart is necessary for the diagnosis and treatment of cardiac related diseases. In particular, the evaluation of the contraction of the left ventricle of the heart (myocardium) plays a key role in the assessment of ischaemia and cardiac malfunction. Among the existing non-invasive imaging techniq...

e length of the whole cardiac cycle which evidently affect the nature of the contraction-relaxation process). However, this is only an approximation [5-7]. Data collected to form an image proceed from somewhat different phases of the cardiac cycle, and the obvious consequence is the degradation of the images, particularly those of the late (diastol...

We have developed a new approach for analyzing the regional and global motion and deformation of the myocardium using density and velocity encoded cardiac MR images. First, the inner and outer wall of the left ventricle muscle are segmented in the density images. A set of homogeneously distributed points on these contours of the myocardium wall is...

We have developed a new approach for analyzing the regional motion and deformation of the myocardium. The proposed method uses density and velocity encoded cardiac MR images. First the inner and outer wall of the left ventricle muscle are segmented in the density images. A set of homogeneously distributed points on these contours of the myocardium...

. We present a general formulation for a new knowledge-based approach toanisotropic diffusion of multi-feature and multi-dimensional images, with an illustrative applicationto cardiac MRI. We incorporate all available information through a more completedefinition of the conductance function which differs from previous approaches in two aspects.Firs...

Numerical evidence for the existence of strange chaotic attractors is found in a variable-mass relaxation oscillator model for the dripping faucet. We exhibit bifurcation maps which illustrate the richness of the model dynamics; we also have found simple periodic attractors up to period-12. More complex attractors exist which, after computing their...

Radio-frequency (RF) ablation uses electrode-catheters to destroy abnormally conducting myocardial areas that lead to potentially lethal tachyarrhythmias. The procedure is normally guided with x-rays (2D), leading to errors in location and excessive radiation exposure. One of our goals is to provide pre- and intra-operative 3D MR guidance in XMR sy...

Recent advances in non-rigid motion tracking techniques that use tagged MR (SPAMM) enable us to measure more subtle changes in cardiac motion patterns due to diseases such as arrhythmia, ischaemia and infarct, as well as to follow up medical treatment and to assist surgical intervention. One such example of disease with associated changes in motion...