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IntraVascular Ultrasound (IVUS) is an exploratory technique used in interventional procedures that shows cross section images of arteries and provides qualitative information about the causes and severity of the arterial lumen narrowing. Cross section analysis as well as visualization of plaque extension in a vessel segment during the catheter imaging pullback are the technique main advantages. However, IVUS sequence exhibits a periodic rotation artifact that makes difficult the longitudinal lesion inspection and hinders any segmentation algorithm. In this paper we propose a new kinematic method to estimate and remove the image rotation of IVUS images sequences. Results on several IVUS sequences show good results and prompt some of the clinical applications to vessel dynamics study, and relation to vessel pathology. [ABSTRACT FROM AUTHOR]

Plaque analysis in IVUS planes needs accurate intima and adventitia models. Large variety in adventitia descriptors difficulties its detection and motivates using a classification strategy for selecting points on the structure. Whatever the set of descriptors used, the selection stage suffers from fake responses due to noise and uncompleted true curves. In order to smooth background noise while strengthening responses, we apply a restricted anisotropic filter that homogenizes grey levels along the image significant structures. Candidate points are extracted by means of a simple semi supervised adaptive classification of the filtered image response to edge and calcium detectors. The final model is obtained by interpolating the former line segments with an anisotropic contour closing technique based on functional extension principles. [ABSTRACT FROM AUTHOR]

Wireless endoscopy is a very recent and at the same time unique technique allowing to visualize and study the occurrence of contractions and to analyze the intestine motility. Feature extraction is essential for getting efficient patterns to detect contractions in wireless video endoscopy of small intestine. We propose a novel method based on anisotropic image filtering and efficient statistical classification of contraction features. In particular, we apply the image gradient tensor for mining informative skeletons from the original image and a sequence of descriptors for capturing the characteristic pattern of contractions. Features extracted from the endoluminal images were evaluated in terms of their discriminatory ability in correct classifying images as either belonging to contractions or not. Classification was performed by means of a support vector machine classifier with a radial basis function kernel. Our classification rates gave sensitivity of the order of 90.84% and specificity of the order of 94.43% respectively. These preliminary results highlight the high efficiency of the selected descriptors and support the feasibility of the proposed method in assisting the automatic detection and analysis of contractions. [ABSTRACT FROM AUTHOR]

Since the upturn of intravascular ultrasound (IVUS) as an imaging technique for the coronary artery system, much research has been done to simplify the complicated analysis of the resulting images. In this study, an attempt to develop an automatic tissue characterization algorithm for IVUS images was done. The first step was the extraction of texture features. The resulting feature space was used for classification, constructing a likelihood map to represent different coronary plaques. The information in this map was organized using a recently developed [1] geodesic snake formulation, the so-called Stop & Go snake. The novelty of our study lies in this last step, as it was the first time to apply the Stop & Go snake to segment IVUS images. [ABSTRACT FROM AUTHOR]

A realistic anthropomorphic numerical model of the beating heart is presented. It includes the main cardiac anatomical structures, vessels junctions and part of the coronary network. Its main feature is that it is based on an imaging study on the same human subject from which both structural and motion information are retrieved. This confers to the model a remarkable consistency. Heart's deformation is assessed through successive 3D non rigid registrations in cine MR sequences. The resulting model can be used for the evaluation of cardiac image processing algorithms such as myocardium segmentation and cardiac image registration. [ABSTRACT FROM AUTHOR]

Recent findings in a sheep model of atrial fibrillation support the hypothesis that an organized micro-reentry could be the maintaining mechanism of the arrhythmia (mother wavelet). According to these studies we constructed a two dimensional computer model of tissue in the region around a pair of pulmonary vein ostia and investigated anchoring of a reentry wave at these ostia. We used the Luo Rudy phase I ionic current model to describe membrane kinetics and generated two different stages of electrical remodelling of the cells by varying the slow inward calcium current. Our attempt to initiate a stable reentry failed for cells with higher action potential duration and higher rate adaption. By simulating a higher stadium of electrical remodelling we finally were successful, and we were able to produce a periodic reentry. This led us to the conclusion that a low rate adaption (high electrical remodelling) facilitates organized activity in the atria. [ABSTRACT FROM AUTHOR]

Basic electrical properties and electrophysiological mechanisms of cardiac tissue have been frequently researched applying preparations of papillary muscle. Advantages of these preparations are the simplicity to satisfy their metabolic demands and the geometrical elementariness in comparison to wedge and whole heart preparations. In this computational study the spatio-temporal evolution of activation fronts in papillary muscle was reconstructed with a bidomain model of electrical current flow and a realistic electrophysiological model of cardiac myocytes. The effects of two different pacing sites were investigated concerning the distribution of extracellular potentials and transmembrane voltages. Results of simulations showed significant changes of the resulting wave fronts and the related potential distributions inside of the muscle and in the bath for the different pacing sites. Additionally, the results indicated that reliable measurements of activation times can be carried out only in regions adjacent to the wave front. These results can be applied for development of measurement setups and techniques for analysis of experimental studies of papillary muscle. [ABSTRACT FROM AUTHOR]

We describe numerical simulations of spiral waves dynamics in the computational model of human atrial tissue with the Courtemanche-Ramirez-Nattel local kinetics. The spiral wave was initiated by cross-field stimulation protocol, with and without preliminary "fatigue" by rapid stimulation of the model tissue for a long time. In all cases the spiral wave has finite lifetime and self-terminates. However the mechanism of self-termination appears to depend on the initiation procedure. Spiral waves in the "fresh" tissue typically terminate after a few rotations via dissipation of the excitation front along the whole of its length. The dynamics of spiral waves in "tired" tissue is characterized by breakups and hypermeander, which also typically leads to self-termination but only after a much longer interval of time. Some features of the observed behaviour can not be explained using existing simplified theories of dynamic instabilities and alternanses. [ABSTRACT FROM AUTHOR]

The interpretation of cine-loops and parametric images to assess regional wall motion in echocardiography requires to acquire an expertise, which is based on training. To overcome the training phase for the interpretation of new parametric images, a quantification based on profiles in the parametric images was attempted. The classification of motion was performed on a training set including 362 segments and tested on a second database including 238 segments. The consensual visual interpretation of two-dimensional sequences by two experienced readers were used as the "gold standard". Mono- and multi-parametric classification approaches were undertaken. Results show an accuracy of 74% for training and 68% for test in case of mono-parametric approach. They are 80% and 67% in case of multi-parametric approach. Moreover, the evaluation protocol enables to understand the limitations of this approach. The in-depth study shows that a large part of false-positive segments are apical segments. This suggests that taking into account the segment location could improve the performances. [ABSTRACT FROM AUTHOR]

In the context of motion estimation of the heart and thoracic structures from tomographic imaging, we investigated two free form deformations (FFD) based non linear registration methods as motion estimators. Standard and cylindrical FFD (CFFD) methods are evaluated in 2D, both on simulated and in vivo cardiac and thoracic images. Results tend to show that CFFD based method achieves the same accuracy with less parameters. However, the fast convergence of this model is hamped by a higher computing time with a straightforward implantation. [ABSTRACT FROM AUTHOR]

Multislice Computed Tomography (MSCT) scanners offers new perspectives for cardiac kinetics evaluation with 3D time image sequences of high contrast and spatio-temporal resolutions. A new method is proposed for cardiac motion extraction in Multislice CT. Based on a 3D surface-volume matching process, it provides the detection of the heart left cavities along the acquired sequence and the estimation of their 3D surface velocity fields. A 3D segmentation step and surface reconstruction process are first applied on only one image of the sequence to obtain a 3D mesh representation for one t time. A Markov Random Field model is defined to find best correspondences between 3D mesh nodes at t time and voxels in the next volume at t + 1 time. A simulated annealing is used to perform a global optimization of the correspondences. First results obtained on simulated and real data show the good behaviour of this method. [ABSTRACT FROM AUTHOR]

Magnetic resonance tagging technique measures the deformation of the heart wall by overlying darker tag lines onto the brighter myocardium and tracking their motion during the heart cycle. In this paper, we propose a new spline-based methodology for constructing a dense cardiac displacement map based on the tag tracking result. In this new approach, the deformed tags are tracked using a Gabor filter-based technique and smoothed using implicit splines. Then we measure the displacement in the myocardium of both ventricles using a new spline interpolation model. This model uses rough segmentation results to set up break points along tag tracking spline so that the local myocardium deformation will not be influenced by the tag information in the blood or the deformation in other parts of the myocardium. The displacements in x- and y-directions are calculated separately and are combined later to form the final displacement map. This method accepts either a tag grid or separate horizontal and vertical tag lines as its input by adjusting the offsets of images taken at different breath hold. The method can compute dense displacement maps of the myocardium for time phases during systole and diastole. The approach has been quantatively validated on phantom images and been tested on more than 20 sets of in-vivo heart data. [ABSTRACT FROM AUTHOR]

Matrix-phased array transducers for real-time three-dimensional ultrasound enable fast, non-invasive visualization of cardiac ventricles. Segmentation of 3D ultrasound is typically performed at end diastole and end systole with challenges for automation of the process and propagation of segmentation in time. In this context, given the position of the endocardial surface at certain instants in the cardiac cycle, automated tracking of the surface over the remaining time frames could reduce the workload of cardiologists and optimize analysis of volume ultrasound data. In this paper, we applied optical flow to track the endocardial surface between frames of reference, segmented via manual tracing or manual editing of the output from a deformable model. To evaluate optical-flow tracking of the endocardium, quantitative comparison of ventricular geometry and dynamic cardiac function are reported on two open-chest dog data sets and a clinical data set. Results showed excellent agreement between optical flow tracking and segmented surfaces at reference frames, suggesting that optical flow can provide dynamic "interpolation" of a segmented endocardial surface. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of the motion fields computed from TrueFISP untagged and SPAMM tagged magnetic resonance (MR) images using a 4D nonrigid registration algorithm that we have developed for cardiac motion tracking [3]. Our results, which were obtained from a group of 7 normal volunteers, indicate that although there is a good correlation between the motion fields computed from the tagged and untagged MR images, some of the twisting motion is not captured in the motion fields derived from the TrueFISP MR images. [ABSTRACT FROM AUTHOR]

In this paper we present a novel approach to the problem of spatio-temporal alignment of cardiac MR image sequences. This novel method has the ability to correct spatial misalignment caused by global acquisition and local shape differences as well as temporal misalignment caused by differences in the length of the cardiac cycles or by differences in the motion patterns of the hearts. In contrast to our previous approach [1], the algorithm optimizes the spatial and temporal transformation components separately, thus significantly speeding up the registration process. To achieve this we have developed a novel approach for the calculation of the temporal registration which does not require the spatial alignment of the image sequences. The method was evaluated using fifteen cardiac MR image sequences from healthy volunteers and the results were compared to the previously presented method. The results indicate that the performance of the method is similar to the previously presented method [1] while the the computational complexity has been significantly reduced. [ABSTRACT FROM AUTHOR]

Many models of the cardiovascular system (e.g. cardiac electrical activity, autonomous nervous system, ...) have been proposed for the last decades. Research is now focusing on the integration of these different models, in order to study more complicated physiopathological states in clinical applications context. To get round the practical limitations of existing models, multi-formalism modelling appears as a way to ease the integration of these different models together. This paper presents an original methodology allowing to combine different types of description formalisms. This method has been applied to define a multi-formalism model of cardiac action potential propagation on a 2D grid of endocardial cells, combining cellular automata and a set of cells defined by the Beeler-Reuter model. Results, obtained under physiologic and ischemic conditions, highlight the improvements in term of computing compared with mono-formalism systems, while keeping the necessary explanatory strength for a practical clinical use. [ABSTRACT FROM AUTHOR]

The non invasive evaluation of the cardiac function presents a great interest for the diagnosis of cardiovascular diseases. Tagged cardiac MRI allows the measurement of anatomical and functional myocardial parameters. This protocol generates a dark grid which is deformed with the myocardium displacement on both Short-Axis (SA) and Long-Axis (LA) frames in a time sequence. Tracking the grid allows the estimation of the displacement inside the myocardium. The work described in this paper aims to make the automatic tracking of the grid of tags on cardiac MRI sequences robust and reliable, thanks to an informational formalism based on Extreme Physical Informational (EPI). This approach leads to the development of an original diffusion pre-processing allowing us to increase significantly the robustness of the detection and the follow-up of the grid of tags. [ABSTRACT FROM AUTHOR]

Heart ventricular mechanics has been investigated intensively in the last four decades. The passive material properties, the ventricular geometry and muscular architecture, and the myocardial activation are among the most important determinants of cardiac mechanics. The heart muscle is anisotropic, inhomogeneous, and highly nonlinear. The heart ventricular geometry is irregular and object dependent. The muscular architecture includes the organization of the fiber and the connective tissues. Studies of the myocardial activation have been carried out at both cell and tissue levels. Previous work from our research group has successfully estimated the in-vivo motion and deformation of both the left and the right ventricles. In this paper, we present an iterative model to estimate the in-vivo myocardium material properties, the active forces generated along fiber orientation, and strain and stress distribution in both ventricles. Compared to the strain energy function approach, our model is more intuitively understandable. Using the model, we have simulated the mechanical events of a few different heart diseases. Noticeable strain and stress differences are found between normal and diseased hearts. [ABSTRACT FROM AUTHOR]

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 systems (combined X-ray and MRI room) by locating myocardial regions with abnormal electrical conduction patterns. We address the inverse electro-mechanical relation by using motion in order to infer electrical propagation. For this purpose we define a probabilistic measure of the onset of regional myocardial activation derived from motion fields. The 3D motion fields are obtained using non-rigid registration of tagged MR sequences to track the heart. The myocardium is subdivided in segments and the derived activation isochrones maps compared. We also compare regional motion between two different image acquisitions, thus assisting in diagnosing arrhythmia, in follow up of treatment, and particularly in determining whether the electro-physiological intervention succeeded. We validate our methods using an electro-mechanical model of the heart, synthetic data from a cardiac motion simulator for tagged MRI, a cardiac MRI atlas of motion and geometry, MRI data from 6 healthy volunteers (one of them subjected to stress), and an MRI study on one patient with tachyarrhythmia, before and after RF ablation. Results seem to corroborate that the ablation had the desired effect of regularising cardiac contraction. [ABSTRACT FROM AUTHOR]

We evaluated applicability of ICA (Independent Component Analysis) for the separation of functional components from H215O PET (Positron Emission Tomography) cardiac images. The effects of varying myocardial perfusion to the separation results were investigated using a dynamic 2D numerical phantom. The effects of motion in cardiac region were studied using a dynamic 3D phantom. In this 3D phantom, the anatomy and the motion of the heart were simulated based on the MCAT (Mathematical Cardiac Torso) phantom and the image acquisition process was simulated with the PET SORTEO Monte Carlo simulator. With ICA, it was possible to separate the right and left ventricles in the all tests, even with large motion of the heart. In addition, we extracted the ventricle volumes from the ICA component images using the Deformable Surface Model based on Dual Surface Minimization (DM-DSM). In the future our aim is to use the extracted volumes for movement correction. [ABSTRACT FROM AUTHOR]

In this article, we present a framework to estimate local myocardium contractility using clinical MRI, a heart model and data assimilation. First, we build a generic anatomical model of the ventricles including muscle fibre orientations and anatomical subdivisions. Then, this model is deformed to fit a clinical MRI, using a semi-automatic fuzzy segmentation, an affine registration method and a local deformable biomechanical model. An electromechanical model of the heart is then presented and simulated. Data assimilation makes it possible to estimate local contractility from given displacements. Presented results on adjustment to clinical data and on assimilation with simulated data are very promising. Current work on model calibration and estimation of patient parameters open up possibilities to apply this framework in a clinical environment. [ABSTRACT FROM AUTHOR]

Mathematical modeling of cardiac mechanics could be a useful clinical tool, both in translating measured abnormalities in cardiac deformation into the underlying pathology, and in selecting a proper treatment. We investigated to what extent a previously published model of cardiac mechanics [6] could predict deformation in the healthy left ventricle, as measured using MR tagging. The model adequately predicts circumferential strain, but fails to accurately predict shear strain. However, the time course of shear strain proves to be that sensitive to myofiber orientation, that agreement between model predictions and experiment may be expected if fiber orientation is changed by only a few degrees. [ABSTRACT FROM AUTHOR]

One mechanism for the onset of arrhythmias is abnormal impulse initiation such as ventricular ectopic beats. These may be caused by abnormal calcium (Ca2+) cycling. The Luo-Rudy model was used to simulate the dynamics of intracellular Ca2+ ([Ca2+]i) handling and the initiation of ectopic beats in virtual ventricular myocytes and tissues. [Ca2+]i in the reduced Ca2+ handling equations settles to a steady state at low levels of intracellular sodium ([Na+]i), but oscillates when [Na+]i is increased. These oscillations emerge through a homoclinic bifurcation. In the whole cell, Ca2+ overload, brought about by inhibition of the sodium-potassium pump and elevated [Na+]i, can cause autorhythmic depolarisations. These oscillations interact with membrane currents to cause action potentials that propagate through one dimensional virtual tissue strands and two dimensional anisotropic virtual tissue sheets. [ABSTRACT FROM AUTHOR]

Numerical simulations of re-entrant waves in detailed ionic models reveal a phenomenon that is impossible in traditional simplified mathematical models of FitzHugh-Nagumo type: dissipation of the excitation front (DEF). We have analysed the structure of three selected ionic models, identified the small parameters that appear in non-standard ways, and developed an asymptotic approach based on those. Contrary to a common belief, the fast Na current inactivation gate h is not necessarily much slower than the transmembrane voltage E during the upstroke of the action potential. Interplay between E and h is responsible for the DEF. A new simplified model emerges from the asymptotic analysis and considers E and h as equally fast variables. This model reproduces DEF and admits analytical study. In particular, it yields conditions for the DEF. Predictions of the model agree with the results of direct numerical simulations of spiral wave break-up in a detailed model. [ABSTRACT FROM AUTHOR]

To investigate the quantitative abnormalities induced by prior myocardial infarction (MI) on the whole electrical cardiac cycle, body surface potential mapping was recorded in 144 patients with prior MI and 75 healthy controls. QRS onset, offset and T-wave end were automatically determined from the averaged signal. Time integrals were calculated for the QRS wave and the STT wave. In MI patient group the average QRS and STT integrals showed strong negative correlation on the body surface (r = - 0.901, p < 0.001) in contrast to the positive correlation in the control group (r = 0.285, p < 0.001). Sensitivity of an inverted QRS / STT integral relation to detect MI was 79%, as opposed to the sensitivity of the descriptive Minnesota code of 70%. Furthermore the degree of inversion correlated with left ventricular ejection fraction thus relating to the size of MI. [ABSTRACT FROM AUTHOR]

Large scale simulations of an anisotropic and heterogeneous cardiac model in three dimensional myocardial blocks are presented. The Monodomain tissue representation used includes orthotropic anisotropy, intramural fiber rotation and homogeneous or heterogeneous intramural Luo-Rudy I membrane ionic models. Simulations of the entire QT interval for epicardial and endocardial pacing show that the effect of intramural heterogeneity on the dispersion of the action potential duration is mostly discernible along the epi- endocardial direction, while in the orthogonal directions the dispersion patterns have the same qualitative features of the homogeneous model. [ABSTRACT FROM AUTHOR]

In this article we study the problem of estimating the parameters of a 2-D electrophysiological model of the heart from a set of temporal recordings of extracellular potentials. The chosen model is the reaction-diffusion model on the action potential proposed by Aliev and Panfilov. The strategy consists in building an error criterion based upon a comparison of depolarization times between the model and the measures. This error criterion is minimized in two steps : first a global and then a local adjustment of the model parameters. The feasibility of the approach is demonstrated on real measures on canine hearts, showing also the necessity to introduce anisotropy and probably a third spatial dimension in the model. [ABSTRACT FROM AUTHOR]

The dangerous cardiac arrhythmias of tachycardia and fibrillation are most often sustained by re-entry. Re-entrant waves rotate around a phase singularity, and the identification and tracking of phase singularities allows the complex activity observed in both experimental and computational models of fibrillation to be quantified. In this paper we present preliminary results that compare two methods for identifying phase singularities in a computational model of fibrillation in 2 spatial dimensions. We find that number of phase singularities detected using each method depends on choosing appropriate parameters for each algorithm, but that if an appropriate choice is made there is little difference between the two methods. [ABSTRACT FROM AUTHOR]

Cardiovascular diseases are a major health concern all over the world and, especially, heart failure has gained more importance in the recent years. Improving diagnosis and therapy is therefore critical and among the several resources at our disposal, implantable devices is expected to have a better rate of success. This paper is focused on two topics: (i) our views of the main challenges to face in order to reach these objectives and (ii) a specific target regarding the pose of leads for multisite pacemakers by means of virtual endoscopy pre-operative planning and path finding throughout the coronary venous tree. [ABSTRACT FROM AUTHOR]

The stability of induced pacemaker activity in a virtual human ventricular cell is analysed by numerical simulations and continuation algorithms, with the conductance of the time independent inward rectifying potassium current (IK1) as the bifurcation parameter. Autorhythmicity is induced within a narrow range of this conductance, where periodic oscillations and bursting behaviour are observed. The frequency of the oscillations approaches zero as the parameter moves towards the bifurcation point, suggesting a homoclinic bifurcation. Intracellular sodium ([Na+]i) and calcium ([Ca2+]i) concentration dynamics can influence the location of the bifurcation point and the stability of the periodic states. These two concentrations function as slow variables, pushing the fast membrane voltage system into and out of the periodic region, producing bursting behaviour. Moreover, suppressing IK1 will prolong action potential duration and may introduce risks of developing stable periodic intermittency and arrhythmia. A genetically engineered pacemaker may appear an attractive idea, but simple analysis suggests inherent problems. [ABSTRACT FROM AUTHOR]

Rett syndrome (RS) is a severe neurological disorder, predominant in females, with higher risk of sudden death (SD). So far for risk-assessment, heart rate variability (HRV), QT duration and its dispersion (QTd) were measured with ECG. However SD has occurred in RS also in absence of ECG abnormality. We aimed to evaluate the feasibility of magnetocardiographic (MCG) mapping as an alternative to study ventricular repolarization (VR) alteration in RS patients. 9 female (age: 1-34 years) RS patients were studied with an unshielded 36-channels MCG system. To assess VR, heart rate (HR)-corrected JTpeak, JTend, QTend, Tpeak-endintervals and QTd, were measured from both MCG and ECG signals. Moreover the magnetic field (MF) gradient orientation (α-angle) during the ST segment and three MF dynamic parameters were automatically evaluated from MCG T-wave. HRV parameters were evaluated from 12-lead Holter ECG. 15 age-matched normal controls (NC) were studied for comparison. HR-corrected JTpeak, JTend, QTend and Tpeak-end intervals, and QTd were longer in RS than in NC. The differences were more evident with clinical impairment (stage IV). MF gradient orientation and MF dynamic parameters were abnormal in RS patients. As compared to NC, HRV parameters were altered in the time-domain, although still within normal range in the frequency-domain. In RS, ECG recordings are often noisy and BSPM is difficult. On the contrary MCG mapping is easily feasible and discovers VR alteration not evident at the ECG. The diagnostic value of MCG in RS remains to be defined. [ABSTRACT FROM AUTHOR]

Electrophysiological heterogeneity within human ventricles is mainly based on differences of ion channel characteristics inside the wall. This influences also properties of cellular tension development. In this work, knowledge about transmural heterogeneity was transferred to an electro-mechanical heart model composed of a human model describing electrophysiology and of a model for the development of tensions. The heterogeneity was included in the cardiomyocyte model by varying ion channel kinetics and density on basis of measured data. The properties of the heterogeneous electro-mechanical model were demonstrated in a realistic model of left ventricular geometry and fiber orientation using a monodomain approach for describing electrical interaction. This study indicated the necessity of incorporating regional heterogeneity to model human cardiac electro-mechanics with qualitative good agreement to measured data. The heterogeneity leads to a homogenization of the mechanical process due to increasing time to peak tension from epicardium towards endocardium. [ABSTRACT FROM AUTHOR]

We report on an investigation into using a Level Sets based method to reconstruct activation wavefronts at each time instant from measured potentials on the body surface. The potential map on the epicardium is approximated by a two level image and the inverse problem is solved by evolving a boundary, starting from an initial region, such that a filtered residual error is minimized. The advantage of this method over standard activation-based solutions is that no isotropy assumptions are required. We discuss modifications of the Level Sets method used to improve accuracy, and show the promise of this method via simulation results using recorded canine epicardial data. [ABSTRACT FROM AUTHOR]

Effects of pathophysiological conditions and pharmacological intervention on transmural propagation are computed for the virtual ventricular wall. ST depression during sub-endocardial ischaemia and unidirectional functional block in the vulnerable window during Class III drug action are explained by changes induced in the transmural dispersion of action potential duration. [ABSTRACT FROM AUTHOR]

Left ventricular hypertrophy induces remodeling of various ion channels and prolongs depolarization of the ventricles. We modified a model of electrical activity of rat ventricular cell by incorporating available experimental data. Hypertrophy was modeled by incorporating experimental data of changes in sodium (INa), hyperpolarizing (If), outward transient potassium (Ito) and T-type calcium currents channel kinetics (ICaT), cell size and Ca2+ handling. In 1D simulations, a continuous increase in action potential duration (APD) and corresponding decrease in conduction velocity (CV) with subsequent beats was observed, resulting in conduction block at low values of stimulus intervals (SI), for which the simulated action potential (AP) restitution of the cell models has negative slope. [ABSTRACT FROM AUTHOR]

Magnetocardiographic (MCG) mapping measures magnetic fields generated by the electrophysiological activity of the heart. Quantitative analysis of MCG ventricular repolarization (VR) parameters may be useful to detect myocardial ischemia in patients with apparently normal ECG. However, manual calculation of MCG VR is time consuming and can be dependent on the examiner's experience. Alternatively, the use of machine learning (ML) has been proposed recently to automate the interpretation of MCG recordings and to minimize human interference with the analysis. The aim of this study was to validate the predictive value of ML techniques in comparison with interactive, computer-aided, MCG analysis. ML testing was done on a set of 140 randomly analysed MCG recordings from 74 subjects: 41 patients with ischemic heart disease (IHD) (group 1), 32 of them untreated (group 2), and 33 subjects without any evidence of cardiac disease (group 3). For each case at least 2 MCG datasets, recorded in different sessions, were analysed. Two ML techniques combined identified abnormal VR in 25 IHD patients (group 1) and excluded VR abnormalities in 28 controls (group 3) providing 75% sensitivity, 85% specificity, 83% positive predictive value, 78% negative predictive value, 80% predictive accuracy This result was for the most part in agreement, but statistically better than that obtained with interactive analysis. This study confirms that ML, applied on MCG recording at rest, has a predictive accuracy of 80% in detecting electrophysiological alterations associated with untreated IHD. Further work is needed to test the ML capability to differentiate VR alterations due to IHD from those due to non-ischemic cardiomyopathies. [ABSTRACT FROM AUTHOR]

Calcified coronary arteries can cause severe cardiac problems and may provoke an infarction of the heart's wall. An established treatment method is the bypass operation. The usage of a telemanipulation system allows for the execution of that operation as a totally endoscopic coronary artery bypass (TECAB) grafting. This relatively new method narrows the surgeon's view and does not permit the palpation of the vessel in order to detect calcifications (hard plaques). A planning based on contrast enhanced, cardiac CT data sets can compensate for that problem. This work presents analysis methods for coronary arteries. Hard plaques are detected using a tracking-based vessel segmentation technique. In addition, the vessel's neighborhood is analyzed in order to decide whether it is surrounded by tissue or fat, or if it is freely accessible for the surgeon's instruments. Furthermore, well adapted methods for the visualization of these analysis results are presented. Keywords: Coronary arteries, vessel segmentation, calcification detection, minimally invasive surgery, cardiac imaging, computed tomography. [ABSTRACT FROM AUTHOR]

Segmentation of the fetal heart can facilitate the 3D assessment of the cardiac function and structure. Ultrasound acquisition typically results in drop-out artifacts of the chamber walls. This paper presents a level set deformable model to simultaneously segment all four cardiac chambers using region based information. The segmented boundaries are automatically penalized from intersecting at walls with signal dropout. Root mean square errors of the perpendicular distances between the algorithm's delineation and manual tracings are within 7 pixels (<2mm) in 2D and under 3 voxels (<4.5mm) in 3D. The ejection fraction was determined from the 3D dataset. Future work will include further testing on additional datasets and validation on a phantom. [ABSTRACT FROM AUTHOR]

Domain knowledge about the geometrical properties of cardiac structures is an important ingredient for the segmentation of those structures in medical images or for the simulation of cardiac physiology. So far, a strong focus was put on the left ventricle due to its importance for the general pumping performance of the heart and related functional indices. However, other cardiac structures are of similar importance, e.g. the coronary arteries with respect to diagnosis and treatment of arteriosclerosis or the left atrium with respect to the treatment of atrial fibrillation. In this paper we describe the generation of a comprehensive geometric cardiac model including the four cardiac chambers and the trunks of the connected vasculature, as well as the coronary arteries and a set of cardiac landmarks. A mean geometric model has been built. A general process to add inter-individual and temporal variability is proposed and will be added in a second stage. [ABSTRACT FROM AUTHOR]

For the analysis of shape variations of the heart and the cardiac motion in a clinical environment it is necessary to segment a large amount of data in order to be able to build statistically significant models. Therefore it has been the aim of this project to find and develop methods that allow the creation of a fully automatic segmentation pipeline for the segmentation of endocardium and myocardium in ECG-triggered MRI images. For this purpose a combination of a number of image processing techniques, from the fields of segmentation, modeling and image registration have been used and extended to create a segmentation pipeline that reduces the need for supplementary manual correction of the segmented labels to a minimum. [ABSTRACT FROM AUTHOR]

Different methods were evaluated to enlarge artificially a training set which is used to build a statistical shape model. In this work, the shape model was built from MR data of 25 subjects and it consisted of ventricles, atria and epicardium. The method adding smooth non-rigid deformations to original training set examples produced the best results. The results indicated also that artificial deformation modes model better an unseen object than an equal number of standard PCA modes generated from original data. [ABSTRACT FROM AUTHOR]

A procedure for helping the professional in electrophysiology in performing catheter ablation as a definitive treatment of certain types of arrythmia is presented here. This procedure uses trajectory planning techniques that have been developed in the robotics field. Starting off from signals obtained in an electrophysiological study of a patient, an electrical model of the heart with zones of different propagation properties is generated. Trajectory planning techniques are used to obtain the qualitative behavior of the heart under different types of arrythmia. A good point for ablation is computed as one that interrupts the trajectory that is sustaining the arrythmia. [ABSTRACT FROM AUTHOR]

We developed a 3D computer graphic model of functional anatomy of the human heart. The model provides visually correct anatomical and functional detail suitable for medical education. We reconstructed 3D surface models of the human heart based on segmentation obtained from the Visible Human image datasets. We developed a fiber based muscle action model specially adapted for the myocardium. Each muscle fiber is equipped with contractile and elastic elements and is used as a local shape deformation guide. The timing of fiber contraction activation is driven by patient specific action potential excitation patterns. As a first step we have visualized the function of a healthy heart. We are now planning to visualize a range of cardiac conditions and dysfunctions. [ABSTRACT FROM AUTHOR]

A geometrical model of the human heart is of interest in many fields of biophysics. The myocardium contains the electrical sources responsible for the generation of the body-surface ECG. An accurate geometric knowledge of these sources is crucial when dealing with the electrocardiographic forward and inverse problem. We developed a semiautomatic approach for segmenting the myocardium in order to deal with the electrocardiographic problem. The approach can be divided into two main steps. The first step extracts the atrial and ventricular blood masses by employing Active Appearance Models (AAM). The ventricular blood masses are segmented automatically after providing the positions of the apex cordis and the base of the heart. Due to the complex geometry of the atria the segmentation process of the atrial blood masses requires more information. We divided, therefore, the left and the right atrium into three divisions of appearance: the base of the heart, the lower pulmonary veins from its first up to the last appearance in the image stack, and the upper pulmonary veins. After successful extraction of the blood masses the second step involves morphologically-based operations in order to extract the myocardium either directly by detecting the myocardium in the volume block, or by reconstructing the myocardium using mean model information, in case the algorithm fails to detect the myocardium. [ABSTRACT FROM AUTHOR]

This paper describes a method for automatic contour detection in long-axis cardiac MRI using an adaptive virtual exploring robot. The robot is a simulated trained virtual autonomous tri-cycle that is initially positioned in a binary representation of the left ventricle (LV) and finds the contours during navigation through the ventricle. The method incorporates global and local prior shape knowledge of the LV in order to adapt the navigational parameters. Together with kinematic constraints, the robot is able to avoid concave regions such as papillary muscles and navigate through narrow corridors such as the apex. Validation was performed on in-vivo multiphase long-axis cardiac MRI images of 11 subjects. Results showed good correlation between the quantitative parameters, computed from manual and automatic segmentation: for end-diastolic volume (EDV) r=0.91, for end-systolic volume (ESV) r=0.93, ejection fraction (EF) r=0.77, and LV mass (LVM) r=0.80. [ABSTRACT FROM AUTHOR]

In this paper, a new technique (SPASM) based on a 3D-ASM is presented for automatic segmentation of cardiac MRI image data sets consisting of multiple planes with different orientations, and with large undersampled regions. SPASM was applied to sparsely sampled and radially oriented cardiac LV image data. Performance of SPASM has been compared to results from other methods reported in literature. The accuracy of SPASM is comparable to these other methods, but SPASM uses considerably less image data. [ABSTRACT FROM AUTHOR]

A novel approach to automated segmentation of X-ray Left Ventricu-lar (LV) angiograms is proposed, based on Active Appearance Models (AAMs) and dynamic programming (DP). Due to combined modeling of the end-diastolic (ED) and end-systolic (ES) phase, existing correlations in shape and texture representation are exploited, resulting in a better segmentation in the ES phase. The intrinsic over-constraining by the model is compensated by a DP algorithm, in which also cardiac contraction motion features are incorporated. An elaborate evaluation of the algorithm, based on 70 paired ED-ES images, shows success rates of 100% for ED and 99% for ES, with average border positioning errors of 0.68 mm and 1.45 mm respectively. Calculated volumes were accurate and unbiased, proving the high clinical potential of our method. [ABSTRACT FROM AUTHOR]

The relationships among vascular geometry, hemodynamics, and plaque development in coronary arteries are not yet well understood. This in-vivo study was based on the observation that plaque frequently develops at the inner curvature of a vessel, presumably due to a relatively lower wall shear stress. We have shown that circumferential plaque distribution depends on the vessel curvature in the majority of vessels. Consequently, we studied the correlation of plaque distribution and hemodynamics in a set of 48 vessel segments reconstructed by 3-D fusion of intravascular ultrasound and x-ray angiography. The inverse relationship between local wall shear stress and plaque thickness was significantly more pronounced (p<0.025) in vessel cross sections exhibiting compensatory enlargement (positive remodeling) without luminal narrowing than when the full spectrum of vessel stenosis severity was considered. Our findings confirmed that relatively lower wall shear stress is associated with increased plaque development. [ABSTRACT FROM AUTHOR]

Multi-slice computed tomography image series are a valuable source of information to extract shape and motion parameters of the heart. We present a method how to segment and label all main chambers (both ventricles and atria) and connected vessels (arteries and main vein trunks) from such images and to track their movement over the cardiac cycle. A framework is presented to construct a multi-surface triangular model enclosing all blood-filled cavities and the main myocardium as well as to adapt this model to unseen images, and to propagate it from phase to phase. While model construction still requires a reasonable amount of user interaction, adaptation is mostly automated, and propagation works fully automatically. The adaptation method by deformable surface models requires a set of landmarks to be manually located for one of the cardiac phases for model initialisation. [ABSTRACT FROM AUTHOR]