HK1237630B - Method of and apparatus for characterizing spatial-temporal dynamics of media excitable for deformation - Google Patents

Description

Method and device for characterizing the spatiotemporal dynamics of a medium that can be excited to deform

Technical Field

The present invention relates to a method for characterizing the spatiotemporal dynamics of a medium capable of being excited to deform. Furthermore, the present invention relates to a device for visualizing the spatiotemporal dynamics of a medium capable of being excited to deform. In particular, the medium capable of being excited to deform may be myocardium.

Cardiac arrhythmias, such as life-threatening ventricular fibrillation, are associated with rapid, highly irregular electrical activity that propagates in a wave-like manner through the heart and induces fibrillatory contractions of muscle tissue. The electrical and mechanical activity of the heart during fibrillation remains poorly understood because it is difficult to measure and visualize throughout the entire volume of the myocardium.

Background Art

US 2014/0276152 A1 discloses a system and method for identifying a drive mechanism associated with the source of a cardiac arrhythmia. The drive mechanism takes the form of a persistent rotational or centrifugal pattern associated with sensed cardiac electrical activity of a patient. To determine the source of the cardiac arrhythmia, data is evaluated from multiple sensors representing cardiac bioactivity. The sensors detect cardiac electrical information. These sensors can be inserted into the patient's heart or can detect cardiac electrical information via the patient's surface. US 2014/0276152 A1 notes that some sensors can also derive electrical cardiac information from non-electrical sensing devices such as echocardiography. However, US 2014/0276152 A1 does not provide details regarding the use of these sensors. Further information is provided only for sensors positioned adjacent to respective sensor locations or in contact with tissue in or near the heart under consideration. The detected cardiac electrical information is forwarded to a signal processing device configured to process the information to identify rotational electrical activity or centrifugal activity. Furthermore, a computing device identifies indications of persistent drive mechanism activity. A computing device displays an activation propagation map video that combines and spatially arranges data from multiple monophasic action potential voltages representing cardiac signals. Arrows indicate the rotational motion of the displayed information. Rotational activation is represented by phase singularities in the phase map. Phase singularities can be visualized as white dots in the video.

US 2014/0052118 A1 discloses a method and system capable of identifying ectopic foci, convolutions, or conduction pathways involved in re-entry arrhythmias within cardiac tissue. The system includes a medical device having one or more mapping elements and a programmable computer to identify ectopic foci and convolutions within cardiac tissue based, at least in part, on signals derived from a plurality of mapping elements at one or more tissue locations. The mapping elements are sensors or electrodes, such as monophasic action potential electrodes, capable of sensing electrical activity within cardiac myocytes as the cells polarize and depolarize.

US 2014/0200429 A1 discloses a method and system for mapping cardiac fibrillation in a patient. The method includes positioning a catheter in the patient's heart. The catheter includes an array of at least one stacked electrode pair comprising a first electrode and a second electrode. Each electrode pair is configured to be orthogonal to the surface of a cardiac tissue substrate. In response to electrical activity in the cardiac tissue substrate, a plurality of measurements are obtained from the electrode array, providing a continuous indication of a plurality of circuit cores in the patient's heart and the distribution of the circuit cores across the cardiac tissue substrate. Measurements are performed to obtain a density and distribution of the circuit cores mapped onto a representation of the patient's heart.

WO 2013/123549 A1 discloses a method for identifying a cardiac region for ablation to prevent or treat arrhythmias. The method includes determining one or more electrical waveform features of multiple cardiac locations, identifying a cardiac region with the largest variance of the one or more electrical waveform features, and identifying the cardiac region with the largest variance as the cardiac region for ablation. The determination of the electrical waveform features includes an electrocardiogram, in particular a bipolar electrocardiogram. The identification of the cardiac region with the largest variance includes generating a graph of the electrical waveform features. The cardiac region determined for ablation is a circumflex region, an endocardial/epicardial breakthrough region, a transmural reentry region, or a discontinuous propagation region.

US 2007/0049824 A1 discloses a system and method for detecting electromechanical wave propagation within a body structure of a patient in a series of image frames representing the movement of the body structure. Image data comprising a series of image frames corresponding to the movement of the body structure is acquired. Correlation calculations are performed on the image frames to generate a displacement map representing the relative displacement between the first and second image frames. A video comprising the series of displacement maps is generated. Motion parameters of the body structure are detected by analyzing the displacement map. Image acquisition can detect the movement of the body structure without causing the movement. In particular, the image data is acquired using an image detection device, such as an ultrasound probe, for generating images of the heart or other organs or structures of the patient. Thus, the known method uses elastography technology that can evaluate mechanical wave propagation to provide a non-invasive estimate of electrical propagation. Based on the observation that, in the context of certain diseased or affected tissues, electromechanical waves travel faster than in normal tissue, as observed through sequential images, the known method provides an imaging method for detecting such conditions, such as myocardial ischemia.

WO 2014/059170 A1 discloses a technique for mapping cardiac behavior including heart rhythm. A series of images of the heart are taken at one or more pixel positions. Each pixel position corresponds to a region of the heart. Image data corresponding to the pixel positions is obtained, and the periodicity of the image data measured for each pixel position on the series of images is measured. The periodicity corresponds to the electromechanical signals of the heart in the region corresponding to the measured one or more pixel positions. Through these techniques, a space-time map of the heart can be obtained, which shows the electromechanical patterns of atrial flutter, fibrillation and tachycardia in the heart. During focal arrhythmias such as ventricular contraction and focal atrial tachycardia, electromechanical wave imaging can be used to identify the location of the focal region and the subsequent propagation of cardiac activation. In known techniques, electromechanical wave imaging can be integrated into an ultrasound system to characterize the mechanical and electromechanical functions representative of atrial and ventricular arrhythmias. In addition, cardiac echocardiography can be used to provide real-time imaging of the heart to identify anatomical structures and guide ablation. Strain can also be assessed with high temporal resolution using intracardiac echocardiography together with myocardial elastography.

US 8,666,138 B2 discloses methods and systems for functional imaging of cardiac tissue based on the ability of imaging techniques to detect wave-induced tissue deformation at depth, allowing observation of the propagation of action potentials deep within myocardial tissue. The known methods and systems employ forward models, which describe the generation of displacements from known stresses, and inverse models, which describe the stresses that must exist to produce a given displacement field. In these models, the myocardium is considered to be an elastic, incompressible medium with what are believed to be known anisotropic properties.

US 2009/0219301 A1 discloses an ultrasound imaging system for evaluating and displaying deformation of a body organ. A sequence of image data sets comprising echo image data of at least a first image data set and a second image data set is acquired. A motion vector field is calculated between image points of the second image data set and image points of the first image data set. A reference point is selected within or outside the first and second image data sets. A first scan line is defined that includes the reference point. The motion vectors of the image points are projected onto the defined first scan line, and the motion vectors of the image points provide projected tissue velocities along the first scan line. The projected tissue velocities are used to estimate a component of the body organ deformation at the image point in the direction of the first scan line. This component of the body organ deformation, such as strain rate or strain, is further represented graphically in the sequence of image data sets. This known imaging system does not use an elastic model of the respective body organ that defines elastic interactions between elements of the body organ.

US 2013/0211256 A1 discloses a method for analyzing myocardial segment work based on strain and pressure measurements. The method is based on pressure measurement or estimation and strain measurement, preferably using echocardiography such as speckle tracking ultrasound imaging. Apparatus for receiving, preparing, and presenting data related to the work of individual myocardial segments from tissue strain imaging data includes a medical imaging device for non-invasively recording tissue strain imaging data for two or more myocardial segments; and an electronic processor capable of calculating mechanical power and mechanical work traces for the two or more individual myocardial segments as a function of time for a time period including the interval from the start of an isovolumetric contraction phase to the end of an isovolumetric relaxation phase, from a ventricular tissue strain trace for each of the two or more myocardial segments and a non-invasively determined pressure trace proportional to the ventricular pressure and time-synchronized with the strain trace. This known method does not use an elastic model of the respective myocardium that defines elastic interactions between myocardial elements.

Purpose of the Invention

The object of the present invention is to provide a method for characterizing the spatio-temporal dynamics of a medium that can be excited to deform, and an apparatus for visualizing the spatio-temporal dynamics of a medium that can be excited to deform, which allow the mechanical activity of the medium to be non-invasively imaged in a manner that reflects the temporal development of the electrical activity that excites the medium for deformation.

Solution

The problem of the invention is solved by a method comprising the features of independent claim 1 and by a device comprising the features of independent claim 18. The dependent claims relate to preferred further developments of the method and device according to the invention.

Summary of the Invention

In a method for characterizing the spatio-temporal dynamics of a medium that can be excited to deform, the medium is imaged at successive points in time to obtain a series of images. Here, the term "image" refers to two-dimensional or three-dimensional image data representing a projection, cross-section, or volume of the medium, or a sparse, arbitrarily sampled representation of the medium. The image data can display the medium in a rasterized manner along a regular array of uniformly distributed locations, or at sparse and arbitrarily distributed locations throughout the medium, or in other manners specific to the operating mode of the imaging mode used. Thus, the image data can include pixels or voxels or any other geometric or volumetric subunits in a structured or unstructured grid organization. In addition to Cartesian coordinate systems, as in the case of 3D echocardiography with a sector transducer, images can be obtained in polar coordinate systems or spherical coordinate systems. The term "image" also covers a set of two-dimensional images, in particular a set of two-dimensional images of the medium imaged along a set of parallel imaging planes.

Images of the medium are used to determine the displacement of the medium's structure between the series of images. The structure of the medium whose displacement is determined is any structure identifiable in the image. Accordingly, the structure of the medium evaluated will depend on the imaging technique used. A dynamic description of the temporal evolution of the spatial deformation of a predefined elastic model of the medium is adapted to the determined displacement of the medium's structure.

Elastic models can involve mathematical and computational descriptions of elastic continua that undergo affine or non-affine deformations that may be finite and have mechanical constitutive laws for the continuum, configured or adapted for the specific material properties of the medium. For example, in a discrete description of the medium, the model can consist of a set of particles occupying a space or volume that defines the medium, and this set of particles can retain specific particle interactions that introduce elastic or soft tissue-like behavior and support vibrations and waves throughout the medium as the particle system dynamically seeks a specific stress equilibrium. In addition, the interaction scheme can allow for the introduction of preferred orientations and other elastic behaviors that may be non-linear and specific to the medium. For example, continuous computational and viscoelastic descriptions can also be used to model the elasticity of the medium. Elastic models can also involve mathematical and computational descriptions of internal processes that occur and result in deformation of the medium that can be excited to deform. For example, an elastic model can consider that strain waves caused by electrical action potential waves will not be reflected like standard elastic waves, but will also contain components of internal active stresses.

An elastic model is predefined to describe the elasticity of a medium. The dynamic description of the temporal evolution of the spatial deformation of the elastic model can also be referred to as the dynamic model of the medium. The dynamic description or model is adapted to match the displacements of a determined structure. From the dynamic description or model, the temporal evolution of the rate of deformation pattern in the medium is identified. Here, the rate of deformation generally refers to a dynamic continuum mechanical measure of deformation, i.e., the rate of deformation at a local material element of the continuum, i.e., the strain rate or strain rate acceleration. For example, these kinematic measures can be derived and used directly based on the rate of the deformation tensor or strain rate tensor, or obtained by further analysis as the derivative of the deformation tensor with respect to time. Furthermore, using invariants or eigenvalue decompositions of tensors such as principal strains and stretches or similar kinematic quantities and their behavior over time, tensor-valued measures of deformation and rate of deformation can be converted into vector or scalar measures of deformation or rate of deformation, respectively.

The inventors could show that the method of the present invention is able to resolve, for example, spatially and temporally, the activity of mechanical vortex gyres that occur in myocardium affected by ventricular fibrillation. The inventors could also show that these mechanical vortex gyres are strongly correlated with the electrical action potential vortex wave activity involved in ventricular fibrillation. The correlation between the mechanical vortex gyres and the electrical action potential vortex wave gyres is so strong that the method according to the present invention can be used to image the electrical action potential by means of the rate at which the deformation pattern of the medium is caused. However, even if it is not intended to image electrical activity, imaging the mechanical activity according to the present invention will provide a valuable tool for characterizing the dynamic activity and state of the medium.

In particular, the method of the present invention allows the identification of centers of rotation from a dynamic description or model. These centers of rotation are those points in the medium at which the rate of the deformation pattern of the medium rotates. Rotating electrical action potential wave patterns are associated with electrical spiral and vortex wave activity, which is believed to be the pattern-forming, self-organizing mechanism underlying cardiac fibrillation. Spiral and vortex wave convolutions are dynamically formed around the center of rotation, which can be depicted in three dimensions by two phase singularities and phase singularity lines, respectively. Rotating electrical activity interacts with the heterogeneous cardiac substrate. Specifically, the rotating core regions of the vortex waves are believed to be anchored to anatomical obstacles or heterogeneities within the myocardium. At the same time, the obstacles and heterogeneities themselves can be activated as sources of electrical activity and can be used to control and terminate fibrillation using low-energy anti-fibrillation pacing techniques. Therefore, the development of therapeutic strategies to successfully terminate or control cardiac fibrillation relies on detailed knowledge of the organization of the underlying electrical patterns, for example, more specifically, on the location and alignment of the rotating core regions of the rotating structures of the turbulent electrical wave patterns within the myocardium. Therefore, identifying the centers of rotation according to the invention is of particular value since the inventors have shown that these centers of rotation identified from the dynamic description or model coincide with the centers of rotation of the individual action potentials that lead to deformations of a medium such as the myocardium.

However, the method of the present invention is not limited to the identification of the center of rotation. The method of the present invention can also be used to identify other activity patterns such as focal or centrifugal activity patterns. To this end, the rate of the deformation pattern identified from the dynamic description or model can be converted into an electrical activity (i.e., action potential, calcium transient) pattern using another electrical model of the corresponding medium, which is coupled to the elastic model so that the two models together constitute an electromechanical model. Alternatively, the elastic model can also cover the special electromechanical properties of the medium, i.e., the correlation between the electrical action potential or calcium transient of the medium and the mechanical deformation, including any inhomogeneity of the correlation.

Incorporating an electrical model into the method according to the present invention can enhance the imaging process because the electrical model can impose constraints on possible solutions for the elastic model's adaptability to the measured deformation of the imaged tissue volume. These constraints correspond to imposing dynamic boundary conditions, temporal sequences, or dependencies on the elastic model's adaptation process. For example, in the heart, specific behaviors of electrical activity, such as the directionality of wave propagation that produces characteristic wave phenomena and the disappearance of waves at dielectric boundaries, lead to specific muscle deformations. These deformations can be forced by the adaptation of the elastic model, rather than by other, non-physical, or atypical types of deformation, and these deformations can evolve over time. In particular, the electrical model, combined with a mechanism that initiates electrical activity in the electrical model according to a certain rule and based on events measured or observed in the elastic model, can generate electrical wave patterns that are separate from, but evolve in accordance with, the elastic activity. Because electrical activity in the electrical model can be coupled to initial contractile forces or deformations also in the elastic model, the electrical activity can influence the elastic model's adaptability to the measured tissue volume's deformation, and this can be done, for example, in an iterative process. As an example, the dynamic events occurring in the elastic model can cause the corresponding elements or components in the electrical model to be excited and trigger the propagation of electrical activity waves in the electrical model. These wave patterns of electrical activity can be visualized like this, or these wave patterns can be used for example to trigger the contraction or deformation of the corresponding elements or components in the elastic model. Therefore, the adaptation of the elastic model to the deformation of the measured tissue body will include the active internal stress component that causes deformation. And, according to the coupling desired, other coupling mechanisms can be implemented in the coupling between the electrical and elastic models. For example, the electrical model can include a mechanism that induces electrical excitation when the corresponding elements or components of the elastic model undergo mechanical stretching.

In one embodiment of the method according to the invention, the rate of the deformation pattern identified from the dynamic description or model is displayed as a phase diagram or phase representation. In such a phase diagram, the position of the mechanical wavefront is depicted, for example, by different colors at different phases. The shape of the wavefront and its route through the medium can be obtained from these phase diagrams. Thus, for example, the phase diagram allows to see which parts of the medium are affected by which local anatomical activity pattern and by which mechanical gyrus. Any center of rotation can be displayed in the phase diagram as a phase singularity or a phase singularity line. Similarly, the calculated electrical pattern derived from the electrical model can be displayed as a phase diagram or phase representation.

The imaging technique used in the method of the present invention for imaging a medium at successive time points can be, for example, ultrasound imaging, particularly two-dimensional or three-dimensional brightness mode ultrasound imaging, magnetic resonance imaging, but can also be optical imaging techniques such as optical coherence tomography, light sheet imaging, or microscopy. The structure of the medium depicted by ultrasound imaging will include a structure defined by the elastic and acoustic reflection properties of the medium. Because the elasticity of a deformable medium is affected by the strain of the medium, the depicted structure includes direct information about the strain and strain rate distribution in the medium.

In practice, the displacement of the structure of the medium can be determined using correlation-based speckle tracking techniques or other image registration and motion tracking techniques. These techniques are well known and can be automatically and rapidly implemented to perform the entire method according to the present invention in real time or near real time. Other information directly available from the imaging modality regarding the possible displacement of the medium can also be used.

The selection of parameters for the elastic and electrical models can be made before or during the imaging process, as appropriate, since the parameters can be identified during imaging based on the dynamic behavior modeled from data-driven analysis. Alternatively, the parameters can be set based on the behavior of the ab electrocardiogram, which may be available at any time during the imaging process.

In the method according to the present invention, the elastic model of the medium and the dynamic description of the temporal evolution of the spatial deformation of the elastic model fill in the gaps between the traced patterns or structures. Even with a relatively low level of detail in the elastic model definition and a relatively low level of adaptation of the elastic model to the actual medium, the dynamic description of the elastic model and the temporal evolution of the spatial deformation of the elastic model allows for monitoring strain rate patterns of interest. However, adapting the elastic model to the actual elastic properties of the medium, based on the dynamic description, enhances the accuracy, i.e., the spatial and temporal resolution, when imaging the rates of deformation patterns in the medium. For example, if the propagation of mechanical wavefronts in the medium is much faster in one direction than in another, or if the rates of the deformation pattern exhibit strong spatial gradients or other dynamic features or specific behavior along a preferred orientation, this may indicate that the medium is not isotropic but rather has a fibrous structure with fibers extending along the direction of fastest propagation. In this way, for example, the orientation of myocardial muscle fibers can be determined and implemented in an elastic model of the myocardium. In addition to anisotropy, contractile and elastic heterogeneity can be assessed and incorporated into the model. Furthermore, for example, if a dynamic description or model is used to measure the rate of deformation and this information is found to provide an estimate of the distribution of underlying processes within the medium responsible for the deformation, such as electrical excitation or contractile activity, adapting the dynamic model to include this information may help improve the accuracy of the model. For example, such an estimate can be obtained by analyzing the dynamic characteristics of the model's spatial and temporal evolution. Alternatively, such an estimate can be obtained by modeling the internal processes described above and synchronizing or converging the two parts of the model through an iterative and dynamic process.

As described above, centers of rotation or focal activity identified from a dynamic description or model can be directed in treatments directly targeting the formation of spiral or vortex wave convolutions similar to those that occur during ventricular fibrillation or targeting other re-entry and arrhythmic cardiac activity. More specifically, one or more centers of rotation or focal activity can be selected as a set of reference points based on the method according to the present invention to identify suitable ablation targets. In addition, possible abnormalities, heterogeneous contractile activity or elastic behavior that can be identified using a dynamic description or model can be associated with fibrotic structures and used to identify locations for ablation or other forms of treatment. In addition, the ablation device used to remove these ablation targets can be guided by the same imaging technology used to image the medium.

Furthermore, based on the methods according to the present invention, one or more centers of rotation or focal activity can be selected as a set of reference points to identify suitable pacing targets. Furthermore, the pacing device used to pace these pacing targets can be guided by the same imaging technology used to image the medium. One or more centers of rotation or focal activity can be used to visualize and analyze the local anatomical structure of cardiac activity. That is, in two spatial dimensions, such as in the case of a thin, extensible, deformable medium, the local anatomical structure can be depicted by the number, density distribution, creation and disappearance rates, and motility behavior of phase singularities, as well as a phase map of the activity around the phase singularities over time. In three spatial dimensions, such as in the case of a bulky, excitable, deformable medium, the local anatomical structure can be depicted by the number, alignment, length, density, creation and disappearance rates of phase singularity lines, as well as a phase map of the activity around the phase singularity lines over time. In particular, the dynamics of activity and the dynamic characteristics and statistical properties of the local anatomical structure, such as the frequency distribution or degree of synchronization of periodic activity, can be used to characterize and distinguish different pathophysiological stages and forms of activity. For example, it can be used to characterize and differentiate between different variants of atrial flutter or tachycardia or atrial or ventricular fibrillation, or to locate the source of arrhythmic activity or other critical areas within the media that contribute to a certain disease state. Knowledge of the organization of activity, i.e., the local anatomy, can be used to develop long-term interventional strategies for treating or preventing arrhythmias, but can also be used to develop technologies for immediate intervention in arrhythmic activity, and can be used for treatment planning, targeting, and assessment, as well as for in vitro drug screening of drugs, compounds, compositions, and other products.

As an example, in conjunction with pacing techniques employing, for example, electrical or optical stimulation or ultrasound-related stimulation at sub-ablative energies, the visualization and analysis of activity described above can be used to enable interaction with the activity during the imaging process to alter the intrinsic structural organization of the activity by applying corresponding timed stimulation at locations specifically selected based on information provided by the analyzed imaging. This interaction can, in a therapeutic setting, shift the activity away from a long-term pathophysiological state or, in an emergency, terminate unstable arrhythmic activity.

As another example, in the case of applying an ablation procedure, the effectiveness of the application can be monitored or controlled and evaluated during and after the procedure. During and after the procedure, changes in activity can be observed and evaluated within the local ablation area or within a larger portion of the medium or the entire medium, given that the ablation can be observed to affect the entire activity pattern via the imaging process. In addition, the steps of imaging the medium, determining the displacement of the structure, adapting the dynamic description and identifying the time development of the rate of deformation pattern can be performed before and during and/or after the drug to be tested is administered to the medium; and these steps can be repeated for each of a plurality of drugs. The time development of the rate of deformation pattern identified for each of the plurality of drugs can then be compared to each other to select potential antiarrhythmic drugs from the plurality of drugs. These embodiments of the method of the present invention can be performed in vivo at the myocardium of a living individual or in vitro at a test medium that can also be myocardium.

An apparatus for visualizing the spatiotemporal dynamics of a medium capable of being induced to deform, according to the present invention, includes an imaging system configured to image the medium at successive points in time to obtain a series of images. In particular, the imaging system may be an ultrasound imaging system. The apparatus also includes an evaluation system configured to implement the method of the present invention for identifying the rate of a deformation pattern in the medium, and a visualization system configured to display the rate of the deformation pattern in the medium. The visualization system may, for example, display a phase diagram of the rate of the deformation pattern and local anatomical defects such as phase singularities and phase singularity lines.

The apparatus according to the present invention may also include an ablation device, in particular an ablation device configured to be guided by an imaging system. The ablation device may, for example, include a catheter or a non-catheter-based device for directing ablation energy to the ablation target. The ablation device may further be, for example, based on high-intensity focused ultrasound and combined with, or used in combination with, an ultrasound device for imaging the ablation procedure. The ablation energy may be, for example, electrical, RF, or light energy, or acoustic energy related to ultrasound.

Apparatus according to the present invention may also include a pacing device, particularly a pacing device configured to be guided by an imaging system. The pacing device may apply stimulation to the medium at various spatial locations in a well-defined, timed manner based on information provided by the imaging system. The stimulation may be provided, for example, by electrodes or optical probes that provide electrical or optical stimulation, respectively. The stimulation may also include ultrasonic acoustic stimulation using focused ultrasound at energies below ablative energy.

Advantageous developments of the invention result from the claims, the description and the drawings. The advantages of the features and combinations of features mentioned at the beginning of the description serve only as examples and may be used alternatively or cumulatively without necessarily achieving these advantages according to the embodiment of the invention. Without changing the scope of protection defined by the appended claims, the following applies to the disclosure of the original application and patent: Further features can be taken from the drawings, in particular from the illustrated design and dimensions of the components relative to one another and from the relative arrangement of the components and their operational connections. Combinations of features of different embodiments of the invention or of features of different claims are possible and therefore also motivated independently of the reference to the selected claims. This also relates to features that are shown in individual drawings or mentioned when describing them. These features can also be combined with features of different claims. Furthermore, other embodiments of the invention may not have the features mentioned in the claims.

Reference to a number of features in the claims and the specification should be understood to cover the exact number and any greater number than that recited, without the explicit use of the adverb "at least." For example, if reference is made to a picture, it should be understood that there may be only one picture, or two or more pictures. Additional features may be added to these features, or these features may be the sole features of the respective product.

Reference signs included in the claims do not limit the scope of the matter protected by the claims. Their only function is to make the claims easier to understand.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention is further illustrated and described with respect to preferred exemplary embodiments shown in the drawings.

FIG1 is a block diagram of an embodiment of the method and apparatus of the present invention.

FIG2 shows an apparatus to which one embodiment of the present invention is applied.

FIG3 compares the electrical action potentials (a) and mechanical activity (b) determined for both experiments according to the experimental setup of FIG2 .

FIG4 shows another apparatus for applying another embodiment of the present invention.

Figures 5(a)-(c) illustrate possible approaches to adapting the elastic model to dynamically track deformation; and

Figures 6(a)-(d) illustrate the steps of a method according to the invention, which comprises a final step of transforming the rate of deformation pattern into an electrical action potential pattern using an electromechanical model of the corresponding medium.

DETAILED DESCRIPTION

FIG1 illustrates the various steps of an embodiment of a method for characterizing the spatiotemporal dynamics of an excitable deformable medium according to the present invention. FIG1 also illustrates the basic components of an apparatus for visualizing the spatiotemporal dynamics of an excitable deformable medium according to the present invention. An excitable deformable medium 1 is imaged by an ultrasonic imaging device 2 for obtaining a series of images of the medium 1. In an evaluation system 3, the images are analyzed for shifts in the structure of the medium between the images. This analysis is based on a correlation-based speckle tracking method, i.e., correlations between consecutive images are evaluated for shifts in speckle patterns as an indication of shifts in the structure of the medium associated with the speckle patterns. The determined shifts are used to adapt the dynamic description of the temporal evolution of the spatial deformation of a predefined elastic model. Adaptation is not performed until the dynamic description of the temporal evolution of the spatial deformation of the elastic model of the medium describes the shifts in the determined structure. The dynamic description of the temporal evolution of the spatial deformation of the elastic model can also be referred to as a dynamic model of the medium 1. From this dynamic model, the temporal evolution of strain rate patterns in the medium 1 is identified. These strain rate patterns reflect the distribution and temporal evolution of mechanical activity in the medium 1.

A visualization system 4, such as a monitor, can be used to visualize the identified strain rate pattern, in particular the rotational strain rate pattern, together with the center of rotation of the strain rate pattern. The visualization system 4 can also be used, based on information about at least one or more visualized centers of rotation, to guide an ablation device 5 for partially ablating the medium 1 and/or a pacing device for applying stimulation at a location within the medium 1. By ablating or pacing the medium 1, the cause of the rotational strain rate pattern can be removed. This technique can be used, for example, to remove the cause of ventricular fibrillation in the myocardium. This is possible because the mechanical activity visualized according to FIG1 is closely related to the electrical action potential in the myocardium.

FIG2 depicts a setup that has been used to demonstrate the correlation between mechanical activity and electrical action potential activity on the epicardial surface and within the left ventricular wall of a Langendorff-perfused rabbit heart 6 during ventricular fibrillation. In heart 6, LV denotes left ventricle, RV denotes right ventricle, and RA denotes right atrium. Mechanical activity was monitored using an ultrasound imaging device 2 operating in B-mode and providing images at 300 frames per second, as in FIG1 . Electrical action potentials were monitored by fluorescence imaging using a fluorescent probe sensitive to the transmembrane potential and Ca2+ concentration at the surface of heart 6. The fluorescent probe was excited by fluorescent light from a light source 7, and the fluorescent light was directed to a camera 8 at 500 frames per second.

FIG3(a) shows a phase diagram of the electrical action potential on the surface of the heart 6 according to FIG2 when the electric vortex wave rotates around the rotation center 9 as shown by arrow 10. FIG3(b) shows the resulting mechanical vortex wave, that is, a phase diagram of the strain rate pattern at the same surface as in FIG3(a), rotating around the same rotation center 9 with a very similar shape of the wavefront. The direction of rotation, also shown by arrow 10, is the same as that in FIG3(a), that is, clockwise, and the frequency of rotation is also the same. Therefore, the rotation center of the mechanical vortex wave according to FIG3(b), identified by the ultrasonic imaging device 2 according to FIG2, points to the rotation center 9 of the electric vortex wave according to FIG3(a). Therefore, the non-invasive ultrasonic imaging device 2 can be used to identify potential ablation targets in the treatment of ventricular fibrillation, showing the electric vortex wave according to FIG3(a).

FIG4 depicts another apparatus for implementing an embodiment of the present invention and a heart 6. The heart 6 may be the heart of a living individual or an in vitro heart preparation. The mechanical activity of the myocardium of the heart 6 is monitored using an ultrasound imaging device 2 that provides three-dimensional images of the heart 6. These three-dimensional images allow the mechanical activity to be spatially resolved in all three spatial dimensions. In FIG4 , vortices 11 propagating in the myocardium of the heart 6 are represented. Furthermore, in addition to the representation in FIG2 , LA represents the position of the left atrium of the heart 6. FIG4 also shows that images taken using the ultrasound imaging device 2 can be used to guide an ablation device 5 within the heart and/or a pacemaker device 12 relative to the heart. By using an apparatus for simultaneously monitoring the mechanical activity of the myocardium using the ultrasound imaging device 2, the effects of any ablation performed with the aid of the ablation device 5 and/or any pacing performed with the aid of the pacemaker device 12 will be seen and can be evaluated in real time.

Figure 5(a) depicts how, in the next time step, each element of the medium is accelerated along the acceleration vector a toward the assumed tracking position of the medium element x(t+1)=x(t)+u(t). The passive elastic force of the elastic model of the medium acting on the medium element x represented by the spring causes a displacement u that deviates from the direct displacement in the direction of the vector a.

Figure 5(b) shows the iterative adaptation of the dynamic description of the elastic model to the tracked displacement field using the continuous acceleration of the dielectric particles and the equilibrium of the configuration of the dielectric elements. A single dielectric element moves along a trajectory given by u.

Figure 5(c) shows a possible final solution of the adaptation of the dynamic description of the elastic model based on an approximation of the original displacements. The final position of the dielectric element is the spatial average of the original displacements and the final position of the particles in the elastic model.

FIG6( a ) illustrates the determination of the shift of the structure of each medium between two images of the medium.

FIG6( b ) depicts a dynamic description of the temporal evolution of the spatial deformation of the elastic model of the adapting medium to match the displacement of the structure.

FIG6( c ) depicts the temporal development of the rate at which deformation patterns in the medium showing as mechanical vortex waves are identified from the dynamic description.

Figure 6(d) shows the transformation of the rate of deformation pattern into an electrical action potential pattern shown as an electrical vortex wave using an additional electro-mechanical model of the medium. Furthermore, iterative adaptation of the electromechanical model and the elastic model is shown in Figures 6(c) and (d).

Reference Signs List

1 Medium

2 Ultrasound imaging device

3 Evaluation System

4 Visualization System

5 Ablation devices

6 Heart

7 Light Source

8 cameras

9 Center of rotation

10 arrows

11 Vortex Wave

12 Pacemaker

Claims (23)

1. A method for characterizing the spatial-temporal dynamics of a deformable medium (1), the method comprising: Define the elastic model of medium (1); Imaging of the medium (1) at consecutive time points to obtain a series of images; Determine the structural displacement of the medium (1) between a series of images; and Its features Adapting the dynamic description of the temporal evolution of spatial deformation in the elastic model to match the displacement of the structure; and Identify the temporal evolution of the rate of deformation patterns in medium (1) from dynamic description. The method further includes: Imaging the electrical activity of a medium by means of the rate of deformation patterns, The rate of deformation pattern in medium (1) corresponds to the pattern of strain rate or strain rate acceleration in the medium. 2. The method as claimed in claim 1, characterized in that the rate of the deformation pattern is converted into an electrical activity pattern by: Define the electrical model of medium (1); Couple the elastic model of dielectric (1) to the electrical model of dielectric (1); and The time evolution of the electrical activity of the electrical model of medium (1) is adapted to the time evolution of the deformation pattern rate in the coupled elastic model of medium (1). Among them, the electrical activity pattern corresponds to the action potential pattern or the calcium transient pattern. 3. The method as described in claim 2, characterized in that the rotation center is identified from the time evolution of the electrical activity, and the electrical activity pattern rotates in the medium (1) around the rotation center. 4. The method as claimed in claim 3, wherein the electrical activity pattern in the medium (1) is displayed as a phase diagram. 5. The method according to any one of claims 1-4, characterized in that the rotation center is identified from the dynamic description, and the rate of rotation of the deformed pattern around the rotation center is in the medium (1). 6. The method as claimed in claim 5, wherein the rate of deformation pattern in medium (1) is displayed as a phase diagram. 7. The method as described in claim 4, wherein the rotation center is displayed as a phase singularity or a phase singularity line in the phase diagram. 8. The method as claimed in claim 6, wherein the rotation center is displayed as a phase singularity or a phase singularity line in the phase diagram. 9. The method according to any one of claims 1-4, 7, characterized in that the medium (1) is imaged by at least one of the following: Ultrasound imaging, Magnetic resonance imaging, Optical imaging and Microscopic examination. 10. The method according to any one of claims 1-4, 7, characterized in that the displacement of the structure of the medium (1) is determined using at least one of the following: Image registration, Motion tracking Space-related and Based on relevant pattern tracking. 11. The method according to any one of claims 1-4 and 7, wherein the elastic model is adapted based on a dynamic description of the elastic properties of the medium (1). 12. The method according to any one of claims 1-4 and 7, wherein the medium is myocardium. 13. The method as claimed in claim 3, wherein at least one of the rotation centers (9) is selected as a reference point for identifying the ablation target or pacing target. 14. The method as claimed in claim 5, wherein at least one of the rotation centers (9) is selected as a reference point for identifying the ablation target or pacing target. 15. The method according to any one of claims 1-4, 7, and 13, characterized in that at least one of the ablation device (5) and the pacemaker is guided by means of the step of imaging the medium (1). The method is performed in a medium held in vitro. 16. The method according to any one of claims 1-4, 7, and 13, characterized in that the steps of imaging the medium, determining the displacement of the structure, adapting the dynamic description, and identifying the rate of temporal evolution of the deformation pattern are performed before, during, and/or after the application of the drug to be tested to the medium (1). The method is performed in a medium held in vitro. 17. The method of claim 16, characterized in that the steps of imaging the medium, determining the displacement of the structure, adapting the dynamic description and identifying the rate of deformation pattern are performed before, during and/or after the drug to be tested is applied to the medium (1) for each of a plurality of drugs, and the time development of the rate of deformation pattern identified for each of the plurality of drugs is compared with each other to select potential antiarrhythmic drugs from the plurality of drugs. 18. The method of claim 9, wherein the optical imaging comprises optical coherence tomography. 19. An apparatus for visualizing the spatial-temporal dynamics of a medium (1) capable of being excited to deform, the apparatus comprising: An imaging system configured to image a medium at consecutive time points to obtain a series of images; Evaluation system (2), configured to determine the structural displacement of the medium (1) between a series of images; and Visualization system (4); Its features The evaluation system (2) is configured to implement the method of any one of the preceding claims for identifying the rate of deformation patterns in the medium (1) or respectively deriving corresponding electrical activity patterns in the medium (1); and The visualization system (4) is configured to display the rate or electrical activity pattern of the deformation pattern in the medium (1). 20. The device as claimed in claim 19, characterized in that... The evaluation system (2) is configured to implement the method as described in any one of claims 1 to 18 for identifying an electrical activity pattern in the medium (1); and The visualization system (4) is configured to display an electrical activity pattern in the medium (1). 21. The device as claimed in claim 19 or 20, wherein the imaging system comprises at least one of the following: Ultrasonic imaging device (2), Magnetic resonance imaging device Optical coherence tomography apparatus, Camera and Optical microscope. 22. The device of claim 19 or 20, further comprising at least one of an ablation device (5) configured to be guided by an imaging system and a pacing stimulation device. 23. The device of claim 21, further comprising at least one of an ablation device (5) configured to be guided by an imaging system and a pacing stimulation device.