阅读说明：本技术 用于在从估计的心脏射血输出导出的患者特异性边界条件下模拟血流量的方法和装置 (Method and apparatus for simulating blood flow under patient-specific boundary conditions derived from estimated cardiac ejection output ) 是由 J·彼得斯 J·威斯 H·施米特 于 2013-12-12 设计创作，主要内容包括：本发明涉及一种用于在根据每次心搏的心脏射血输出导出的患者特异性边界条件下模拟通过心血管结构的血流量的方法和装置,所述心血管结构例如为血液腔,例如,左心室流出道、包括AV的主动脉根部以及升主动脉、心室体积、主动脉或血液流过的任何其他空腔。可以根据在两个或更多个不同时间点上的不同充盈状态下的患者心腔的体积来估计心脏射血输出。流量模拟的结果可用于导出至少一个生理参数或者可以进行可视化,并且可以生成虚拟多普勒超声图像,以允许医生评估所述结果。(The present invention relates to a method and apparatus for simulating blood flow through a cardiovascular structure, such as a blood cavity, e.g. the left ventricular outflow tract, the aortic root including AV, and the ascending aorta, the ventricular volume, the aorta or any other cavity through which blood flows, under patient-specific boundary conditions derived from the cardiac ejection output per heart beat. The cardiac ejection output may be estimated from the volume of the patient's heart cavity at different filling states at two or more different points in time. The results of the flow simulation may be used to derive at least one physiological parameter or may be visualized and virtual doppler ultrasound images may be generated to allow the physician to evaluate the results.)

1. An apparatus for simulating blood flow through a cardiovascular structure proximate a heart of a patient, the cardiovascular structure including a left ventricular outflow tract, an aortic root including an Aortic Valve (AV), and an ascending aorta, the apparatus comprising:

an estimation circuit (40) for estimating a cardiac ejection output per heart beat based on the volume of the Left Ventricle (LV) of the patient at two or more points in time in different filling states, and for deriving from the cardiac ejection output per heart beat at least one patient-specific boundary condition for the blood flow through the cardiovascular structure;

a modeling circuit (12) for generating a volumetric mesh of the cardiovascular structure based on a segmented digital image of the cardiovascular structure; and

a simulation circuit (50) for simulating a blood flow through the volume mesh of the cardiovascular structure under consideration of the patient-specific boundary conditions to visualize the blood flow or to derive at least one physiological parameter of the patient, wherein the volume mesh represents the cardiovascular structure for an open valve state of the Aortic Valve (AV).

2. The apparatus of claim 1, wherein the digital image is a computed tomography image or a magnetic resonance image or an ultrasound image.

3. The apparatus according to claim 1, wherein the apparatus is adapted to derive from the simulated blood flow one or more of the following in the cardiovascular structure: pressure drop, mean blood residence time, flow rate, wall shear stress, and blood swirl.

4. A method of simulating blood flow through a cardiovascular structure proximate a heart of a patient, the cardiovascular structure including a left ventricular outflow tract, an aortic root including an Aortic Valve (AV), and an ascending aorta, the method comprising:

estimating a cardiac ejection output per heart beat based on the volume of the Left Ventricle (LV) in different filling states of the patient at two or more points in time;

deriving at least one patient-specific boundary condition for the blood flow through the cardiovascular structure from the cardiac ejection output per heart beat;

partitioning the digital image by using model-based segmentation to obtain a surface mesh of the cardiovascular structure;

obtaining a volumetric mesh of the cardiovascular structure by transforming or transforming the surface mesh; and is

Simulating blood flow through the volume mesh of the cardiovascular structure under consideration of the patient-specific boundary conditions to visualize the blood flow or to derive at least one physiological parameter of the patient, wherein the volume mesh represents the cardiovascular structure for an open valve state of the Aortic Valve (AV).

5. The method of claim 4, wherein the simulation is a computational fluid dynamics simulation or a fluid-solid interaction simulation.

6. The method of claim 4, further comprising estimating the cardiac ejection output for each heart beat based on an electrocardiographically gated digital image.

7. The method according to claim 4, further comprising estimating the cardiac ejection output per heart beat based on digital images of the Left Ventricle (LV) in a maximum filling state and a minimum filling state.

8. The method of claim 4, further comprising using the estimated cardiac ejection output per heart beat to define blood flow from the left ventricular outflow tract to the cardiovascular structure.

9. The method of claim 8, further comprising deriving the at least one patient-specific boundary condition by estimating a flow distribution over the left ventricular outflow tract and its temporal behavior.

10. The method of claim 9, further comprising estimating the flow distribution by defining a quadratic or velocity distribution of pulsating flow.

11. The method of claim 4, further comprising: estimating the cardiac ejection output per heart beat based on the volume of the Left Ventricle (LV) of the patient at the end of systole and at the end of diastole.

12. The method of claim 4, further comprising generating virtual Doppler ultrasound images based on the simulated blood flow.

13. An apparatus to simulate blood flow through a cardiovascular structure proximate a heart of a patient, the cardiovascular structure including a left ventricular outflow tract, an aortic root including an Aortic Valve (AV), and an ascending aorta, the apparatus comprising:

means for estimating a cardiac ejection output per heart beat based on the volume of the Left Ventricle (LV) at two or more points in time that the patient is in different filling states;

means for deriving at least one patient-specific boundary condition for the blood flow through the cardiovascular structure from the cardiac ejection output per heart beat;

means for obtaining a surface mesh of the cardiovascular structure by partitioning the digital image using model-based segmentation;

means for obtaining a volumetric mesh of the cardiovascular structure by transforming or transforming the surface mesh; and

means for simulating blood flow through the volume mesh of the cardiovascular structure to visualize the blood flow or to derive at least one physiological parameter of the patient under consideration of the patient-specific boundary conditions, wherein the volume mesh represents the cardiovascular structure for an open valve state of the Aortic Valve (AV).

Technical Field

The present invention relates to the field of simulating blood flow through a target cardiovascular structure, such as, but not limited to, the left ventricular outflow tract, the aortic root including the Aortic Valve (AV), and the patient-specific geometry of the ascending aorta, based on information acquired by medical imaging techniques.

Background

Degenerative Aortic Stenosis (AS) is the second most common cardiovascular disease in Western Europe and North America older than 65 With an incidence of 2-7%, AS described in "Multislice calculated cardiovascular for Detection of Patents With oral Valve Stenosis and Quantification of sensitivity" (Journal of the American College of medicine 2006, 47(7), p. 1410-1417) by G.M.Feuchtner, W.Dichtl et al.

Treatment of patients with degenerative AS depends on the severity of the disease. The assessment of the severity of Aortic Valve (AV) stenosis may involve different imaging modalities. Current assessments of severity are primarily based on ultrasound and doppler measurements of the AV region or on geometry measurements derived from Magnetic Resonance Imaging (MRI) or Computed Tomography (CT) images of the AV region.

For about 60-70% of patients, ultrasound can be used to image the valve and measure blood flow velocity via doppler measurements. For stenotic valves, the blood must flow at a higher velocity due to the reduced effective opening area, and the doppler measurement can be used AS an indicator of aortic valve stenosis (AS).

Using Electrocardiographic (ECG) gating, CT and MRI allow images to be reconstructed or acquired according to selected stenotic cardiac cycle intervals and provide images showing the valve in a relatively short open state. Feuchtner, W.Dichtl et al at "Multislice Computed Tomography for Detection of Patients With atomic Valve and Quantification of Severity" (Journal of the American College of medicine 2006, 47(7), p. 1410 1417), and Y.Westermann, A.Geigenemuller et al at "Planimetry of the alpha effective orientation area: Complex of Multi-slice CT and MRI" (European Journal of Radiology 2011, 77, p. 426) suggest the use of an image of an open Valve to measure the Valve opening using several selected slices and delineated apparent Valve pores. The measured area of such an aperture is then used to assess the extent of stenosis. This technique is called AV area measurement.

However, for AV area measurements from CT or MRI, only two-dimensional (2D) incisions are analyzed. It was not analyzed whether the valve leaflets meet at commissure lines in some other region downstream. Therefore, such 2D measurements cannot assess the effect on three-dimensional (3D) blood flow. Therefore, the relationship between such a measurement area and the physiological effects of the stenotic valve (e.g. an increase in the pressure gradient) is not clear.

Disclosure of Invention

It is an object of the invention to derive target values for physiological parameters of a patient under consideration from patient-specific boundary conditions.

This object is achieved by an apparatus according to claim 1, a method according to claim 5 and a computer program product according to claim 15.

Thus, a volume mesh of cardiovascular structures (including left ventricular outflow tract, aortic root including Aortic Valve (AV), and ascending aorta) is generated based on segmented digital images of the cardiovascular structures, and cardiac ejection output (cardiac ejection output) per heart beat is estimated from the volume or temporal behavior of the volume of the left ventricle in different filling states of the patient at two or more different points in time. At least one patient-specific boundary condition (which may include a time-dependent boundary condition) of the cardiovascular structure is then derived from the cardiac ejection output of each heart beat, and a simulated blood flow is obtained by simulating blood flow through the volume mesh taking into account the patient-specific boundary condition.

Thus, the blood flow through the patient-specific geometry of the target cardiovascular structure under patient-specific boundary conditions is derived from the cardiac ejection output per heart beat. The simulation results yield target values for physiologically relevant parameters, such as one or more of pressure drop, mean blood residence time, flow rate, wall shear stress, and blood swirl in the cardiovascular structure.

According to a first aspect, a modeling circuit may be provided for generating the volumetric mesh of the cardiovascular structure based on a segmented digital image of the cardiovascular structure. Thus, the volumetric mesh may be generated directly without the need to export or load from a remote device or network.

According to a second aspect which may be combined with the above first aspect, the digital image may be a CT image or an MRI image or an ultrasound image. Thus, the proposed solution can be used for a wide range of medical imaging systems.

According to a third aspect which may be combined with the first or second aspect above, the digital image may be segmented by using model-based segmentation to obtain a surface mesh of the target cardiovascular structure. Thereby, the volumetric mesh may be easily obtained by transforming or transforming the surface mesh into the volumetric mesh.

According to a fourth aspect which may be combined with any one of the above first to third aspects, the simulation may be accomplished by Computational Fluid Dynamics (CFD) or fluid-solid interaction (FSI) simulation. This facilitates automation of the process of creating the computer model.

According to a fifth aspect which can be combined with any one of the above first to fourth aspects, the cardiac ejection output per heart beat can be estimated based on the cardiac gated digital image. This measure ensures the correct time of image generation.

According to a sixth aspect which can be combined with any one of the above first to fifth aspects, the cardiac ejection output per heart beat can be estimated based on digital images of the ventricle in a maximum filling state and a minimum filling state. This provides a straightforward solution based on both images. In a specific example, the cardiac ejection output per heart beat may be estimated based on the volume of the left ventricle at the end of systole and the end of diastole of the patient.

According to a seventh aspect which may be combined with any one of the above first to sixth aspects, the estimated cardiac ejection output per heart beat may be used to define a blood flow from a heart chamber to the cardiovascular structure. According to a specific example of the fifth aspect, the at least one patient-specific boundary condition may be derived by estimating a flow distribution through the ventricular outflow tract and its temporal behaviour. Thus, the (flow) boundary condition may be determined based on the ventricular ejection fraction by image analysis (e.g. estimating the pressure drop over the target cardiovascular structure via (CFD or FSI) simulation). Thus, a complete heart simulation is no longer needed, which is very time consuming, very complex and cannot always be done with available clinical data. The flow distribution can be estimated by defining a quadratic distribution or velocity distribution of the pulsating flow.

It is to be understood that similar and/or identical preferred embodiments of the apparatus, method and computer program product according to the above-described aspects of the invention, in particular preferred embodiments defined by other aspects of the invention, are described.

It should be understood that the preferred embodiments of the present invention may also be any combination of aspects of the present invention.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

Drawings

In the drawings:

FIG. 1 shows a schematic block diagram of the generation and use of patient-specific boundary conditions for simulating blood flow, according to an embodiment of the invention;

2a-f show schematic reformatted views of a segmented valve for the case of an open, calcified mid-orifice and closed valve, respectively;

FIG. 3 shows a graph with volume curves of a heart chamber extracted by model-based segmentation; and

fig. 4 shows a schematic and exemplary visualization of a simulation of blood flow through an aortic valve.

Detailed Description

Embodiments are now described based on simulation of blood flow through the Left Ventricular (LV) outflow tract and the patient-specific geometry of the ascending aorta (as an example of a blood cavity or cardiovascular structure near the heart) under patient-specific boundary conditions derived from the cardiac ejection output per heart beat, which blood volume can be calculated from (at least) two images of the LV in maximum and minimum filling states (e.g., end diastole, end systole). The geometry of the LV outflow tract, the aortic root including the AV, and the ascending aorta and ventricle volumes can be obtained automatically by model-based segmentation.

Fig. 1 shows a schematic block diagram of the generation and use of patient-specific boundary conditions for simulating flow through an aortic valve. The blocks of fig. 1 may be regarded as hardware circuits adapted to perform the respective functions or as steps of a corresponding method or as a process which is implemented as a software program comprising code means for producing the relevant functions when run on a computer or processor system.

First, in a segmentation step or circuit (CT (OV))10, the LV outflow tract, the aortic root including AV, and the ascending aorta are separated into an Open Valve (OV) state in the CT image to obtain a surface mesh of the entire blood cavity. This can be done using model-based Segmentation, as described in "Segmentation of the heart and grease fields in CT images using a model-based adaptation frame" (Medical Image Analysis 2011, 15(6), pages 863-. In general, segmentation is the process of partitioning a digital image into a plurality of segments (i.e., sets of pixels). In segmentation, voxels are assigned to specific structures, for example by adding labels or colors or contours, etc. This can be achieved by typical image segmentation methods such as thresholding, edge detection, region growing, etc. Then, in a modeling step or circuit (VM)12, from the surface mesh obtained from the segmentation step or circuit 10, a volumetric mesh for Computational Fluid Dynamics (CFD) or fluid-solid interaction (FSI) or other types of simulations is generated using known gridding tools. Suitable meshing tools (e.g., TetGen or NetGen) may include techniques that generate different tetrahedral meshes from a three-dimensional set of points or domains with piecewise linear boundaries.

According to the present embodiment, the model-based segmentation (MBS) as described above is used in the first (LVV (ed)) extraction step or circuit 22 and the second (LVV (sys)) extraction step or circuit 23 to extract the change over time of the Left Ventricular Volume (LVV) from the Electrocardiogram (ECG) gated CT images obtained in the first imaging step or circuit 20 and the second imaging step or circuit 30 (refer to fig. 3 below). More specifically, the Left Ventricle (LV) in the maximum and minimum filling states (end of diastole, end of systole) can be obtained from the first and second imaging steps 20, 30, respectively, and can be used to estimate the flow or volume or temporal appearance of the blood pumped per heartbeat (i.e. cardiac ejection output). This flow or volume or temporal appearance of the blood is then used in an estimation step or circuit (fl (av))40 to define the blood flow from the left ventricular outflow tract through the aortic orifice into the aorta.

Fig. 2a to 2f show schematic reformatted cross-sectional top and side views of sample results for a segmented valve for an opening (fig. 2a (top view), fig. 2d (side view)), a middle opening for calcification (fig. 2b (top view), fig. 2e (side view)), and for a closed valve (fig. 2c (top view), fig. 2f (side view)), respectively. The double arrow 100 marked in fig. 2d and 2f indicates the width of the valve hole.

Fig. 3 shows a graph with volume curves of four heart chambers (left atrium (LA), Left Ventricle (LV), Right Atrium (RA), Right Ventricle (RV)) extracted from an ECG gated CT data set by a model based segmentation of the extraction steps or circuits 22, 23.

To define the patient-specific boundary conditions (i.e., the flow at the LV outflow tract), the flow distribution over the outflow tract and its temporal appearance can be estimated in an estimation step or circuit 40. For temporal behavior, it may be assumed, for example, that there is no flow through the aortic valve during a predetermined portion (e.g., between 40% and 10%) of the cardiac cycle. Between (e.g., -10% -40%), a constant flow or volume flow curve derived from the LV volume curve in fig. 3 may be used. The flow on the LV outflow tract may be defined, for example, by a quadratic profile (a profile of constant flow in the tract) or a velocity profile using a Womersley number of pulsatile flows.

In a subsequent CFD simulation step or circuit 50, the flow through the open valve is simulated by CFD to estimate the pressure drop for the open valve. This may be achieved by specifying blood flow behavior and properties at the boundaries of the volume grid of the blood cavity resulting from the modeling step or circuit 12, while taking into account the above-mentioned patient-specific boundary conditions obtained from the estimation step or circuit 40. Furthermore, in order to obtain a complete simulation of the blood flow through the aortic valve, fluid-solid interactions may be considered, thus also interactions with the elastic vessel wall. The results of the CFD simulation may be analyzed to estimate, for example, the pressure drop across the aortic valve or other physiological parameters such as mean blood residence time across the aortic valve, flow rate, wall shear stress, and blood swirl.

Finally, the results of the flow simulation may also be visualized and/or quantified in an optional visualization and/or quantification step or circuit (V/Q)60, and virtual doppler ultrasound images may be generated to allow the physician to evaluate the results. Such visualization may be based on an analysis method that analyzes the simulated blood flow and shows attributes (e.g., streamlines, striae, and traces). The blood flow may be given in a finite representation or as a smoothing function. Alternatively, a texture convection approach may be used that "warps" the texture (or image) according to the flow. Numerical or qualitative values of one or more of the above physiological parameters may be added to the visualization to allow comparison with standard values

Fig. 4 shows a visualization of an exemplary simulation of blood flow through an aortic valve.

The proposed solution may be used to quantify AS or other cardiovascular diseases or even other blood flow related features of cardiovascular structures by simulation in a clinical workstation or other computer system based on image data obtained from CT or MRI or ultrasound or other imaging modalities.

In summary, methods and apparatus have been described for simulating blood flow through a patient-specific geometry of a cardiovascular structure (such as the left ventricular outflow tract, the aortic root including AV, and the blood cavity of the ascending aorta, ventricular volume, aorta, or any other cavity through which blood flows) under patient-specific boundary conditions derived from cardiac ejection output per heart beat. The cardiac ejection output may be estimated from the volume of the patient's heart chamber in different filling states at two or more different points in time. In the case of AV-related simulations, AV geometry and ventricular volume can be automatically obtained by model-based segmentation. In a first step, the blood cavity is segmented in a CT image. A volumetric mesh for CFD simulation may be generated from the surface mesh. Model-based segmentation may be used to extract volume changes over time. The flow distribution on the outflow tract and its temporal behaviour are then defined. The results of the CFD simulation may be analyzed to estimate physiological parameters (e.g., pressure drop, etc.) across the aortic valve. The results of the flow simulation may also be visualized and a "virtual doppler ultrasound" image may be generated to allow the physician to evaluate the results.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive. The invention is not limited to the disclosed embodiments.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the words "a" or "an" do not exclude a plurality. A single processor or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The foregoing description details certain embodiments of the invention. It should be appreciated, however, that no matter how detailed the foregoing appears in text, the invention can be practiced in many ways and is therefore not limited to the disclosed embodiments. It should be noted that the use of particular terminology when describing certain features or aspects of the invention should not be taken to imply that the terminology is being re-defined herein to be restricted to including any specific characteristics of the features or aspects of the invention with which that terminology is associated.