Improved Simulation of Endoprosthesis Deployment in Real Time - Patent application

Abstract

To provide improved simulation of the deployment of an endoprosthesis in real time.SOLUTION: A device for medical imaging by X-ray is provided. More specifically, it relates to the simulation of the deployment of an endoprosthesis in order to assist a surgeon in an intravascular surgical procedure. The present invention makes use of a single 2D image in order to determine specific characteristics of a simplified model of the endoprosthesis, namely 2D positions and deployment value of the stents, to determine the inherent rotation of at least one stent, and then to determine the deployment of a model representing the structure of the stents, initialized on the basis of the preceding steps, in a 3D model of a vascular structure.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to the field of medical x-ray systems, and more particularly to radiological systems used in endovascular surgery of abdominal aortic aneurysms. [Background technology]

[0002] Abdominal aortic aneurysms can be treated by traditional open surgery or endovascular surgery. During endovascular treatment, the surgeon does not have direct access to the surgical site. In contrast, in endovascular surgery, the femoral artery is cut open at the groin and a very flexible metal lead is inserted. By pushing on this lead, the device, including the endoprosthesis, can be moved to the area of ​​the abdominal aortic aneurysm. Once the surgeon deems the endoprosthesis to be in the correct location, he or she decides to release the endoprosthesis, which causes it to automatically deploy.

[0003] Accurate positioning of the endoprosthesis is therefore essential. Indeed, the endoprosthesis must be positioned precisely and must not occlude the arteries branching off from the main artery. In the most complicated cases, so-called fenestrated endoprostheses contain openings that must be positioned precisely opposite the ostium of the second artery. For example, these openings must be positioned opposite the junction of the aorta and the renal arteries branching off from the aorta. It is therefore essential to position the endoprosthesis precisely in order to avoid blocking these junctions and thus blocking the renal arteries.

[0004] To guide the above mentioned maneuvers, the surgeon uses a mobile imaging system to precisely place the endoprosthesis that redirects the blood flow. These systems, also called mobile C-arms (or block amplifiers), acquire X-ray images while the surgeon performs the intervention, allowing the position of the instruments (catheters, prostheses, etc.) to be monitored in real time and as non-invasively as possible. The majority of these systems make it possible to acquire two-dimensional images from a video image stream of up to 30 images per second. The practitioner then uses these images to mentally reconstruct the geometry of the instruments and the arteries to verify the positioning in real time. X-ray imaging requires the injection of a contrast agent. The contrast agent is essential to make the aorta X-rayable, but has the disadvantage of being toxic. This limits the number of possible injections and imaging times.

[0005] The step of positioning the endoprosthesis can in some cases be very complicated, requiring an increased number of images, and therefore an increased amount of patient exposure and contrast injected. The probability of postoperative complications is also increased. In the short term, this is due to blood loss and insufficient cleaning of the area blocked by the surgical instruments. In the medium and long term, an incorrect positioning of the endoprosthesis leads to the risk of leakage and thrombosis. The deployment of the endoprosthesis in the aorta occurs in three dimensions. It therefore turns out that a single two-dimensional image is not sufficient to allow the surgeon to clearly evaluate the deployment of the prosthesis. The possibility of three-dimensional visualization of the surgical site would therefore be of great advantage to the surgeon, allowing a faster and more accurate positioning of the instruments while reducing the number of angiograms. Summary of the Invention [Problem to be solved by the invention]

[0006] Currently, there are several methods that allow the abovementioned 3D visualization. However, these methods are still based on acquiring multiple 2D images from different viewing angles for the purpose of 3D reconstruction. They therefore lead to multiple injections of contrast agent and longer operation times due to the need to acquire multiple images at different angles.

[0007] Therefore, there is a need for an instrument to aid in surgical procedures that allows a surgeon to visualize instruments and their configurations within a patient's aorta in near real-time and in three dimensions. [Means for solving the problem]

[0008] To this end, the invention relates to a method comprising: taking a two-dimensional image of a vascular structure by X-rays, obtaining a three-dimensional model of the vascular structure, obtaining a model of an endoprosthesis comprising a number of stents in the vascular structure, determining for each stent from the two-dimensional image at least one position, at least one orientation and at least one deployment value, simulating for each stent the deployment in the three-dimensional model of the vascular structure of a model of the stent representative of the structure of the stent, said model of the stent being initialized based on the model of the endoprosthesis, and displaying the deployed stent model.

[0009] Advantageously, the two-dimensional image defines a three-dimensional reference frame including vertical and horizontal axes and a depth axis of the image, and in the endoprosthesis model, each stent is defined by at least one position and orientation of at least one feature point defined by at least six degrees of freedom including a three-dimensional position of a first feature point of the stent in the reference frame, an angle of rotation, and at least one deployment value defined about a central axis of the stent, the model of the stent being formed by a plurality of interconnected beam elements, the method comprising: determining, from the two-dimensional image, for each stent, at least one position, at least one orientation, and at least one deployment value of at least one feature point along the vertical and horizontal axes, as well as at least one deployment value of the stent, and determining the angle of rotation for at least one stent.

[0010] Advantageously, the position and orientation of each stent is defined by the three-dimensional location of three feature points, each corresponding to the center, the upper and lower ends of the stent along the central axis, and the rotation of the stent about the central axis.

[0011] As an advantageous feature, determining the angle of rotation for the at least one stent includes determining the angle of rotation at which at least one three-dimensional positional projection of the at least one radiopaque marker onto the stent best matches at least one image of the at least one marker on the two-dimensional image.

[0012] As an advantageous feature, the angle of rotation is obtained as a function of the angle of rotation by executing a loop which minimizes the distance between at least one projection on the two-dimensional image and at least one image of at least one marker.

[0013] As an advantageous feature, determining the angle of rotation for at least one stent comprises modelling the stent in the form of beam elements of a finite element model between a feature point representing an upper end of a central axis of the stent and a feature point representing a lower end of the central axis of the stent, the feature point being movable along a depth axis.

[0014] Advantageously, the endoprosthesis is represented in the form of a finite element model, each stent being modeled by beam elements, successive stents being connected to each other by at least one beam element, the positions of feature points of the stents whose maximum deployed diameter is equal to or greater than the diameter of the vascular structure in the deployed position being fixed along the vertical, horizontal and depth axes, the positions of feature points of the stents whose maximum deployed diameter is smaller than the diameter of the vascular structure in the deployed position being fixed along the vertical and horizontal axes and movable along the depth axis, and the positions of feature points of the stents whose maximum deployed diameter is smaller than the diameter of the vascular structure in the deployed position along the depth axis being determined by mechanical balance of the finite element model.

[0015] As an advantageous feature, the display of the deployed stent model includes a superimposed projection of the stent model onto a two-dimensional image of the vasculature.

[0016] As an advantageous feature, the representation of the deployed stent model includes a three-dimensional representation of the deployed stent model and a three-dimensional model of the vascular structure.

[0017] Advantageously, the three-dimensional model of the vasculature is a finite element model, which represents the centreline of the vasculature by means of beam elements.

[0018] The invention also describes a computer program product comprising computer code elements arranged to carry out a method according to an embodiment of the invention.

[0019] The present invention also describes an apparatus comprising at least one input port configured to receive a two-dimensional image of a vascular structure imaged by X-rays and at least one computing device configured to perform a method according to an embodiment of the present invention.

[0020] Overall, the method allows for reliable and fast calculation of the deployment of an endoprosthesis in an aorta, for example, the method can be performed in about 30 seconds with standard computing tools, thus allowing for near real-time modeling of the deployment of the endoprosthesis.

[0021] The method of the present invention provides the surgeon with real-time visualization of the deployment of the endoprosthesis based on its actual position, thus allowing the surgeon to greatly improve the precision of the treatment he or she performs.

[0022] The method of the present invention eliminates the need for multiple injections of contrast agent since only a single imaging session is required to simulate the deployment of an endoprosthesis.

[0023] The method is applicable to deployed prostheses as well as undeployed or partially deployed prostheses.

[0024] Other characteristics, details and advantages of the invention will become apparent from a study of the following description with reference to the accompanying drawings, given by way of example, in which: [Brief description of the drawings]

[0025] [Figure 1]1 illustrates a medical imaging system in which the present invention may be implemented; [Figure 2a] 1 shows a perioperative two-dimensional image with contrast injection showing the endoprosthesis in the aorta. [Figure 2b] 1 shows perioperative 2-dimensional images showing the aortic endoprosthesis without contrast injection. [Figure 2c] 13A-13C show an endoprosthesis deployed within a mock-up aorta, according to a set of implementations of the present invention. [Diagram 3] 1 illustrates a method for simulating the deployment of an endoprosthesis according to a set of implementations of the present invention. [Figure 4] 1 illustrates modeling of a stent within an endoprosthesis model according to a set of example implementations of the present invention. [Diagram 5] A model of an endoprosthesis shows the deployment of a targeted stent. [Figure 6] 1 shows a two-dimensional image-based determination of the vertical and horizontal positions of feature points of a stent, and also of its deployment. [Figure 7a] 1 shows a first example of modeling stent deployment according to a set of implementations of the present invention. [Figure 7b] 13 shows a second example of modeling stent deployment according to a set of implementations of the present invention. [Figure 8] 13 shows the overlay of a simulation of stent deployment on perioperative images according to a set of implementations of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] FIG. 1 illustrates a medical image processing system in which the present invention may be implemented.

[0027] The system 100 is a mobile imaging-guided therapy system.

[0028] The system 100 includes an element called a C-arm 110 that allows for acquisition of X-ray images of a patient's body. The C-arm can rotate about different axes to image a stationary patient at different angles. The C-arm includes a control interface that allows the medical team to control the orientation and imaging.

[0029] The C-arm 110 is connected to a computing device, e.g. a computer 120, capable of generating a display of the X-ray images acquired by the C-arm 110 on a display means, e.g. a screen 121. For this purpose, the computing device 120 comprises an input port for receiving the peri-operative images. The computing device 120 also comprises at least one computing part (e.g. a processor) for processing the images acquired by the C-arm. For example, the processor can perform a pre-analysis of the images and overlay on the images items of information of interest to the medical team (e.g. the time of taking the image, the patient's temperature, blood pressure, etc.).

[0030] Splitting the system into two devices, the C-arm 110 which acquires images and the computing device 120 which processes and displays the images, allows for great flexibility in use of the C-arm 110, which can be kept mobile even if the position of the display screen 121 remains fixed.

[0031] In one set of embodiments of the present invention, the device 120 also allows visualization of the deployment of the endoprosthesis in two or three dimensions, as described below.

[0032] System 100 is provided as just one example of a system in which the present invention can be implemented. The present invention can be implemented in many other medical systems. For example, image processing and display according to different imaging modes can be performed on a single device. Images can also be captured at one location and sent to another site, e.g., a remote server, for processing and display.

[0033] 2a, 2b, and 2c show perioperative 2D images of an endoprosthesis in the aorta with and without contrast injection, and an endoprosthesis deployed in a mock-up aorta according to a set of implementations of the present invention, respectively.

[0034] 2a shows a perioperative image of the aorta obtained by a device such as device 100 using X-rays and contrast agents, which makes it possible to visualize the borders of the aorta, in particular the diameter of the aorta at each point and to visualize the points where the adjacent veins branch off.

[0035] FIG. 2b shows a perioperative image 200b of the aorta acquired using X-rays with a device such as device 100, without contrast and before deployment of the stents. Without contrast, the borders of the aorta are not discernible, but the endoprosthesis stents 211b, 212b, 213b, 214b, 215b, 216b, 217b and 218b, 219b, 220b are evident. Stents 211b-218b are not deployed, stent 219b is partially deployed, and stent 220b is fully deployed. Radiopaque markers such as markers 230b, 231b are also evident. Perioperative imaging also allows the location of certain essential features that can be visualized by markers such as markers 230b, 231b. These markers can be placed at particularly important points on the endoprosthesis so that the surgeon can identify their location on the perioperative image.

[0036] During introduction of the endoprosthesis, the surgeon can take a first image with contrast to visualize the borders of the aorta, and then take one or more images without contrast to visualize the location of the stent and radiopaque markers. These two images can be superimposed to visualize the location of the stent within the aorta.

[0037] At this stage, the endoprosthesis may be undeployed, partially deployed, or fully deployed, but an image such as that of Figure 2b allows the position of the stent to be determined as described below.

[0038] This type of perioperative 2D imaging therefore provides the surgeon with a general understanding of the position and deployment of the endoprosthesis within the artery, but it has been found that this type of 2D imaging is often inadequate for evaluating the deployment that occurs in 3D.

[0039] Fig. 2c shows an image of the deployed endoprosthesis in a mockup. The image is similar to what a surgeon sees by superimposing perioperative images with and without contrast, i.e. visualizing both the endoprosthesis and the space in which it is deployed. In the example of Fig. 2c, the endoprosthesis is fully deployed. The image shows the deployed endoprosthesis in a mockup of an aorta 220. The endoprosthesis is formed by a number of stents 211, 212, 213, 214, 215, 216, 217, 218. The perioperative image thus allows a two-dimensional visualization of the position and deployment of the stents in the artery.

[0040] As will be described later, the invention allows a three-dimensional simulation and visualization of the deployment of an endoprosthesis on the basis of a two-dimensional image. In the following description, the three-dimensional deployment is performed in a reference frame R based on three axes x, y and z, which correspond respectively to the vertical, horizontal and depth axes. im The plane formed by the vertical axis x and the horizontal axis y is called the projection plane or two-dimensional image plane. However, this reference frame is provided merely as an example, and one of ordinary skill in the art will be able to select any three-dimensional reference frame that suits their needs after reviewing this disclosure.

[0041] FIG. 3 illustrates a method for simulating the deployment of an endoprosthesis according to a set of implementations of the present invention.

[0042] The purpose of method 300 is to simulate the deployment of an endoprosthesis and allow a surgeon to conveniently visualize the deployment of the endoprosthesis within an artery in three dimensions.

[0043] The method 300 includes a step 310 of acquiring a two-dimensional image 311 of the vasculature by X-ray. The two-dimensional image is a perioperative image and can be acquired by a C-arm type device such as the device 100. The images in Figs. 2a and 2b are two examples of such images. As explained above, acquiring such an image by X-ray may include the injection of a contrast agent into the vasculature. It is noted that in the following description, the method is illustrated by an example relating to the simulation of an endoprosthesis in the aorta. However, these examples are given as non-limiting examples, and the method can be applied to the simulation of an endoprosthesis deployment in any vasculature. There is no fundamental difference between the deployment of an endoprosthesis in the aorta and in other vasculature, and therefore the method can be directly applied to other vasculature. The method can also be applied to the simulation of an endoprosthesis deployment in a surgical mockup.

[0044] The capture of the two-dimensional image defines a three-dimensional reference frame for use in other parts of the method. The three-dimensional reference frame includes vertical, horizontal and depth axes of imaging. In the example of Figure 2, these axes are labelled x, y and z, respectively. However, this notation is provided merely for illustrative purposes and one skilled in the art would be able to easily name and orient the axes according to his or her needs.

[0045] The method 300 also includes obtaining a three-dimensional model 321 of the aorta, which allows the contour and volume of the aorta to be defined in three dimensions. The aorta can for example be defined by a set of three-dimensional polygons. The boundaries of the aorta can then be represented in a reference frame defined by two-dimensional imaging.

[0046] According to different embodiments of the invention, the 3D model can be acquired in different ways: for example, it can be generated by 3D imaging of the patient in advance, it can be acquired in advance and then registered in real time during surgery, or it can be created from perioperative 2D images.

[0047] In this set of embodiments, the three-dimensional model of the aorta 321 is a finite element model and includes a representation of the centerline and surface of the aorta.

[0048] In a set of implementations of the present invention, a 3D model of the aorta is obtained from perioperative 2D images, for example images acquired from a C-arm, by a method of non-rigid registration of a prior model of the aorta.

[0049] As shown above, the method for non-rigid registration of the aorta is based on a finite element model of the arterial centerline. The perioperative information items contained in the projection plane of the perioperative 2D images act as boundary conditions in the finite element model. The out-of-plane deformations are then calculated by a mechanical model.

[0050] In a set of embodiments of the present invention, the alignment method comprises the following steps. - Extraction of arterial centerlines using the Voronoi projection method introduced for example by Antiga, L. (2002). Patient-specific modelling of aortic geometry and blood flow (Politecnico di Milano). -Implementing a centerline in a finite element model based on beam elements. This can be done in different ways. Duriez, C. (2013): Real-time haptic simulation of medical procedures involving deformations and device-tissue interactions (Doctoral disseration, Universite des Sciences et Technologie de Lille-Lille I) gives an example of the implementation of the aortic centerline via a finite element model. - A first 2D / 3D non-rigid registration is performed between the perioperative images and the projection of the centerline extracted in the previous step. The non-rigid registration consists of a rigid registration and an interpolation. - Two-dimensional information items concerning the position of the aorta or the instruments during the operation are then implemented in the finite element model. The projection matrix of the perioperative images is assumed to be known. This makes it possible to calculate the backprojection line of each feature point identified on the 2D images. These information items are then implemented in the mechanical model in the form of boundary conditions, which force the points of the 3D model to move along the backprojection lines. The mechanical model thus calculates the deformations that are not included in the projection plane of the perioperative 2D images in order to reach an equilibrium state. The aortic volume is then reshaped around the updated centerline.

[0051] In a set of embodiments of the present invention, a three-dimensional model of the aorta is overlaid onto the perioperative images.

[0052] Method 300 also includes obtaining a model 331 of the endoprosthesis, in which each stent is defined with at least six degrees of freedom and at least one position and one orientation of the stent defined by deployment of the stent.

[0053] The degrees of freedom representing the position and orientation of the stent include at least one three-dimensional position of at least one characteristic point of the stent and the rotation r of the stent around the central axis. x’ According to different embodiments, the six-dimensional position of the stent can be defined in different ways, for example by the three-dimensional position of at least two feature points of the stent and the angle of rotation, or by the three-dimensional position of a single feature point of the stent and three angles of rotation. Those skilled in the art will easily be able to find a way of modeling the stent that suits their needs.

[0054] FIG. 4 illustrates modeling of a stent within an endoprosthesis model according to a set of implementations of the present invention.

[0055] FIG. 4 shows modeling 400 of a stent within an endoprosthesis model 331 .

[0056] In this example, the stent is fitted with a reference frame R im Its own reference frame R contains three axes (x', y', z') that are initially aligned with the axes (x, y, z) of stent is associated with the rotation of the stent. x’ is defined around a central axis (which can also be called the vertical axis) x'. This simplified model includes the 3D locations of three feature points P0, P1, and P2, which correspond to the center, upper end, and lower end of the stent along the central axis x', respectively. In this example, the position and orientation of the stent is therefore defined with 10 degrees of freedom (9 for the three 3D positions and 1 for the rotation).

[0057] The use of three feature points in this manner allows for a further refinement of the method for determining the location and orientation of the stent.

[0058] However, the above modeling of the stent's position and orientation is provided merely as a non-limiting example, and the stent's position and orientation can be represented in other ways, for example by the position of feature point P0 and its rotation in three directions, or by the position of feature points P1 and P2 and its rotation about axis x'.

[0059] FIG. 5 shows the deployment of a stent covered by a model of an endoprosthesis.

[0060] In a set of embodiments of the present invention, stent deployment is defined by a single value, which may be, for example, the diameter of the stent, a rate or a ratio of deployment.

[0061] Diagram 500 shows a simplified deployment of several stents. Axis 510 shows the deployment of the stents in mm. Axis 520 shows the position and length of each stent.

[0062] According to different embodiments of the present invention, it is also possible to describe the deployment of a stent according to a limited number of values ​​that represent the deployment at different characteristic points about the central axis of the stent, for example, the deployment of a stent can be described by a deployment value at the top end of the stent and a deployment value at the bottom end.

[0063] Representing the deployment of a stent by at least one value representing the level of deployment about the central axis of the stent, in combination with position and orientation values, therefore allows for a very comprehensive description of the deployment of each stent within an endoprosthesis using a limited number of parameters, the majority of which can be extracted from two-dimensional perioperative images.

[0064] Endoprosthesis model 331 thus allows for a simple modeling of the endoprosthesis and allows for the representation of the global alignment of the endoprosthesis with a limited number of degrees of freedom.

[0065] Returning to FIG. 3, method 300 includes determining 330, from the two-dimensional image, for each stent, at least one position of at least one feature point along the vertical axis (x) and horizontal axis (y), and at least one expansion value of the stent.

[0066] This step includes identifying all values ​​of the endoprosthesis model that can be obtained directly from the two-dimensional image.

[0067] FIG. 6 shows the determination of the vertical and horizontal positions of the feature points of a stent and the deployment of said stent from a two-dimensional image.

[0068] More precisely, Fig. 6 shows the image of Fig. 2c, highlighting different parameters that three-dimensionally model the deployment of the endoprosthesis. Fig. 6 thus illustrates the detection of certain values ​​of perioperative images of the aorta in two-dimensional images similar to those that a surgeon can visualize in real time. Although Fig. 2c and Fig. 6 show a deployed endoprosthesis in an aortic mockup, the elements shown in Fig. 6 are also applicable to images showing a contrast-enhanced aorta superimposed with an image of the endoprosthesis, and images of undeployed or partially deployed endoprosthesis.

[0069] Three vignettes 610, 620 and 630 respectively show three examples of determining the location of stent feature points, stent deployment and association to the aortic centerline in image 200.

[0070] In particular, the two-dimensional image allows the reference frame R im The position of each feature point of the stent along the x and y axes of the image 200b can be obtained directly. The reading can be done manually from the information items shown on the screen or semi-automatically from a process in which the position of the center of gravity of the stent is detected. In the example shown in FIG. 6, the stent 211 has three feature points 211-P1, 211-P0 and 211-P2 associated with it according to the model shown in FIG. 4. The analysis of the image 200b therefore makes it possible to directly estimate for each stent the position of the feature points 211-P0, 211-P1 and 211-P2 along the x and y axes. For example, these points may correspond to the points 211b-0, 211b-1 and 211b-2 of the image 200b, whose position can be determined directly by the analysis of the image 200b. According to different embodiments of the invention, the positions x, y of the feature points are calculated based on the position of the feature points in the reference frame R. im The feature points can be determined relative to a single origin of the aorta or relative to the center point of the aorta. The stent is then positioned in the simulation according to the locations of the feature points thus determined.

[0071] Vignette 620 illustrates the determination of at least one expansion value for each stent about the central axis of the stent. In the example of FIG. 6, each stent is associated with a top expansion value and a bottom expansion value. For example, stent 211 is associated with a top expansion value 211-D1 and a bottom expansion value 211-D2. Again, the expansion values ​​of the stent may be obtained directly by analysis of image 200. In the example of vignette 620, the stent has been deployed and the expansion values ​​may be obtained directly by measuring the deployment of the stent on the image, either manually or automatically by image analysis.

[0072] In embodiments where the endoprosthesis is not deployed or is not fully deployed, the deployment value can be determined as the diameter of the aorta at the time of deployment, if the maximum deployment diameter of the endoprosthesis is equal to or greater than said diameter of the aorta at the time of deployment. In the opposite case, the deployment value corresponds to the maximum deployment of the endoprosthesis. In fact, the final deployment diameter of the endoprosthesis at that time is in this case constrained by the diameter of the aorta or the diameter of the stent.

[0073] The vignette 630 shows the association of the stent feature points with the aortic centerline.

[0074] The centerline of the aorta can be obtained by projection of a previously obtained 3D centerline or by methods of skeletonization of 2D images (many methods of skeletonization of 2D images are known, e.g. Couprie, M., Coeurjolly, D., & Zrour, R. (2007): Discrete bisector function and Euclidean skeleton in 2D and 3D (Image and Vision Computing, 25(10), 1543-1556)). In a set of embodiments of the present invention, the positions of the stent feature points along the z-axis are initialized on the centerline of the aorta.

[0075] As shown in FIG. 6, step 330 of determining the horizontal and vertical position and deployment of the stent can be performed by direct analysis of the perioperative two-dimensional images, either manually or automatically by image analysis.

[0076] This determination can therefore be performed extremely quickly. Step 330 can therefore be performed in real time once the two-dimensional image has been captured. Furthermore, this step can be performed with high precision, within a millimeter, for the determined values.

[0077] Certain features of the endoprosthesis model cannot be directly measured by direct analysis of the images. For example, the location of feature points on the depth axis z and the rotation of the stent cannot be directly determined. These values ​​can be initialized to default values. For example, the location of the points on the depth axis can be initialized to be located at the centerline of the aorta, and the rotation of the stent about axis x' can be initialized to zero.

[0078] In a set of embodiments of the present invention, the mechanics of the endoprosthesis are modeled in the form of a finite element model, in which each stent is modeled by a beam element, and the stents are connected to each other by small beam elements.

[0079] In a set of embodiments of the invention, a number of (e.g., five) connecting beam elements are arranged in succession between the ends of the beam element representing the stent. Stiffness matrices can be associated with these connecting beam elements, and their mechanical characteristics are different from those of the stiffness matrix of the beam element representing the stent. Thus, the rigid body behavior of these connecting beam elements is relatively small. This allows the mechanical balance between successive stents to be precisely modeled.

[0080] Stents whose maximum deployed diameter at the deployment site is equal to or greater than the diameter of the aorta are considered to be constrained, i.e., the positions of the feature points along axes x, y, and z are fixed. In fact, the positions of the feature points will be completely constrained by the volume of the aorta at the time of deployment. In contrast, those whose maximum deployed diameter is smaller than the diameter of the aorta are considered to be "free", i.e., the feature points are constrained from movement along the horizontal axis x and the vertical axis y, but are free to move along the z axis. The positions of the feature points along the depth axis z are then defined by the mechanical balance of the finite element model.

[0081] This allows obtaining a precise 3D position of the stent, whose position is not completely constrained by the volume of the aorta, while still taking into account the balance of mechanical forces within the aorta.

[0082] Locating the stent feature points on the aortic centerline allows the method to achieve a good balance between computation time and accuracy.

[0083] Returning to FIG. 3, method 300 includes a step 340 of determining an angle of rotation of at least one stent of the endoprosthesis.

[0084] According to different embodiments of the invention, the step performed separately for each stent can be performed for all or some of the stents of the endoprosthesis, for example for each stent of the endoprosthesis, or only for certain essential stents, for example the stent containing the window placed opposite the ostium. The surgeon can also manually select the stents for which the step is performed according to his needs.

[0085] In a set of embodiments of the present invention, the rotation r for at least one stent x’ The angle is determined by the rotation angle r at which the projection of the position of at least one radiopaque marker best matches the image of that marker on the two-dimensional image. x’For example, in image 200, also shown in vignettes 610, 620, and 630 of FIG. 6, stent 211 includes a certain number of radiopaque markers, such as markers 230, 231. The locations of these radiopaque markers are known within a simplified model of the stent. Thus, knowing the stent deployment value, the rotation r x’ For each value of the angle, the three-dimensional position of the radiopaque marker can be projected onto the two-dimensional image to see if it matches the position of the radiopaque marker on the two-dimensional image. This comparison can be performed for one or more markers.

[0086] r x’ The determination of can therefore be carried out in different ways. For example, the rotation r x’ The angle of rotation r is calculated by running a loop that minimizes the distance between the projection of the 3D position and the image of at least one marker on the 2D image. x’ can be obtained as a function of the angle.

[0087] Therefore, the angle r x’ can be iteratively modified, and at each iteration, the position difference between the projection of the 3D position in the model onto the 2D image and the image acquired by X-ray can be calculated for each marker. When multiple markers are used, the absolute values ​​of the position differences can be summed or calculated separately. Thus, the angle r x’ The value of is determined, for example, by a gradient descent algorithm in a stochastic method or by the rotation r x’ Any other algorithm capable of identifying a global minimum of the difference between the projections of the 3D positions of the markers and their images as a function of can be determined iteratively to minimize the positional difference between the projections of the 3D positions and the images of one or more markers on the 2D image. According to different embodiments of the invention, such an algorithm can be initialized with a single starting point or with multiple starting points to avoid convergence towards local minima. Any minimization algorithm can be used here.

[0088] The above is the rotation of the stent.x’ This provides a simple and quick method for determining

[0089] The method 300 then includes, for each stent, simulating the deployment of a three-dimensional model of the aorta 311 of a model of a stent 351 formed by a plurality of beam elements and initialized based on the model 331 of the endoprosthesis 210 .

[0090] Once the parameter values ​​of the endoprosthesis model 331, in which each stent is represented in a simplified manner, have been determined, the step includes using these parameter values ​​to initialize a more complex model of each stent to simulate its deployment in a three-dimensional model of the aorta.

[0091] In cases where the endoprosthesis has already been deployed, this step allows the actual deployment of the endoprosthesis to be modeled in three dimensions, and in cases where the endoprosthesis has not been deployed or is not fully deployed, this step allows the surgeon to visualize what the deployment of the endoprosthesis would look like if they decided to deploy it in its current position.

[0092] 7a and 7b show two examples of modeling stent deployment according to a set of implementations of the present invention.

[0093] The stent model 351 is formed from a number of beam elements that model the stent. The number of beam elements can vary depending on the desired complexity. For example, the stent model 351 can be formed from about 100 beam elements.

[0094] Figure 7a shows the initialization of a model 700a (corresponding to the example of model 351) within a three-dimensional model of the aorta 330. As explained above, steps 330, 340 make it possible to determine, for each stent, the characteristics of the simplified model, i.e. the position of the feature points, the rotation around the central axis, etc. These values ​​make it possible to initialize the positions and orientations of the beam elements of the models 351, 700a that represent the structure of the stent.

[0095] In the example of Fig. 7a, the stent has not yet been deployed. To simulate the deployment of the stent, it is sufficient to simulate the expansion of the beam elements from their initialization positions to the limits of the 3D model 330 of the aorta.

[0096] Figure 7b shows a stent model deployed within a three-dimensional model of the aorta 330. As explained above, model 700b is formed by a number of beam elements, e.g., elements 710b, 711b, 712b, 713b. The stent can then be deployed to its maximum expansion or until the beam elements reach the limits of the aorta, e.g., at points 720b, 721b.

[0097] The finite element model makes it possible to simultaneously take into account the constraints within the stent and the interaction of the stent with the aorta.

[0098] Because a finite element model representing the stent structure is initialized based on a pre-computed simplified model, simple simulations of stent deployment can be performed quickly, while at the same time providing an extremely accurate model of stent deployment.

[0099] Thus, method 300 as a whole allows for reliable and fast computation of the deployment of an endoprosthesis within an aorta. For example, the method can be performed in about 30 seconds with standard computing tools, thereby allowing for near real-time modeling of the deployment of an endoprosthesis.

[0100] This result is possible due to the fact that a complete model (models 351, 700a, 700b) containing multiple elements and modeling the structure of each stent has been initialized in the previous steps and only needs to be deployed. Although it would be possible to directly model the deployment of a complete model representing the structure of each stent of the endoprosthesis without relying on prior assumptions, this would require a significant amount of time that is not consistent with performing the operation in real time.

[0101] Returning to Figure 3, method 300 includes a step 360 of displaying a model of the stent deployment. This display may be in two dimensions by superimposing a projection of the stent deployment onto a perioperative two-dimensional image such as image 200, or in three dimensions by displaying a three-dimensional model of the stent deployment and aorta 330. The display may be shown, for example, on the screen 121 of the medical imaging device.

[0102] Given that the method allows for highly accurate and real-time simulation of endoprosthesis deployment, display 360 allows the surgeon to visualize the deployment of the endoprosthesis in real-time based on its actual location, thus greatly improving the precision of the procedure performed by the surgeon.

[0103] When the method is applied to a deployed endoprosthesis, the surgeon can visualize the deployment in three dimensions. When the method is applied to a non-deployed endoprosthesis, the surgeon can visualize what the deployment of the endoprosthesis would look like in three dimensions if they decided to deploy based on their current location.

[0104] Furthermore, the method eliminates the need for multiple injections of contrast agent since only a single imaging session is required to simulate the deployment of the endoprosthesis.

[0105] FIG. 8 shows the overlay of a simulation of stent deployment with a set of implementations of the present invention onto peri-operative images.

[0106] Image 800 shows the superimposition of a simulation of the deployment of an endoprosthesis onto a two-dimensional image acquired from the C-arm. As explained above, the present invention also allows a three-dimensional representation of the simulation of the deployment of an endoprosthesis on a three-dimensional model of the aorta. With three-dimensional visualization, the surgeon can manipulate the representation to visualize the prediction of the deployment at different viewing angles.

[0107] In either case, the surgeon can visualize a simulation of the endoprosthesis deployment in real time.

[0108] The above examples illustrate the ability of the present invention to make endoprosthesis deployment determinable, but they are provided merely as examples and in no way limit the scope of the invention as defined in the following claims. [Explanation of symbols]

[0109] 100 Systems 110 C-arm 120 Computer 121 Display screen 200b Perioperative Imaging 210 Endoprosthesis 211~218 Stents 211-P1, 211-P0, 211-P2 Features 211-D1, 211-D2 expansion value 211b~220b stent 220 Aorta 230,231 Markers 230b,231b Marker 300 Method for simulating deployment of an endoprosthesis 330 Aorta 400 Modeling 500 Stent deployment 510,520 Axis 610,620,630 Stent feature point association 700a Aortic Model 700b stent model 710b, 711b, 712b, 713b Beam elements 720b,721b Breaking point 800 Superimposing simulation of endoprosthesis deployment onto 2D images P0, P1, P2 feature points R im ,R stent Reference Frame

Claims

1. A method (300) implemented by an imaging system comprising an imaging device and a computing device (120) comprising a computing portion, the imaging device being connected to the computing device, the method comprising: - imaging (310) by an imaging device of a vascular structure by X-ray and of a two-dimensional image (311) of an endoprosthesis, including a number of stents; - obtaining, by a computational unit, a three-dimensional model (321) of said vascular structure; - obtaining, by a computational unit, a model (331) of an endoprosthesis (210) including a plurality of stents in said vascular structure; - for each stent, at least one position, rotation of the stent around its central axis (r ｘ’ Determination (330, 340) by a calculation unit of the angle of the rotation of the yaw axis and at least one expansion value; - simulation, by a calculation unit, of the deployment (350) of a model (351) of the stent, representing the structure of the stent, in the three-dimensional model (321) of the vascular structure from the values ​​determined in the determination, the model of the stent being initialized based on the model (331) of the endoprosthesis (210); - displaying (360), by a computing device, of the stent model deployed in said simulation on one or more display screens; The method further comprises: determining a rotation (r ｘ’ ) angle by a calculation unit, the at least one three-dimensional position projection of at least one radiopaque marker onto the at least one stent best corresponding to at least one image of the at least one radiopaque marker on the two-dimensional image. ｘ’ ) the determination of an angle of.

2. - the two-dimensional image (311) is fitted to a three-dimensional reference frame (R) which includes the vertical (x) and horizontal (y) axes of the image as well as the depth axis (z). ｉｍ ) is defined, - in the model of the endoprosthesis, each stent has - The following elements: the three-dimensional position of a first characteristic point (P0) of said stent in said three-dimensional reference frame, - the rotation (r ｘ’ ) angle, - said at least one deployment value defined about a central axis of said stent; at least one position and orientation of at least one feature point (P0, P1, P2) defined by at least six degrees of freedom, including - the model of the stent is formed by a plurality of interconnected beam elements, The method further comprising: - determination (330, 340) by a calculation unit of at least one position, at least one orientation and at least one expansion value of the at least one feature point along the vertical axis (x) and the horizontal axis (y) and of the at least one expansion value of the stent for each stent from the two-dimensional image; - rotation (r ｘ’ 2. The method of claim 1, further comprising: determining (340), by a calculation unit, the angle of

3. 3. The method according to claim 1 or 2, wherein the position and orientation of each stent is defined by the three-dimensional positions of three feature points (P0, P1, P2) each corresponding to the center, the upper and lower ends of the stent along a central axis (x'), and the rotation of the stent around the central axis (x').

4. The rotation (r ｘ’ ) is determined by performing a loop that minimizes the distance between the at least one three-dimensional position projection and the at least one image of the at least one radiopaque marker on the two-dimensional image. ｘ’ 4. The method according to claim 1, wherein the angle is obtained as a function of the angle of the axial direction of the beam.

5. Rotation (r ｘ’ 5. The method according to claim 1, wherein said determining (340), by a calculation unit, of the angle of (a) from the center axis of the stent to the center axis of the stent comprises modeling the stent in the form of beam elements of a finite element model between a feature point (P1) representing an upper end of the central axis of the stent and a feature point (P2) representing a lower end of the central axis of the stent, said feature points being movable along a depth axis (z).

6. - the endoprosthesis is represented in the form of a finite element model, each stent is modeled by a beam element, successive stents being connected to each other by at least one beam element; - the locations of the feature points of the stent, whose maximum deployed diameter is equal to or greater than the diameter of the vascular structure in a deployed position, are fixed along the vertical (x), horizontal (y) and depth (z) axes; - the location of the feature of the stent, whose maximum deployed diameter is smaller than the diameter of the vascular structure in the deployed position, is fixed along the vertical (x) and horizontal (y) axes and movable along the depth axis (z); The method of claim 5, wherein the locations of the feature points of the stent whose maximum deployed diameter is smaller than the diameter of the vascular structure in the deployed position along the depth axis (z) are determined by mechanical balance of the finite element model.

7. The method of any one of claims 1 to 6, wherein the representation (360) of the deployed stent model comprises a representation superimposed on a projection of the stent model (351) onto the two-dimensional image (311) of the vascular structure.

8. The method of any one of claims 1 to 6, wherein the representation (360) of the deployed stent model comprises a three-dimensional representation of the deployed stent model and the three-dimensional model (321) of the vascular structure.

9. The method according to any one of claims 1 to 8, wherein the three-dimensional model (321) of the vasculature is a finite element model representing a centreline of the vasculature by beam elements.

10. A computer program product comprising computer code elements configured to carry out the method of any one of claims 1 to 9 when executed on a computing part of a computing device.

11. An imaging system comprising an imaging device and a computing device (120) comprising a computing unit, the imaging device being connected to the computing device; an imaging device configured to take two-dimensional images (311) of the vascular structure and of the endoprosthesis, including the plurality of stents, by x-ray; The computing device at least one input port configured to receive a two-dimensional image of a vasculature imaged by x-ray; At least one computing unit, obtaining a three-dimensional model (321) of the vascular structure; obtaining a model (331) of an endoprosthesis in a vascular structure; From the secondary images, at least one location, rotation of the stent around its central axis (r ｘ’ ) and at least one expansion value; a calculation unit configured to simulate, for each stent, the deployment in a three-dimensional model of the vascular structure (321) of a model of the stent (351) representative of the structure of the stent from the values ​​determined in the determination step, said model of the stent being initialized based on a model of the endoprosthesis (331); Equipped with a computing device configured to display, on one or more display screens, the stent model deployed in the simulation step; Rotation (r ｘ’ ) by the calculation unit is determined based on the angle of rotation (r ) of at least one three-dimensional position projection of at least one radiopaque marker onto the at least one stent that best corresponds to at least one image of the at least one radiopaque marker on the two-dimensional image. ｘ’ ) angle determination.

Images