Method for determining the position of an implantable medical device at a deployed location after deployment in a vascular structure

Abstract

The present invention relates to a method for determining the positioning of an expandable medical device-type implant at a deployment position, the method comprising the following steps: from a three-dimensional image of an area of ​​interest including a vascular structure: determining a centerline of the vascular structure; positioning the IMD around the centerline based on an initial position; simulating the final position of the IMD after deployment as the stress exerted on the IMD by the wall of the vascular structure changes, wherein the centerline is determined including placement points so as to minimize the travel time of the fluid along the points between the re-input point and the output point, and the simulation of the final position of the IMD takes into account the level of longitudinal push and pull intended to be applied to the IMD during implantation of the IMD.

Description

Technical Field

[0001] The present invention relates to the field of digital simulation of vascular implants before and during operation of the implant.

[0002] More specifically, the present invention relates to the prediction of the mechanical behavior of an implantable medical device (or IMD) for which a three-dimensional mapping of a vascular structure (such as an artery) with a localized pathology (such as an aneurysm) is available prior to inserting the implant along an intravascular route. This prediction is useful for the clinician to select the optimal size and optimal initial positioning of the device during an intervention, or even to select the optimal model. Background Art

[0003] It is common practice to treat arteries affected by, for example, aneurysms using deployable, implantable medical device (IMD) type implants such as "stents," "intrasaccular stents," or "flow diverters." It is desirable to avoid expansion and rupture of the aneurysm, and furthermore, it is desirable to avoid clots formed in the aneurysmal sac from migrating and locally blocking the artery.

[0004] Such an implant can be inserted by percutaneous implantation. The implant can be maintained in a radially compressed state in a catheter and deployed after being positioned in the area to be treated. The IMD can be cylindrical, spherical, ellipsoidal, or tubular with a variable radius around its axis of rotation.

[0005] It is important to predict the deployment position that the implant will adopt before implantation. For example, in the case of a "flow diverter", the implant can extend along its longitudinal axis (relative to its length at rest) after the implant is inserted. In the case of an intrasaccular stent or an intra-aneurysm stent with a variable geometry, the implant can extend longitudinally and radially around its rotation axis after it is deployed in the aneurysm sac so that the implant is in close contact with the shape of the aneurysm sac after deployment and has always reached mechanical balance. In order to treat aneurysms, the final length of the implant, its accurate positioning, its diameter, and its juxtaposition against the wall of the artery are many parameters that are important to control. A device that deploys an excessively long length may cover the arterial bifurcation in an undesirable manner. A device that is too short in length may treat aneurysmal pathology in an insufficient manner. In addition, if the juxtaposition of the device against the wall of the artery is not satisfactory, there is a risk of thrombosis.

[0006] Implant insertion following an intravascular route planning is generally performed with the aid of a two-dimensional or three-dimensional image of the artery. Until now, the selection of the IMD reference to be deployed has been based - at least - on local planar measurements (2D) performed by the physician on the patient's imaging. These measurements make it impossible to predict in a reliable way the apposition of the IMD or its final length once it has been deployed.

[0007] In order to take into account the morphology of the vascular structure to estimate the final position of an intravascular implant after deployment, an abacus-based technique is known. The abacus gives the relationship between the length of the device after deployment and its diameter. Assuming that the deployment of the implant is limited by the minimum diameter of the vascular structure surrounding it, an estimate of the length after deployment can be obtained. However, this technique assumes a vascular structure with a constant circular cross-section.

[0008] Therefore, there is a need for a very precise and reliable method for determining the final position of an implant after deployment, in particular its radial expansion after deployment.

[0009] There is also a need for a model that can give an estimate of the apposition of the implant against the wall of the vascular structure. Summary of the invention

[0010] The present invention makes it possible to counteract the aforementioned drawbacks and, according to a first aspect, proposes a method for determining the positioning of a deployable, implantable medical device or IMD at a deployment site, the medical device being intended to be deployed in a vascular structure, the method comprising, from a three-dimensional image of a region of interest including a vascular structure, in which a positioning point of the IMD within the vascular structure has been defined, the following steps:

[0011] Determine the centerline of vascular structures;

[0012] Based on the initial position, position the IMD around the centerline;

[0013] Simulating the final position of the IMD after deployment as the stress exerted on the IMD by the walls of the vascular structure changes,

[0014] Determining the centerline consists in placing points at different longitudinal positions along the vascular structure so as to minimize the travel time of the fluid along said points between an input point in the vascular structure and an output point in the vascular structure, said points forming the centerline, and simulation of the final position of the IMD is performed as the level of longitudinal push and pull intended to be applied to the IMD during implantation of the IMD is varied.

[0015] The present invention has several advantages.

[0016] The invention, which is suitable for simulating implants in humans and in animals, improves the determination of the centerline, a three-dimensional image of the vascular structure being used to determine the points of the centerline. In addition, the use of a gradient descent algorithm makes it possible to obtain a centerline that is closer to physical reality. The centerline so determined is more faithful to the actual longitudinal axis of the implant after deployment.

[0017] This centerline is used as the basis for correcting the position of the IMD to determine the final position of the IMD, particularly its length after deployment.

[0018] Taking into account the level of push-pull during the correction of the position of the IMD makes this correction more reliable, since the mechanical stresses applied during the insertion of the implant are taken into account, for example in the sense of the radial expansion of the implant. The situation in which the implant locally adopts an equilibrium position different from that of a cylinder of rotational shape is then modeled. In fact, for non-zero levels of push-pull, the radial forces applied by the implant bring the wall of the implant and the surface of the vascular structure closer together.

[0019] According to a second aspect, the invention relates to a computer program product comprising code instructions for performing a method such as described above, when said code instructions are executed by processing means of a processing unit.

[0020] According to another aspect, the present invention relates to a processing unit configured to obtain a three-dimensional image of a vessel structure acquired from an acquisition unit and further configured to simulate a final position of a deployable IMD by implementing a method according to, for example, the method described above. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Other characteristics, objects and advantages of the present invention will become apparent from the following description, which is purely illustrative and non-limiting, accompanied by the accompanying drawings, in which:

[0022] Figure 1 Illustrate a system capable of executing the method according to the present invention;

[0023] Figure 2 A sequence of steps of a method for determining a final implant position according to the present invention is illustrated;

[0024] Figure 3a is an angiogram of the artery with the aneurysm;

[0025] Figure 3b corresponds to a three-dimensional view of the same artery, in which the centerline of the artery is represented;

[0026] Figure 3c corresponds to the same three-dimensional view, in which an IMD of the “drainer” type is represented;

[0027] Figure 4a A sequence of steps illustrating a method for determining the position of a "flow diverter" after deployment according to an embodiment is illustrated;

[0028] Figure 4b A sequence of steps illustrating a correction of a geometrical deployment for determining a position of an IMD after deployment;

[0029] Figure 4cA sequence of steps illustrating a correction of mechanical deployment for determining a position of an IMD after deployment;

[0030] Figure 5a , 5b 5c and 5d schematically illustrate the successive iterations within the simulation steps of the final position of the "flow guider" taking into account geometric stresses;

[0031] Figure 6 schematically illustrates a transverse cross section of an artery equipped with an IMD of the "flow guide" type in several possible scenarios;

[0032] Figure 7 A three-dimensional mapping illustrating the degree of juxtaposition provided for an IMD is illustrated.

[0033] Figure 8a illustrates the results of the steps of positioning the IMD in its initial position, Figure 8b The results of the steps of the geometric simulation illustrating the final position of the IMD are illustrated, Figure 8c The results of the steps of the simulation of the mechanical calibration are illustrated. DETAILED DESCRIPTION

[0034] The following description relates to the determination of the final position of an IMD within an artery. However, the invention may be used with equal advantage for any vascular structure of the human or animal body.

[0035] In the following, "implant" or "implantable medical device" (IMD) refers indiscriminately to a deployable implant that is able to adopt a final position within an artery that is different from its initial position (before deployment), but also different from its rest position (deployment in free air) or "nominal position". "Morphological properties of the artery" are taken to mean a set of properties that have a local influence on the final position of the implant (in particular, but not limited to, the minimum diameter, circumference, radius of curvature and spatial derivatives of the implant). Furthermore, a region of interest including the artery to be treated may be a designated "ROI".

[0036] Furthermore, the following description relates specifically to a prosthesis of the "drainer" type, which is essentially cylindrical or tubular in shape. The implant is formed of a mesh made of a material that is biocompatible with human tissue. It is kept in a radially compressed and longitudinally extended position before insertion, for example in a catheter. However, for any type of deployable implant other than a "drainer", for example for an aneurysm stent (intrasaccular device), for a conical shaped device, or a stent-type device (e.g., a "laser-cut stent"), the method according to the invention can be applied with the same advantages.

[0037] System for determining the location of an IMD at a deployed location

[0038] exist Figure 1 In FIG. 2 , a system for determining a location of an IMD according to the present invention comprising a processing unit 20 is shown. The processing unit is, for example, a processor configured to implement the method for determining a location of an IMD to be described below.

[0039] The processing means are advantageously configured to communicate with an acquisition unit 22 configured to acquire views making it possible to reconstruct a three-dimensional image of a region of interest of a patient, said region of interest comprising an artery, and / or with a database DB1 in which three-dimensional images acquired on the patient and / or views making it possible to reconstruct such a three-dimensional image are recorded. The acquisition unit 22 can be, for example, an X-ray imaging system, and said views can be acquired, for example, within the scope of a neuroradiological procedure, such as, for example, the acquisition of a 3D angiography. The processing unit 20 communicates with the acquisition unit 22 and / or the database DB1 via a wired link and / or via a wireless link by means of any suitable network (Internet network, etc.) in order to receive the image Im. In an alternative, the processing unit can extract the image Im from a hard disk or receive the image Im via a storage support playback device (such as a CD reader or a USB port).

[0040] The processing unit is further configured to communicate with a database DB2, which includes data about the implantable medical device or IMD. These data can be, for example, physical IMD characteristics, or pre-recorded IMD models. The data can be supplied by the IMD manufacturer, or determined by analysis or experiment. The link between the processing unit 20 and the database DB2 is achieved by any suitable means.

[0041] Finally, the processing unit 20 may communicate with a display device 21 which supplies a graphical interface for displaying a three-dimensional image of the region of interest and any other display necessary for implementing the method described below. The display device 21 is associated with a user interface for inputting instructions and data.

[0042] Method for determining the location of an IMD at a deployment location

[0043] exist Figure 2 , steps constituting a method 10 of an exemplary embodiment of a method of the present invention for determining a deployment position of an extendable implant within an artery are shown.

[0044] In the following, the body conduit treated by insertion of the implant is an artery and the implant is an intravascular implant; however, the invention can be used with the same advantages for prostheses intended for treating any other body conduit in humans or animals.

[0045] exist Figure 3aIn , a two-dimensional view corresponding to an angiography of an artery 1 to be treated is represented, the artery 1 having an aneurysmal sac in the region A. The image is obtained, for example, by a processing unit connected to an X-ray scanner or by any known means of the same type.

[0046] Prior to the steps of method 10, an initial positioning point D of the implant (referred to as, for example, the "distal point") and, optionally, a second final positioning point P (referred to as, for example, the "near point") are determined. In the case of a flow diverter, these two points may correspond to the positions of the two ends desired by the clinician. An IMD reference is selected automatically or manually by an operator, the reference corresponding to an implant type having a pre-recorded or manually selected size. Method 10 may also provide automatic selection of a suitable implant reference having a suitable size, as a function of information extracted from a three-dimensional image of the artery, and / or as a function of the distance between the near point and the distal point. In the following, it is considered that the selected implant reference corresponds to a "flow diverter". Method 10 furthermore takes as input a three-dimensional image Im of the artery. The protocol for obtaining said three-dimensional image of the artery will not be described in detail here.

[0047] The method 10 comprises a step 300 of determining the centerline C of the artery (at least at the level of the area A). In practice, in order to be able to access the deployment position of the implant, it is advisable to determine the axis along which the implant can be extended or retracted inside the artery. This axis corresponds in its entirety to the centerline of the artery. In step 300, the point C is positioned within the internal volume of the three-dimensional image Im of the artery. i Placed at different longitudinal locations along the artery to determine the centerline C.

[0048] Point C i Placed along the artery in order to obtain the fastest path between an entry point I in the artery (usually the entry point of a microcatheter for performing implantation of the IMD at the level of the region of interest) and an exit point in the artery. The entry point and the exit point may be manually entered by an operator through the interface of the device 21, or may be automatically determined on a three-dimensional image of the artery.

[0049] "Fastest path" is taken to mean the minimization of the travel time of the blood between point I and the output point.

[0050] Advantageously, the step from point I to point C is performed by applying a gradient descent algorithm. i are placed so as to minimize the travel time along the points so placed.

[0051] From point C iThe current point in , finds a point that follows the centerline in the direction opposite to the gradient of the travel time function. The travel time function corresponds to, for example, the distance along the three-dimensional curve arc corresponding to the centerline, multiplied by a cost function with the dimension of the inverse of the speed.

[0052] according to Figure 2 In the specific embodiment shown in FIG. 3 , step 300 includes a sub-step 301 during which the processing unit continuously calculates points C along the artery. i If the artery is a perfect cylinder, then point C i will be placed successively along the axis of rotation of the cylinder, and then form the artery. In reality, arteries are not locally cylindrical. Point C i The positioning is thus achieved by making each point C i The distance between the centerline point C and the adjacent surface of the artery is minimized. i The determination of is also performed by trying to minimize the travel time of the fluid along the determined centerline point. i The connected parts V can be considered in order i Obtained on.

[0053] In sub-step 302, a link point C is drawn on the three-dimensional image of the artery. i Step 302 may include calculating an optimal path between the previously determined point C. i and the center line corresponding to the optimal path. The optimal path may be, for example, the fastest path in the artery between the input of the microcatheter in the artery (point I) and the output point of the artery (point S).

[0054] Finally, in step 303, the processing unit performs a process of extracting a three-dimensional portion V of the artery along the previously determined center line from the three-dimensional image of the artery. i Advantageously, the portion extracted along the centre line corresponds to a segment of the artery which can comprise a tubular shape with a circular cross section.

[0055] Figure 3b is used for Figure 3a A view of a 3D model of artery 1. Figure 3b In the view of FIG. 3 , the centerline 2 obtained for the artery 1 at the end of step 300 is shown. The initial point D for positioning the IMD is also marked. Figure 3b The view corresponds to a three-dimensional representation of the artery that can be provided on the display device 21 during the execution of the method 10 .

[0056] Method 10 then includes a step 400 of inserting an IMD M, which corresponds to the implant reference adopted at the beginning of the method. The distal end of the IMD M is placed at an initial point D (distal point), which is advantageously visible on a three-dimensional image. For example, the distal point D can be positioned on the periphery of the area A to be treated. The IMD M is placed around the center line C determined in step 300. "Surrounding" is taken to mean that the walls of the IMD M surround the center line, even if the IMD is not necessarily centered on the center line. If the IMD M corresponds to a "drainer", the IMD M can be regarded as a tubular shape whose longitudinal axis is consistent with the center line of the artery. Point D constitutes the distal end of the IMD M. The dimensions of the IMD M placed at point D correspond to the dimensions of the implant at rest, which dimensions are not necessarily the same as the dimensions after deployment that will be determined in the remainder of the method.

[0057] These dimensions specific to each reference of IMD M can be selected automatically or manually as a function of the distance between the centerline and the arterial wall determined in step 300 or as a function of the position of point D and neighboring points or as a function of the morphological features of the artery. The reference of IMD M can also be modified as a function of a first estimate of the apposition of the wall of the model M of the IMD against the wall of the artery.

[0058] The initial position of the IMD M at the end of step 400 corresponds to an unstressed position in which the IMD is not stressed in the sense of radial or longitudinal compression exerted by the wall surrounding the artery. In step 500, the position of the IMD M is corrected as a function of the morphological properties of the artery in order to take into account the mechanical stresses exerted by the wall of the artery to obtain the final position after deployment. Advantageously, locally, the length and / or diameter of the IMD M is corrected. Advantageously, the IMD M can be discretized into a set of connected segments in order to perform simulation operations of the final position of the IMD M. Such a situation will be described in detail below with respect to method 40 of FIG. 4.

[0059] After simulating the final position of the IMD D, the position obtained corresponds to the determined position of the IMD after deployment. Its extension can be spontaneous, or on the contrary, it can be caused during the insertion operation of the implant. The final simulated position must therefore enable the operator to notice whether the selected implant reference and the selected initial size are suitable for the treatment of the artery. The operator can especially observe whether the vascular pathology as the target is correctly treated and whether the implant after deployment will not generate undesirable secondary effects on other areas of the vascular tree visible on the three-dimensional image.

[0060] Figure 3c Now, for an implant of the type "drainer", refer to the following steps after executing step 500. Figure 3bwherein represents a three-dimensional representation of the implant IMD M. Figure 3c corresponds to a view provided on a graphical interface connected to the processing unit. Figure 3c In the view of , three implantation zones of the "flow diverter" can be seen: a first zone, in which the implant adopts an overall tubular shape with a slightly varying radius and a slightly deviated centerline 2; a second zone, in which the implant adopts a curved position; and a third zone, in which the implant once again adopts an overall tubular shape. The apposition of the implant is low at the level of the collar of the saccular aneurysm represented here. On the other hand, the implant is correctly apposed on the wall of the artery opposite to the aneurysm. Although Figure 3c If no representation of the degree of apposition of the implant is provided in the view of FIG, such a representation may be provided here, for example, in accordance with the modality described below with respect to method 40.

[0061] exist Figure 4a In the Figure 2 The steps of a method 40 for determining the position of a "flow diverter" type implant after deployment in an artery according to a specific embodiment of the method. The same reference numerals between the figures correspond to similar steps or similar elements. The method can also be performed by Figure 1 The processing unit 20 shown in FIG.

[0062] In step 100, a three-dimensional view Im of the artery to be treated is obtained, for example, by angiography. The three-dimensional image of the artery can be segmented by the "marching cube" method known in the field of image reconstruction. The reconstruction of the three-dimensional image can refer to the following publication: Marching Cube: A high resolution 3D surface construction algorithm, William E. Lorensen, Harvey E. Cline, Computer Graphics, 1987.

[0063] In step 200, an area A is marked manually by the operator or automatically on the three-dimensional view obtained at the end of step 100. This area A corresponds to the artery treated by the insertion of the implant and may in particular correspond to an aneurysmal pathology of the saccular or fusiform type, or any other type of aneurysmal pathology, or a localized constriction, or a stenosis, or a thrombosis of the artery.

[0064] In an optional step 250, the three-dimensional image Im is verified. In particular, the quality of the image Im can be verified by thresholding: the three-dimensional image Im is superimposed on the two-dimensional radiographic view at the same angle at which the thresholding is applied. The three-dimensional image can be corrected as a function of the result of the comparison with the two-dimensional thresholded image, in particular the size of the arterial tree can be verified. The three-dimensional image Im can also be rescaled relative to the two-dimensional radiography.

[0065] It should be noted that steps 100 to 250 are optional for performing the method 40. The method 40 may be performed by a processing unit receiving as input a three-dimensional image of the artery to be treated having the region A.

[0066] In step 300, the processing means determines the centerline C of the artery. The centerline thus obtained intersects the area to be treated. Figure 2 The method 10 describes the modal method to determine the centerline.

[0067] In the optional step (in Figure 2 From the three-dimensional image of the artery and the centerline determined in step 300, the processing unit can (if necessary) perform corrections of anastomoses that do not exist on the real artery to be treated, such as artery-artery fusion or artery-aneurysm sac fusion. Such errors may occur during reconstruction and can also be corrected by the operator.

[0068] At step 400, an IMD M corresponding to a preselected reference of a "flow diverter" having dimensions at rest is positioned at an initial point D in a manner similar to step 400 of method 10. The IMD M is advantageously selected to have a tubular shape with a cross section of constant radius along and centered on the center line C determined at step 300. The IMD M according to this initial positioning may extend beyond the wall of the artery in certain areas.

[0069] In step 410, the IMD M is discretized into a plurality of segments M. j , where index j is the index of a connected segment of IMD M. Advantageously, the segments M of the discretized model j Each of the segments M is approximated by the processing means with a volume of cylindrical shape. If the IMD M obtained at the end of step 400 is tubular with a cross section of constant radius, then all segments M jAll correspond to tubes of the same radius centered on the centerline C. The number of segments may be predetermined, independent of the morphological properties of the artery, and may be fixed, for example, to 200. The length of all segments may be the same, and taken to be equal to the length of the centerline divided by the number of segments. In an alternative, the length of each of the segments may not be chosen uniformly. For example, the length of the segments may be chosen in such a way that a finer meshing is obtained on regions where the circumference of the wall of the artery is highly variable, or rather on regions where the centerline is highly deviated. The discretization of IMD M may be performed from the initial point D, and therefore from one end of the initial position of IMD D all the way to the other end.

[0070] The model discretized into segments obtained at the end of step 410 is used to perform a simulation of the final position of the IMD M. This simulation is performed by taking into account the stresses, either geometrical, mechanical or both, exerted on the IMD M by the wall of the artery. The goal of taking into account these stresses is to obtain a simulated final position corresponding to the position of the implant after its deployment inside the artery. The fact of initially taking into account only the geometrical stresses exerted by the wall (without seeking a mechanical equilibrium at the level of the wall of the IMD) makes it possible to save computational time, taking into account the simulation time of the mechanical correction in general.

[0071] and Figure 4b Relatedly, the steps of simulating the final position according to the embodiment 500 in the first case of considering geometric stress will be described here.

[0072] In step 500, for each segment M, while taking into account the variation in the inner radius of the artery, j The length and diameter of the implant are corrected. As mentioned above, each segment can be approximated by a tubular volume. For each of these segments, a behavior law of the IMD that mechanically links length and diameter is applied, the law being, for example, related to a preselected implant reference. The behavior law can be linear or improved or nonlinear, and can be determined experimentally, or derived by previous analytical development, or otherwise supplied in a database, for example if it is supplied by the manufacturer of the implant. In the case where the implant is longitudinally stretched, radially retracted, and if longitudinally compressed, it radially widens, the slope obtained as a function of diameter for improving the approximation of length can be negative.

[0073] The step 500 of correcting the position of the "flow guider" IMD M may be performed iteratively as follows.

[0074] For segment M in order j For each of , steps 501 and 502 are iterated one by one.

[0075] In sub-step 501, a segment M is retrieved from a memory stored in a database accessible to a processing unit. j Current position, modify segment M j Diameter of segment M j Diameter D j The modification is to change segment M j Accommodated in the surrounding segment M of the artery j The area of ​​the smallest diameter of the segment is performed in such a way that the segment M j The wall touches the area of ​​minimum diameter. The behavior law given by segment M can be considered j If the minimum diameter of the portion of the artery is greater than the maximum diameter, then the diameter D j It is then modified to be equal to the maximum diameter.

[0076] Next, in sub-step 502, by means of the behavior law of the IMD and the segment M in step 501, j The corrected diameter value is used for segment M j Length L j For example, if segment M is radially retracted during step 501 j , then in step 502, stretching segment M j .

[0077] These steps 501 and 502 are repeated for each of the segments for iterating step 500 .

[0078] In sub-step 503, by j The corrected length L j The sum is performed to determine the total length L of IMD M.

[0079] At the end of the determination of the geometrical position, it may be necessary to correct the position of the IMD by starting from the final known position of the IMD (either the position obtained from step 400 or the position obtained from step 500), if the mechanical balance is not sufficiently satisfactory. The processing unit may perform a simulation of the final position of the IMD M according to a second alternative in which the mechanical balance is sought for a simulated wall of the IMD M. This second mode corresponds to the embodiment 800 of the step of simulating the final position of the IMD M.

[0080] Figure 4c The sub-steps of this embodiment are described in detail in .

[0081] In sub-step 801 , a mechanical modeling of the IMD is proposed based on, for example, a finite element method considering the mechanical links between different segments of the IMD in a mechanically stress-free configuration of the IMD.

[0082] In sub-step 802, from the stress-free state read in database BD2, segment M at the last known position is j For each segment M j , applying a geometric transformation between the configuration without mechanical stress (position of the IMD at rest) and the starting configuration for mechanical correction:

[0083] - either from step 400 of positioning the IMD according to the initial position,

[0084] - Either from step 500 of geometrical simulation of the final position of the IMD.

[0085] In sub-step 803, the processing unit performs the following operations on each segment M: j Mechanical modeling of the contact with the surface of artery 1 is defined.

[0086] Finally, in sub-step 804, a nonlinear calculation of the mechanical balance of the walls of the IMD M is performed, if necessary, applying the segment M of the IMD. j The final simulated position reached corresponds to the position thus calculated, in which the wall of the IMD reaches mechanical equilibrium.

[0087] Figure 5a The example of artery 1 is schematically illustrated, during the first iteration of steps 501 to 503, segment M j The diameter and length of the segment M are modified, where the index j ranges from 1 to n=6. j The position before correction is a solid line, and the correction position M' j It can be observed that the segments whose lengths and diameters are corrected to take into account the morphological properties of the artery are no longer necessarily connected to each other.

[0088] Next, in sub-step 504, the length obtained for the IMD in step 503 is compared with the length obtained in the previous iteration of steps 501 to 503. If the difference in the total length L obtained is sufficiently close to zero (convergence criterion: absolute value of the difference between the lengths), the iteration loop is exited and the length L of the segment is set to j The length of the segment of the implant whose final position has been simulated is determined. For example, the absolute value of the difference is compared with a predetermined threshold value.

[0089] If, on the other hand, the total length L is determined to be sufficiently close to the previous total length, a new iteration of steps 501 to 503 is performed. In order to prepare for this new iteration while taking into account the modifications made to the lengths and diameters of the segments, the positions of the segments are adjusted so that they are connected again, for example from the initial point D. This is done in Figure 5b is visible in the Figure 5aThe same example is used for the next iteration of steps 501 to 503. The solid line corresponds to the position of the segment before performing sub-steps 501 and 502 for said iteration: It should be noted that the length and diameter of the segment actually correspond to Figure 5a The correction position of segment M j The fact that the segments have been repositioned one by one can once again cause a mismatch between the diameter of the segment and the wall surrounding the artery 1 and lead to a new re-sizing of the segment.

[0090] In this regard, Figure 5c and 5d In the figure, for the same segment, Figure 5a and 5b Those iterations of are connected to two iterations. Figure 5d At the end of the iteration represented in , the final length L of the implant is determined as the sum of the lengths of the corresponding segments. Upon exiting the loop of step 500, the segments are repositioned one by one and the simulated position of the IMD M after the implant is deployed is obtained. Once deployed, the final length of the implant is thus taken to be equal to the length L of the segment at this simulated position. j sum.

[0091] The discretization method described above in connection with steps 400 to 500 is applicable to any type of pathology of the artery. It makes it possible to have a very close to realistic prediction of the final length of the implant after deployment, and thus can guide the clinician's choice. The discretization proposed here is advantageous because at a given iteration, the corrected length of each of the segments of the model is taken into account for the next iteration.

[0092] According to an alternative embodiment of method 40, the position of IMD M is corrected in step 500 not only taking into account the morphological characteristics of the artery, such as the circumference of the artery near the segment, but also taking into account the level of push and pull applied by the practitioner during the insertion of the implant. In fact, if a certain stress is applied to the implant during insertion, for example, in the sense of longitudinal compression that produces radial extension, the implant can locally take a circumference that exceeds the circumference of a circle inscribed in the wall of the artery. The implant can take a local non-tubular shape (with a non-circular radial cross-section). In particular, stress in the longitudinal sense can be spontaneously applied during implant placement to extend the implant radially and force it to be juxtaposed against the wall of the artery, for example, in an area where the wall does not have a circular cross-section.

[0093] For example, as a "flow diverter" segment, the corrected diameter of the segment may be determined as a function of the circumference of the walls surrounding the artery (which may tend to compress the segment radially) by also taking into account the longitudinal compression applied during implantation (which may tend to radially extend the segment). To take into account the level of push and pull, the segment M at step 501 may be weighted by assigning a weight to the effect of the circumference of the surrounding artery. j Calculation of the corrected diameter.

[0094] It will be readily appreciated that the other modalities for performing step 500 described above are still applicable in this case.

[0095] Figure 6 The simulated influence of the level of push and pull on the position of the implant after deployment is illustrated in the schematic diagram of . On a non-circular cross section of the wall of the artery 1 , a "flow guider" IMD M with a cylindrical shape without stress is represented.

[0096] exist Figure 6 , it can be observed that the selected IMD M has a radius that is too small at rest to be properly apposed against the wall of the artery 1.

[0097] For Figure 6 The same implant visible in the middle view of (corresponding to the absence of longitudinal compression), the IMD M is radially extended, with the result that its diameter, in the represented section, approximately reaches the minimum diameter of the wall of the artery 1. However, the artery is not locally circular, and areas of the artery still exist for which the wall of the implant model is not correctly apposed to the wall of the artery 1.

[0098] Finally, for Figure 6 The same implant visible in the bottom view of , with an important longitudinal compression, the radial expansion of the wall of the IMD M is sufficient to obtain a general apposition of the implant against the wall of the artery, by making here a completely rigid prosthesis of the artery. In addition, the longitudinal compression is sufficient to impose a local non-circular shape on the implant after the expansion. In reality, the surface of the artery is not rigid, and the radial forces exerted by the wall of the implant in the case of non-zero longitudinal compression can produce deformations of both the wall of the implant and the surface of the artery. The application of "push / pull" during the insertion of the implant therefore makes it possible to obtain a good apposition of the implant against the wall of the artery for an implant of the "drainer" type, especially in areas where the artery is locally non-circular. The alternative to the above-mentioned step 500 makes it possible to take into account the possibility of applying "push / pull", thus making it possible to make the simulation of the implant reliable.

[0099] Optionally and advantageously, at the end of the determination of the corrected position of the IMD M corresponding to the simulated position of the implant, Figure 4aAs represented in , an additional step 600 of determining the degree of apposition of the implant is performed.

[0100] Once the position of the implant IMD M after deployment has been simulated, the processing unit can calculate the degree of apposition as the proportion of the surface of the implant on which the wall of the implant is well apposed against the wall of the artery. Figure 6 In the case described, the top view corresponds to a degree of apposition of 0% and the bottom view corresponds to a degree of apposition of 100%. It will be readily understood that, in the case of aneurysmal sac type pathology, and for an implant of the "flow diverter" type, it is not desirable to obtain a good apposition of the wall of the implant against the wall of the aneurysmal sac; on the other hand, it is desirable to obtain a good apposition of the device against other areas of the artery.

[0101] For IMDs that are not likely to be "flow diverters" (such as, for example, stents within aneurysms), apposition can be determined by considering the mechanical contact forces exerted by the wall of the artery on the wall of the implant, or rather by considering the distance between the nodes of the wall of the IMD and the adjacent wall of the artery (the IMD is considered to be properly apposed below a certain distance threshold).

[0102] Optionally, method 40 may include an additional step 700 of determining the porosity of the walls of the IMD M. This step may alternatively be performed before step 600 of determining the degree of juxtaposition of the walls of the IMD. The determination of the porosity of the walls of the IMD M is performed according to any known method in the prior art.

[0103] At the end of determining the degree of apposition for IMD M, independently of the execution of step 700 of determining the porosity of the wall of the IMD, the processing unit can display via the display device 21 a three-dimensional view of the artery treated with the simulated three-dimensional position of the implant, and further display a mapping of the degree of apposition over the entire surface of the implant. Figure 7 Such a view is schematically shown in Figure 7 In FIG. 1 , artery 1 treated with a “flow guide” can be seen at the level of zone A along centerline C. For zones 30 and 32 , the apposition of the implant against the wall of artery 1 is more important than at the level of the collar of the aneurysm at zone 31 .

[0104] At the end of the method 40 iterations for determining the positioning of the IMD at the deployed position, if the determined final position is not close enough to the wall of the artery (e.g., if the final apposition is deemed insufficient), a new IMD model may be provided to better approximate the wall of the artery. j If the minimum diameter of the portion of the artery is greater than the maximum diameter, then the diameter D j It is then modified so as to be equal to the maximum diameter.

[0105] In the alternative, steps 400 and 500 such as described above may be iterated repeatedly using different implant references having, for example, different nominal diameters. Comparison of several final positions of the IMD obtained for different implant references by possibly varying the positioning of the distal point D and / or the proximal point P allows the clinician to select the implant reference and the modality of intervention that is most suitable for the treatment of the pathology that the artery has.

[0106] Figure 8a The result of the step of positioning the IMD in its initial position for an intra-aneurysm stent type is illustrated. At the end of step 400, this type of implant has been positioned in the three-dimensional image of the artery 1 according to the initial position M0 along the center line 2 calculated, for example, according to step 300 described above.

[0107] Figure 8b The visible result on the graphical interface at the end of the iteration of step 500 of simulating the final position of the IMD while uniquely taking into account the geometric stresses exerted by the inner wall of the capsule is represented. The position M1 of the IMD is thus obtained.

[0108] Finally, in Figure 8c , the visible result on the graphical interface is represented at the end of an iteration of step 800 of simulating the final position of the IMD by trying to solve the mechanical balance for the walls of the IMD according to the previously determined position M1 , taking into account the mechanical stresses exerted by the walls.

[0109] For this example, much more computing time would have been required to calculate the mechanical balance according to step 800 from the initial position M0 than would have been required here to calculate the position M2 from the geometric stresses exerted by the inner wall of the capsule for the position M1 for which this has been taken into account.

Claims

1. A method for determining the positioning of a deployable, implantable medical device (IMD) at a deployment site, the medical device being intended to be deployed in a vascular structure (1), the method comprising: based on a three-dimensional image of a region of interest including the vascular structure, in which a positioning point (D) of the IMD has been defined, comprising executing the following steps by means of a computer: - determining a centerline (C) of the artery, determining the centerline (C) comprises placing points at different longitudinal positions along the vascular structure so that the flow of fluid along the points (C) between an input point (I) in the vascular structure and an output point (S) in the vascular structure is i ) is minimized, said points forming said center line (C); - positioning said IMD (M) around said centre line (C) according to the initial position, said IMD being deployed along said centre line (C) and centered on said centre line (C); - simulating a final position (M) of the IMD after deployment as a function of the stress exerted on the IMD by the wall of the vascular structure (1), the simulation of the final position of the IMD being performed as a function of the level of longitudinal push and pull intended to be exerted on the IMD during implantation of the IMD, - determining the degree of apposition of the IMD on the wall of the vascular structure in the final position to estimate the apposition of the implant to the wall of the vascular structure, the degree of apposition being the proportion of the surface of the IMD of the implant on which the wall of the implant is well apposed against the wall of the artery, The final position and degree of apposition enables selection of an IMD that matches the vascular architecture.

2. The method according to claim 1, wherein: By using the gradient descent algorithm to place the points (C i ) are minimized, the points forming the center line (C).

3. The method according to claim 1, wherein: The determining of the center line (C) comprises sub-steps, wherein the sub-steps include: - Draw a line through the point (C i )’s center line (C); - discretizing the vascular structure so as to obtain a sequence of three-dimensional sections of the vascular structure along the centerline.

4. The method of claim 1, wherein the step of locating the IMD according to the initial position is followed by discretizing the IMD into a set of longitudinal three-dimensional segments, The step of simulating the final position takes into account the geometric stresses exerted by the walls of the vascular structure on the IMD by the following sub-steps: a) For each segment (M j ), modifying the diameter of the segment as a function of the circumference of the vascular structure in the vicinity of the segment, and modifying the length of the segment by means of a behavior law of the IMD linking the length to the diameter of the segment; b) calculating the length of the IMD as the sum of the lengths of the segments at the end of step a); c) comparing the two final lengths calculated in step b), where - if the absolute value of the difference between the two calculated final lengths of the IMD is below a threshold value, the length of the IMD in the final position is the final length calculated in step b), and - If the absolute value of the difference is above the threshold, the correction step comprises a step of adjusting the position of each segment of the IMD taking into account the modification of the length of the segment at the end of step a), and repeating steps a) to c) with the segment thus modified.

5. The method according to claim 4, wherein: If the final position determined for the IMD is not close enough to the wall of the vascular structure, a segment with a larger diameter (M j ) to repeatedly perform the step of simulating the final position so as to bring the segments of the wall of the vascular structure closer together.

6. The method according to claim 4, wherein: The behavior law is dependent on the relationship between geometrical and mechanical parameters of the IMD.

7. The method according to claim 1, wherein: The step of simulating the final position takes into account the mechanical stress exerted by the wall of the vascular structure on the IMD through the following sub-steps: - Assign mechanical modeling to each segment (M j ); - For each segment (M j ), transform the diameter of the segment (D j ), and in the segment (M j ) and the vascular structure (1); - Solving the mechanical balance of the IMD to obtain the final position of the IMD.

8. The method according to claim 1, comprising a preliminary step of verifying the 3D reconstruction of the surface of the vascular structure in the region of interest, said verification being performed by thresholding.

9. The method of claim 1, comprising, after the step of determining the centerline, the step of correcting one or more non-physiological anastomoses of the surfaces, such as artery-artery fusion or artery-aneurysm sac fusion.

10. The method according to claim 1, comprising the additional step of three-dimensional graphical representation of the vessel structure in the region of interest including a determined centerline (C) and an optional degree of apposition.

11. The method according to claim 1, wherein: The IMD is a flow diverter, or an intra-aneurysm stent, or a laser-cut stent type.

12. The method of claim 1, comprising the step of determining the porosity of the walls of the IMD in a final position.

13. Computer program product comprising code instructions for performing the method according to claim 1 when the code instructions are executed by processing means of a processing unit.

14. A processing unit (20), the processing unit (20) being configured to obtain a three-dimensional blood vessel structure image acquired from an acquisition unit (22), and further configured to simulate a final position of a deployable IMD by implementing the method according to claim 1.

Images