Method for determining the positioning in deployed position of an implantable medical device after expansion in a vascular structure

Abstract

The invention relates to a method for determining the deployed position of an implant in the form of an expandable medical device, which method, starting from a three-dimensional image of a region of interest comprising the vascular structure, comprises the following steps: determining a central line of the vascular structure, positioning the IMD in an initial position around the central line, simulating the final position of the IMD after deployment, depending on the stresses exerted on the IMD by the walls of the vascular structure, the determination of the central line consisting in placing points in such a way as to minimize a fluid transit time along said points between an inlet point and an outlet point, the transit time being minimized by using a gradient descent algorithm, the simulation of the final position of the IMD taking into account a rate of longitudinal compression intended to be applied to the IMD during the implantation of the latter. Figure 2

Description

[0001] Method for determining the deployed position of an implantable medical device after expansion within a vascular structure

[0002] TECHNICAL FIELD OF THE INVENTION AND STATE OF THE ART

[0003] The present invention falls within the field of numerical simulation of vascular implants, before or during the implantation operation.

[0004] More specifically, the invention relates to predicting the mechanical behavior of an implantable medical device (IMD), for which a three-dimensional map of a vascular structure, such as an artery, undergoing local pathology like an aneurysm, is available prior to endovascular placement of said implant. This prediction is useful to the clinician for choosing an optimal size and initial positioning of the device, or even for selecting an optimal model, during the procedure.

[0005] It is common to use an expandable implantable medical device (IMD), such as a stent, intrasaccular cage, or flow diverter (according to the commonly used Anglo-Saxon terminology), to treat, for example, an artery affected by an aneurysm. The aim is to prevent the aneurysm from expanding and rupturing, and also to prevent clots formed in the aneurysmal sac from migrating and locally blocking an artery.

[0006] Such an implant can be placed percutaneously. The implant can be stored in a radially compressed state within a catheter and deployed after positioning in the treatment area. The implant can be cylindrical, spherical, ellipsoidal, or tubular with a variable radius around its axis of revolution.

[0007] It is important to predict the implant's deployed position before placement. For example, in the case of a flow diverter, the implant may extend (relative to its resting length) along its longitudinal axis after placement. In the case of a variable-geometry intrasaccular or intraaneurysmal cage, the implant may extend longitudinally and radially around its axis of revolution after deployment within the aneurysmal sac, so that after expansion, the implant conforms to the shape of the aneurysmal sac until mechanical equilibrium is achieved. For aneurysm treatment, the final length of the implant, its precise positioning, its diameter, and its apposition against the arterial walls are all parameters that must be carefully controlled. A device that deploys to an excessive length may unintentionally cover an arterial bifurcation.A device that is too short may inadequately treat the aneurysmal pathology. Furthermore, if the device is not properly positioned against the artery walls, there is a risk of thrombus formation.

[0008] Planning for endovascular implant placement is generally performed using two-dimensional or three-dimensional images of the artery. To date, the selection of the implantable medical device (IMD) reference to be deployed is based—at a minimum—on local planar (2D) measurements taken by the physician on the patient's imaging. These measurements do not allow for reliable prediction of IMD apposition or its final length once deployed.

[0009] To account for the morphology of the vascular structure when estimating the final position of an endovascular implant after deployment, techniques based on the use of nomograms are available. These nomograms establish a relationship between the length of the device after deployment and its diameter. Assuming that the implant's expansion is limited by the minimum diameter of the surrounding vascular structure, it is possible to obtain an estimate of the length after deployment. However, this technique presupposes a vascular structure with a constant circular cross-section.

[0010] Therefore, there is a need for a highly accurate and reliable method to determine the final position of an implant after deployment, and in particular its radial expansion after deployment. There is also a need for a model capable of estimating the implant's apposition against the walls of the vascular structure.

[0011] GENERAL PRESENTATION OF THE INVENTION

[0012] The invention makes it possible to overcome the aforementioned drawbacks and proposes, according to a first aspect, a method for determining the positioning in deployed position of an expandable implantable medical device, or IMD, said 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 the vascular structure in which a positioning point of the IMD within the vascular structure has been defined, the following steps:

[0013] determination of a central line of the vascular structure,

[0014] positioning of the DMI according to an initial position, around the central line,

[0015] simulation of the final position of the DMI after deployment, as a function of constraints exerted by the walls of the vascular structure on the DMI, the determination of the centerline consisting of placing points at different longitudinal positions along the vascular structure, so as to minimize the fluid travel time along said points between an entry point into the vascular structure and an exit point of the vascular structure,

[0016] with travel time minimized using a gradient descent algorithm, these points forming the centerline,

[0017] and the simulation of the final position of the DMI being carried out as a function of a longitudinal compression rate intended to be applied to the DMI during its implantation.

[0018] The invention has numerous advantages.

[0019] The invention, applicable to the simulation of an implant in both humans and animals, improves the determination of the centerline. A three-dimensional image of the vascular structure is used to determine the centerline points. Furthermore, the use of a gradient descent algorithm yields a centerline that more closely reflects physical reality. The resulting centerline more accurately represents the actual longitudinal axis of the implant after deployment.

[0020] This central line serves as a basis for correcting the position of the DMI, to determine a final position of the DMI, and in particular its length after deployment.

[0021] Taking into account a longitudinal compression ratio when correcting the position of the implantable medical device (IMD) makes this correction more reliable, as it considers the mechanical stress exerted during implant placement, which could, for example, lead to radial expansion of the implant. This modeling then considers cases where the implant locally adopts an equilibrium position other than a cylindrical shape. Indeed, for a non-zero longitudinal compression ratio, the radial force exerted by the implant brings the implant walls and the surface of the vascular structure closer together.

[0022] Additional and non-limiting features of a method according to the first aspect of the invention are those defined in each of claims 2 to 12, taken alone or in any of their technically possible combinations.

[0023] According to a second aspect, the invention relates to a computer program product comprising code instructions for the execution of a process as described above, when executed by processing means of a processing unit.

[0024] According to another aspect, the invention relates to a processing unit configured to obtain a three-dimensional image of vascular structure acquired from an acquisition unit, and further configured to simulate a final position of an expandable DMI, by implementing a method as described above.

[0025] GENERAL PRESENTATION OF THE FIGURES

[0026] Other features, purposes and advantages of the invention will become apparent from the following description, which is purely illustrative and not limiting, accompanied by the attached drawings, among which:

[0027] Figure 1 illustrates a system suitable for carrying out a process according to the invention;

[0028] Figure 2 illustrates a sequence of steps of a method for determining the final position of an implant according to the invention;

[0029] Figure 3a is an angiogram of an artery affected by an aneurysm;

[0030] Figure 3b corresponds to a three-dimensional view of the same artery, in which the central line of the artery has been represented;

[0031] Figure 3c corresponds to the same three-dimensional view in which a "flow diverter" type DMI has been represented;

[0032] Figure 4a illustrates a sequence of steps of a process according to one embodiment, for determining the position of a "flow diverter" after deployment;

[0033] Figure 4b illustrates a sequence of steps for a geometric deployment correction, for determining the position of a DMI after deployment;

[0034] Figure 4c illustrates a sequence of steps for a mechanical deployment correction, for determining the position of a DMI after deployment;

[0035] Figures 5a, 5b, 5c and 5d schematically illustrate successive iterations within a final position simulation step of a "flow diverter" taking into account geometric constraints; Figure 6 schematically illustrates cross-sections of an artery equipped with a "flow diverter" type DMI, in several possible cases;

[0036] Figure 7 illustrates a three-dimensional map of the degree of apposition expected for a DMI.

[0037] Figure 8a illustrates the result of the DMI positioning step in its initial position, Figure 8b illustrates the result of the geometric simulation step of the final position of the DMI, and Figure 8c illustrates the result of the simulation step of a mechanical correction.

[0038] DETAILED DESCRIPTION OF IMPLEMENTATION METHODS

[0039] The following description relates to determining the final position of a DMI within an artery. However, the invention can be used with the same advantages for any vascular structure in the human or animal body.

[0040] Throughout this document, the terms "implant" and "implantable medical device" (IMD) will be used interchangeably to refer to an expandable implant that can assume a final position within an artery different from its initial position (before deployment) and also different from its resting position (deployment in open air) or "nominal position." "Morphological characteristics of the artery" refers to a set of characteristics that locally influence the final position of the implant (including, but not limited to, minimum diameter, circumference, radii of curvature, and their spatial derivatives). Furthermore, a region of interest, including the artery to be treated, may be designated as the "ROI."

[0041] Furthermore, the following description specifically relates to a flow diverter-type prosthesis, substantially cylindrical or tubular in shape. This implant is made of a mesh of biocompatible material for human tissues. It is held in a radially compressed and longitudinally elongated position, for example, within a catheter, prior to insertion. However, a method according to the invention can be applied with the same advantages to any type of expandable implant other than a flow diverter, for example, an intra-aneurysmal cage (intrasaccular device), a conical device, or a stent-type device, for example, a laser-cut stent, according to common Anglo-Saxon terminology.

[0042] System for determining the deployed position of a PMI

[0043] Figure 1 shows a system for determining the positioning of a DMI comprising a processing unit 20 according to the invention. This processing unit is, for example, a processor configured to implement a method for determining the positioning of a DMI, which will be described below.

[0044] The processing means are advantageously configured to communicate with an acquisition unit 22, configured to acquire views for reconstructing a three-dimensional image of a patient's region of interest, said region of interest including an artery, and / or to communicate with a database DB1 in which three-dimensional images acquired from a patient and / or views for reconstructing such three-dimensional images are stored. The acquisition unit 22 may, for example, be an X-ray imaging system, and the views may, for example, be acquired as part of a neuroradiology procedure such as 3D angiography. The processing unit 20 communicates with the acquisition unit 22 and / or with the database DB1 to receive Im images, via wired and / or wireless connection using any suitable network (Internet network, etc.).Alternatively, the processing unit can extract the Im images from a hard drive or receive them via a storage media reader such as a CD drive or USB port. The processing means are further configured to communicate with a DB2 database containing data on implantable medical devices (IMDs). This data may include, for example, physical characteristics of IMDs or pre-registered IMD models. This data may be provided by IMD manufacturers or determined analytically or experimentally. The connection between the processing unit 20 and the DB2 database is established by any suitable means.

[0045] Finally, the processing unit 20 can communicate with a display device 21, providing a graphical interface for displaying three-dimensional images of regions of interest and for any other display necessary for implementing the process described below. The display device 21 is associated with a user interface for entering instructions and data.

[0046] Method for determining the deployed position of a DMI

[0047] Figure 2 shows steps of a method 10, which is an example of implementing a method of the invention for determining the deployed position of an extensible implant within an artery.

[0048] In what follows, the body conduit treated by the placement of an implant is an artery, and the implant is an endovascular implant; however, the invention could be used with the same advantages for a prosthesis intended for the treatment of any other body conduit, in humans or animals.

[0049] Figure 3a shows a two-dimensional view corresponding to an angiography of an artery 1 to be treated, showing an aneurysmal sac in area A.

[0050] This image is obtained, for example, by a processing unit connected to an X-ray scanner or by any similar known means. Prior to the steps of procedure 10, an initial positioning point D of the implant, called, for example, the "distal point," is determined, and optionally, a second final positioning point P, called, for example, the "proximal point." In the case of a flow diverter, these two points can correspond to the positions of the two ends desired by the clinician. A DMI reference is selected, either automatically or manually by an operator; this reference corresponds to an implant type with pre-recorded or manually selected dimensions.Method 10 can also automatically select a suitable implant reference with appropriate dimensions, based on information extracted from the three-dimensional image of the artery, and / or based on the distance between the proximal and distal points. In the following, the selected implant reference is considered to be a "flow diverter." Method 10 also takes as input a three-dimensional image Im of the artery. We will not detail the protocol for obtaining this three-dimensional artery image here.

[0051] The method 10 includes a step 300 for determining a centerline C of the artery, at least in area A. Indeed, to access the deployed position of the implant, it is necessary to determine the axis along which the implant can extend or retract within the artery. This axis corresponds roughly to the centerline of the artery. The centerline C is determined in step 300 by placing points C, at different longitudinal positions along the artery, within the internal volume of the three-dimensional image Im of the artery.

[0052] Points Ci are positioned along the artery to obtain the fastest possible path between an entry point I in the artery—typically the entry point of a microcatheter for implanting the DMI in the region of interest—and an exit point of the artery. The entry and exit points can be entered manually by an operator via the device interface 21, or can be automatically determined from the three-dimensional image of the artery. "Fastest path" refers to minimizing the travel time for blood between point I and the exit point.

[0053] In a very advantageous way, the placement of points Ci from point I is carried out by applying a gradient descent algorithm, to minimize the travel time along the points thus placed.

[0054] Starting from a current point among the points Ci, we search for the next point on the central line in the direction opposite to the gradient of the travel time function.

[0055] The travel time function corresponds, for example, to a distance along a three-dimensional curve arc corresponding to the centerline, multiplied by a cost function having the dimension of the inverse of a speed.

[0056] According to a particular embodiment shown in Figure 2, step 300 includes a substep 301 during which the processing unit successively calculates points C along the artery. If the artery were perfectly cylindrical, the points C would be placed successively along the axis of revolution of the cylinder forming the artery. In reality, the artery is not locally cylindrical. The positioning of the points C is therefore carried out by minimizing the distance between each point C and the surrounding surface of the artery. Furthermore, the determination of a centerline point C is also carried out by minimizing the fluid travel time along the already determined centerline points. The points C can be obtained on consecutive segments V considered sequentially.

[0057] In substep 302, the central line C, connecting points C, is drawn on the three-dimensional image of the artery. Step 302 may include calculating the optimal path between previously determined points C, and the central line then corresponds to this optimal path. The optimal path may, for example, be the fastest path within the artery between the microcatheter's entry point into the artery (point I) and the artery's exit point (point S). Finally, in step 303, the processing unit extracts three-dimensional portions V of the artery from the three-dimensional image, along the previously determined central line. Advantageously, the portions extracted along the central line correspond to arterial segments, which may have a tubular shape with a circular cross-section.

[0058] Figure 3b is a view of a three-dimensional model for artery 1 of Figure 3a. In the view of Figure 3b, the centerline 2 obtained for artery 1 at the end of step 300 is shown. The initial point D for positioning a DMI is also marked. The view in Figure 3b corresponds to a three-dimensional representation of the artery that can be displayed on the display device 21 during the execution of process 10.

[0059] The procedure 10 then includes a step 400 of placing a DMI M, corresponding to the implant reference taken at the start of the procedure. The distal end of the DMI M is placed at the initial point D (distal point), which is advantageously visible on the three-dimensional image. For example, the distal point D can be positioned at the periphery of the area A to be treated. The DMI M is placed around the centerline C determined in step 300. By "around" is meant that the walls of the DMI M surround the centerline, even if the DMI is not necessarily centered on the centerline. If the DMI M corresponds to a "flow diverter," the DMI M can be tubular in shape with its longitudinal axis coinciding with the centerline of the artery. Point D constitutes the distal end of the DMI M.The dimensions of the DMI M placed at point D correspond to the dimensions of the implant at rest, which are not necessarily identical to the dimensions after deployment which will be determined following the process.

[0060] These dimensions, specific to each DMI M reference, can be selected automatically based on the positions of point D and the proximal point, the distance between the centerline determined in step 300 and the artery walls, or based on the artery's morphological characteristics, or manually. The DMI M reference can also be modified based on an initial estimate of the apposition of the DMI model M walls against the artery walls.

[0061] The initial position of the DMI M at the end of step 400 corresponds to a stress-free position, where the DMI is not subjected to radial or longitudinal compression by the surrounding artery walls. In step 500, the position of the DMI M is corrected according to the morphological characteristics of the artery, so as to take into account the mechanical stresses exerted by the artery walls to obtain a final position after deployment. Advantageously, the length and / or diameter of the DMI M are corrected locally. Advantageously, the DMI M can be discretized into a set of connected segments to perform the simulation of the final position of the DMI M. Such a case will be detailed below in relation to method 40 of Figure 4.

[0062] After simulating the final position of the M-shaped implantable device (IMD), the resulting position corresponds to the determined position of the IMD after deployment. Its extension can be spontaneous or induced during the implant placement procedure. The simulated final position should therefore allow an operator to determine whether the chosen implant reference and initial size are suitable for treating the artery. This may involve observing whether the targeted vascular pathology is being treated correctly and whether the implant, after expansion, would produce undesirable side effects on other areas of the vascular tree visible in the three-dimensional image.

[0063] Figure 3c reproduces the three-dimensional representation of Figure 3b, which shows the implant's M-shaped design after the implementation of step 500 for a flow diverter-type implant. Figure 3c corresponds to a view provided on a graphical interface connected to the processing unit. Three implantation zones of the flow diverter are visible in Figure 3c: a first zone where the implant adopts a generally tubular shape with a slightly variable radius and a slightly deviated central line 2; a second zone where the implant adopts an angled position; and a third zone where the implant again adopts a generally tubular shape. The implant apposition is weaker at the neck of the saccular aneurysm shown here. Conversely, the implant is correctly apposed on the arterial wall opposite the aneurysm.Although a representation of the degree of implant apposition is not provided in the view of Figure 3c, such a representation could be provided here, for example according to the modalities which will be described below in relation to method 40.

[0064] Figure 4a illustrates steps in a method 40 for determining the position of a flow diverter implant after expansion within an artery, according to a specific embodiment of the method shown in Figure 2. Identical numerical references between the figures correspond to similar steps or elements. This method can also be implemented by the processing unit 20 shown in Figure 1.

[0065] In step 100, a three-dimensional view Im of an artery to be treated is acquired, for example, by angiography. The three-dimensional image of the artery can be segmented using the "marching cubes" methodology, well-known in the field of image reconstruction. For three-dimensional image construction, see the following publication: Marching Cubes: A high-resolution 3D surface construction algorithm, William E. Lorensen, Harvey E. Cline, Computer Graphics, 1987.

[0066] At step 200, a zone A is identified, manually by an operator or automatically, on the three-dimensional view obtained at the end of step 100. This zone A corresponds to an artery to be treated by the placement of an implant, and may in particular correspond to an aneurysmal pathology of saccular or fusiform type, or any other type of aneurysmal pathology, or a localized narrowing of the artery, or a stenosis, or a thrombosis.

[0067] In an optional step 250, the three-dimensional image Im is verified. The quality of the Im image can be checked by thresholding: the three-dimensional image Im is superimposed on a two-dimensional radiograph viewed from the same angle, to which a threshold is applied. The three-dimensional image can be corrected based on the result of the comparison with the thresholded two-dimensional image, particularly to verify the dimensions of the arterial tree. The three-dimensional image Im can also be rescaled relative to the two-dimensional radiograph.

[0068] It should be noted that steps 100 to 250 are optional for the execution of process 40. Process 40 could be executed by a processing unit receiving as input a three-dimensional image of the artery to be treated with an A zone.

[0069] At step 300, a central line C, or "centreline," of the artery is determined by the treatment means. The central line thus obtained crosses the area to be treated. Advantageously, the central line can be determined according to the methods described previously in relation to process 10 of Figure 2.

[0070] In an optional step (not shown in Figure 2), using the three-dimensional image of the artery and the centerline determined in step 300, the processing unit can, if necessary, correct for a non-existent junction on the actual artery being treated, such as an artery-artery fusion or an artery-aneurysmal sac fusion. Such an error can occur during reconstruction and can also be corrected by the operator.

[0071] At step 400, a flow diverter M corresponding to a preselected reference flow diverter with resting dimensions is positioned at an initial point D, similarly to step 400 of process 10. The flow diverter M is advantageously tubular in shape with a constant radius cross-section, positioned along the centerline C determined in step 300 and centered on said centerline. According to this initial positioning, the flow diverter M may extend beyond the artery walls in certain areas.

[0072] At step 410, the DMI M is discretized into a plurality of segments M j , where the index j indexes the consecutive segments of the DMI M. Very advantageously, each of the segments M j The discretized model is approximated by the processing methods using a cylindrical volume. If the DMI M obtained at the end of step 400 is tubular with a constant radius cross-section, all segments M jThese correspond to tubes of the same radius centered on the central line C. The number of segments can be predetermined and independent of the artery's morphological characteristics, and can, for example, be set to 200. The length of all segments can be the same and taken to be equal to the length of the central line divided by the number of segments. Alternatively, the length of each segment may not be chosen uniformly. For example, the segment lengths can be chosen to obtain a finer mesh in areas where the perimeter of the artery walls is highly variable, or in areas where the central line is significantly deviated. The discretization of the MID can be performed from the initial point D, and therefore from one end of the initial position of the MID to the other end.

[0073] The segmented discretized model obtained at the end of step 410 is used to simulate the final position of the M-shaped implant. This simulation takes into account geometric, mechanical, or both geometric and mechanical constraints exerted by the artery walls on the M-shaped implant. One goal of considering these constraints is to obtain a simulated final position corresponding to the implant's position after its expansion within the artery. Considering the simulation time for a mechanical correction in the general case, initially considering only the geometric constraints exerted by the walls (without seeking mechanical equilibrium at the level of the M-shaped implant walls) saves computation time. We will now detail, with reference to Figure 4b, the final position simulation step according to an embodiment 500, in a first case where geometric constraints are taken into account.

[0074] At step 500, each segment M jThe length and diameter are corrected, taking into account the variation in the intra-arterial radius. As mentioned above, each segment can be approximated by a tubular volume. For each of these segments, a constitutive law of the DMI (Diagnostic Material Interchange) is applied, mechanically relating the length and the diameter. This law is relative, for example, to the previously selected implant reference. This constitutive law can be linear, affine, or nonlinear, and can be determined experimentally, derived from prior analytical development, or provided in a database, for example, if it is supplied by an implant manufacturer. The slope obtained for an affine approximation of the length as a function of the diameter can be negative if the implant, stretched longitudinally, contracts radially, and if compressed longitudinally, it expands radially.The 500 position correction step of the DMI M of the "flow diverter" can be implemented by iterations as follows.

[0075] Steps 501 and 502 are iterated one after the other for each of the segments M j in order.

[0076] In substep 501, the diameter of segment M j is modified, starting from a current position of segment M j stored in a memory of a database accessible from the processing unit. The modification of the diameter Dj of segment M j is made in such a way as to accommodate segment M j in the minimum diameter zone of the portion of artery surrounding segment M j , so that the walls of segment M j touch said minimum diameter zone. It is possible to take into account a maximum diameter of segment M jgiven by a constitutive law; if the minimum diameter of the artery segment is greater than the maximum diameter, then the diameter Dj is modified so as to be equal to the maximum diameter. Then, in substep 502, the length L j of the M segment j is corrected, using the behavioral law of the DMI and the value of the diameter corrected in step 501 for segment M j For example, if the segment M j is retracted radially during step 501, it is elongated in step 502.

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

[0078] In substep 503, the total length L of the DMI M is determined by summing the corrected lengths L j M segments j.

[0079] Following the determination of the geometric position, it may be necessary to correct the position of the DMI if the mechanical equilibrium is not sufficiently satisfactory, starting from the last known position of the DMI, either the position resulting from step 400 or the position resulting from step 500. The processing unit can implement a final position simulation of the DMI M according to a second variant, where mechanical equilibrium is sought for the simulated walls of the DMI M. This second modality corresponds to embodiment 800 for the final position simulation step of the DMI M.

[0080] Sub-steps of this embodiment are detailed in Figure 4c.

[0081] In substep 801, a mechanical model of the DMI is proposed, based for example on the finite element method which takes into account the mechanical links between the different segments of the DMI, in its configuration free of mechanical constraints.

[0082] In substep 802, the segments M are transformed from the constraint-free state read in a database BD2. j in the last known position. For each segment M j , a geometric transformation is applied between the configuration free of mechanical constraints (rest position of the DMI) and the starting configuration of the mechanical correction: - either from step 400 of positioning the DMI according to the initial position, - or from a step 500 of geometric simulation of the final position of the DMI.

[0083] In substep 803, for each segment M jA mechanical model of the contact with the surface of artery 1 is defined by the processing unit. Finally, in substep 804, a non-linear calculation of the mechanical equilibrium for the walls of the MID is performed, with a correction to the position of the Mj segments of the MID being applied if necessary. The final simulated position reached corresponds to a position where the walls of the MID are in the mechanical equilibrium thus calculated.

[0084] Figure 5a schematically illustrates, using the example of artery 1, the change in diameter and length of segments M j , with an index j ranging from 1 to n = 6, during a first iteration of steps 501 to 503. In this figure, the positions of the segments M j The corrected positions are shown in solid lines, and the corrected positions M' jare shown in dotted lines. We observe that the segments of length and diameter corrected to take into account the morphological characteristics of the artery are no longer necessarily connected to each other.

[0085] Next, the length obtained in step 503 for the DMI is compared in substep 504 to the length obtained in the previous iteration of steps 501 to 503. If the resulting total length difference L is sufficiently close to zero (convergence criterion: absolute value of the difference between these lengths), then the iteration loop is terminated, and the lengths L j Segments are determined as the lengths of the implant segments whose final position has been simulated. For example, the absolute value of the difference is compared to a predetermined threshold.

[0086] If, on the other hand, the total length L is not determined to be sufficiently close to the previous total length, then a new iteration of steps 501 to 503 is implemented. To prepare for this new iteration, taking into account the changes made to the lengths and diameters of the segments, the position of the segments is adjusted so that they are connected again, for example, from the initial point D. This is shown in Figure 5b, which corresponds to the same example as that in Figure 5a for the next iteration of steps 501 to 503. The solid line represents the position of the segments before the implementation of substeps 501 and 502 for this iteration: it can be seen that the lengths and diameters of the segments correspond well to the corrected positions in Figure 5a, and that the segments M jwere repositioned one after the other. Repositioning the segments one after the other can again create mismatches between the diameter of the segments and the surrounding walls of artery 1, and lead to a new resizing of the segments.

[0087] Figures 5c and 5d represent the two iterations following those of Figures 5a and 5b, for the same segments. At the end of the iteration shown in Figure 5d, the final length L of the implant is determined to correspond to the sum of the segment lengths.

[0088] At the end of the loop in step 500, the segments are repositioned one after the other, and the simulated position of the implant M after expansion is obtained. The final length of the implant once deployed is therefore taken to be equal to the sum of the lengths L j segments in this simulated position.

[0089] The discretization method described above in relation to steps 400 to 500 is applicable to all types of arterial pathology. It allows for a prediction of the final implant length after expansion that is very close to reality, thus guiding the clinician's choice. The discretization proposed here is advantageous because the corrected lengths of each segment of the model at a given iteration are taken into account for the following iteration.

[0090] According to one embodiment of method 40, the position correction of the M-shaped implant in step 500 takes into account not only the morphological characteristics of the artery, such as the artery's circumference near a segment, but also the degree of longitudinal compression (push / pull) applied by the practitioner during implant placement. Indeed, if a certain force is exerted on the implant during placement, for example, in the direction of longitudinal compression generating radial extension, the implant may locally adopt a circumference that exceeds the circumference of the circle inscribed in the artery walls. The implant may adopt a locally non-tubular shape (with non-circular radial sections).In particular, a longitudinal force can be deliberately applied during the placement of the implant, to radially extend the implant and force its apposition against the walls of the artery, for example in an area where said walls do not have a circular cross-section.

[0091] For example, in the case of a flow diverter segment, the corrected diameter of a segment can be determined based on the surrounding perimeter of the artery walls, which can tend to compress the segment radially, but also by taking into account the longitudinal compression exerted during placement, which can tend to extend the segment radially. To account for the degree of longitudinal compression, the calculation of the corrected diameter of a segment M j step 501 can be achieved by assigning a weight for the influence of the surrounding perimeter of the artery.

[0092] It will be easily understood that the other modalities described above for the implementation of step 500 remain applicable in this case.

[0093] The impact of the longitudinal compression ratio on the simulation of the implant's position after expansion is illustrated in the schematic views of Figure 6. A flow diverter M with an unstressed cylindrical shape is shown on a non-circular section of the walls of artery 1. The top view of Figure 6 shows that the selected M has a resting radius that is too small to be properly apposed against the walls of artery 1.

[0094] For the same implant visible in the middle view of Figure 6, corresponding to an absence of longitudinal compression, the M-shaped implant model is extended radially, such that its diameter approximately reaches the minimum diameter of the walls of artery 1 in the section shown. However, since the artery is not locally circular, there remain areas of the artery where the walls of the implant model are not properly aligned with the walls of artery 1.

[0095] Finally, for the same implant visible in the lower view of Figure 6, with significant longitudinal compression, the radial expansion of the walls of the M-shaped implant is sufficient to achieve complete apposition of the implant against the artery walls, assuming here a perfectly rigid artery. Furthermore, the longitudinal compression is sufficient to impose a locally non-circular shape on the implant after expansion. In reality, the artery surface is not rigid, and the radial force applied by the implant walls in the case of non-zero longitudinal compression can generate deformations of both the implant walls and the artery surface.

[0096] Applying a "push / pull" technique during implant placement allows, for a flow diverter-type implant, for good apposition of the implant against the arterial walls, particularly in areas where the artery is locally non-circular. The variant of step 500 described above takes into account the possibility of applying a "push / pull" technique, thus improving the reliability of the implant simulation.

[0097] Optionally and advantageously, after determining the corrected position of the implant's MID corresponding to the simulated implant position, an additional step 600 is implemented to determine the degree of implant apposition, as shown in Figure 4a. Once the implant's MID position after expansion has been simulated, the processing unit can calculate the degree of apposition as the proportion of the implant surface where the implant walls exhibit good apposition to the arterial walls. For example, in the cases previously shown in Figure 6, 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 easily understood that, in the case of an aneurysmal sac type pathology, and for a "flow diverter" type implant, it is not desirable to obtain good apposition of the walls of the implant against the walls of the aneurysmal sac; on the other hand, it is desirable to obtain good apposition of the device against the other areas of the artery.

[0098] In the case of a DMI that is not a "flow diverter", such as an intra-aneurysmal cage, apposition could be determined by considering the mechanical contact force imposed by the artery wall on the implant walls, or by considering the distances between nodes of the DMI walls and the adjacent artery walls (the DMI being considered correctly apposed below a certain distance threshold).

[0099] Optionally, process 40 may include an additional step 700 for determining the porosity of the walls of the DMI M. This step could alternatively be carried out before step 600 for determining the degree of apposition of the walls of the DMI. The determination of the porosity of the walls of the DMI M is performed according to any method known in the prior art.

[0100] Following the determination of the degree of apposition for the M-shaped implantable device (IMD), independently of the implementation of a step 700 for determining the porosity of the IMD walls, the processing unit can display, via the display device 21, a three-dimensional view of the treated artery with the simulated three-dimensional position of the implant, and further display a map of the degree of apposition over the entire surface of the implant. Such a view is schematically represented in Figure 7, where an artery 1 treated with a flow diverter is visible at zone A along a central line C. For zones 30 and 32, the apposition of the implant against the walls of artery 1 is greater than at the neck of the aneurysm, in zone 31.

[0101] Following an iteration of the DMI deployment positioning method 40, if the determined final position is insufficiently close to the artery walls (for example, if the final apposition is deemed inadequate), a new DMI model can be designed to better approximate the artery walls. A maximum diameter of the M segments can be taken into account. j given by a behavioral law; if the minimum diameter of the artery portion is greater than said maximum diameter, the diameter D j is then modified so as to be equal to said maximum diameter.

[0102] Alternatively, steps 400 and 500 as described above can be repeated with a different implant reference, for example, one with a different nominal diameter. Comparing several final DMI positions obtained for different implant references, possibly varying the positioning of the distal point D and / or the proximal point P, allows the clinician to select the implant reference and interventional modalities best suited to treating the arterial pathology.

[0103] Figure 8a illustrates the result of the DMI positioning step in its initial position for an intra-aneurysmal cage-type DMI. Following step 400, such an implant was positioned in the three-dimensional image of artery 1, according to an initial position Mo, along the central line 2 calculated, for example, according to step 300 described previously. Figure 8b shows the result visible on the graphical interface after an iteration of step 500, which simulates the final position of the DMI, taking into account only the geometric constraints exerted by the intrasaccular walls. This yields a position Mi of the DMI.

[0104] Finally, Figure 8c shows the result visible on the graphical interface, after an iteration of step 800 of the final position simulation of the DMI taking into account the mechanical constraints exerted by the walls, seeking to solve the mechanical equilibrium for the walls of the DMI according to the previously determined position Mi.

[0105] For this example, much more computation time would have been required to calculate the mechanical equilibrium according to step 800 from the initial position Mo, compared to the computation time required here to calculate the position M2 from the position M1 for which geometric constraints exerted by the intra-saccular walls have already been taken into account.

Claims

DEMANDS 1. A method for determining the positioning in the deployed position of an expandable implantable medical device, or IMD, said medical device being intended to be deployed in a vascular structure (1), the method comprising, from a three-dimensional image of a region of interest comprising the vascular structure in which a positioning point (D) of the IMD has been defined, the following steps: - determination (300) of a central line (C) of the artery, - positioning (400) of the DMI (M) according to an initial position, around the central line (C), - simulation (500, 800) of the final position (M) of the DMI after deployment, as a function of constraints exerted by the walls of the vascular structure (1) on the DMI, the method being characterized in that the determination (300) of the central line (C) consists of placing points at different longitudinal positions along the vascular structure, so as to minimize a fluid travel time along said points (Ci) between an entry point (I) in the vascular structure and an exit point (S) of the vascular structure, the travel time being minimized using a gradient descent algorithm, said points forming the central line (C), and in that the simulation of the final position of the DMI is carried out as a function of a longitudinal compression rate intended to be applied to the DMI during its implantation.

2. A method according to claim 1, wherein the determination (300) of the centerline (C) comprises substeps consisting of: - draw (302) the central line (C) passing through said points (Ci); - discretize (303) the vascular structure so as to obtain a succession of three-dimensional portions of the vascular structure along the central line.

3. A method according to claim 1 or 2, wherein the step of positioning the DMI according to the initial position is followed by a step of discretizing the DMI into a set of longitudinal three-dimensional segments, the simulation step of the final position (500) taking into account geometric constraints exerted by the walls of the vascular structure on the DMI, by the following sub-steps: a) for each segment (M j ), modification (501) of the diameter of said segment as a function of the perimeter of the vascular structure in the vicinity of said segment, and modification (502) of the length of said segment, using a behavioral law of the DMI relating said length to said diameter of the segment, b) calculation (503) of a length of the DMI as being the sum of the lengths of the segments at the end of step a), c) comparison (504) of the last two lengths calculated in step b), - if the absolute value of the difference between the last two calculated DMI lengths is less than a threshold, the DMI length in the final position being the last length calculated in step b) and - if said absolute value of the difference is greater than said threshold, the correction step includes a step of adjusting the position of each segment of the DMI taking into account the changes in length of the segments at the end of step a), and a repetition of steps a) to c) with the segments thus modified.

4. A method according to any one of claims 1 to 3, comprising a step of determining a degree of apposition of the DMI on the walls of the vascular structure, in final position.

5. A method according to any one of claims 1 to 4, wherein the final position simulation step (800) takes into account mechanical stresses exerted by the walls of the vascular structure on the DMI, by the following substeps: - assignment (801) of a mechanical model to each segment (Mj), - for each segment (M j ), transformation (802) of the diameter (D j ) of said segment, and assignment of a mechanical contact between said segment (M j ) and the vascular structure (1 ), - resolution (803) of the mechanical equilibrium of the DMI to obtain a final position of the DMI.

6. A method according to any one of claims 1 to 5, comprising a preliminary step (250) of verifying the 3D reconstruction of the surface of the vascular structure in the region of interest, said verification being carried out by thresholding.

7. A method according to any one of claims 1 to 6, comprising after the determination step (300) of the centerline a correction step of one or more non-physiological abutments of said surface, such as an artery-artery fusion or an artery-aneurysmal sac fusion.

8. A method according to claim 3, wherein, if the final position determined for the DMI is insufficiently close to the walls of the vascular structure, the final position simulation step (500) is repeated with segments (M j ) of larger diameters so as to bring the segments closer to the walls of the vascular structure.

9. A method according to claim 6, comprising an additional step of three-dimensional graphical representation of the vascular structure in the region of interest, including the determined central line (C), as well as the degree of apposition.

10. A method according to claim 3, wherein the behavioral law characterizing the contraction of a segment of the DM! is a relationship based on the geometric and mechanical parameters of the DMI. 1 1. Method according to any one of claims 1 to 10 wherein the DMI is of the "flow diverter" type, or intra-aneurysmal cage, or "laser-cut stent".

12. Method according to any one of claims 1 to 1 1, comprising a step (700) of determining a porosity of the walls of the DMI in final position.

13. Product computer program comprising code instructions for carrying out the process according to any one of claims 1 to 12, when executed by processing means of a processing unit.

14. Processing unit (20) configured to obtain a three-dimensional image of vascular structure acquired from an acquisition unit (22), and further configured to simulate a final position of an expandable DMI, by implementing the method according to any one of claims 1 to 12.

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