Method for determining the correct position of windows in relation to the visceral and renal vessels in aortic endoprostheses

Abstract

Method for determining the position of windows in aortic endoprostheses, using images from preoperative CT computed tomography, wherein such endoprosthesis comprises a tubular sleeve (1) having a diameter slightly greater than the diameter of such aorta, on which one or more windows (2) must be made in correspondence with the centre of origin of a blood vessel branching from such aorta. The method comprises the following steps: a) on the axial image of such tomography, calculating the aortic arc of circle (AA) between the position (PB) of such centre of origin of the vessel with respect to a reference point (OA) taken on the circumference of the aorta, b) calculating a conversion parameter (P) dependent on the difference between the diameter of the aortic artery and that of the tubular sleeve (1), c) determining the position of the window (PF) on the prosthesis by calculating the arc of circle on the prosthesis (AM) between a reference point (OM) taken on the tubular sleeve (1), placed in juxtaposition to such reference point (OA) on the aorta (A), and such position (PF), by subtracting the value of such conversion parameter (P) from the value of the aortic arc of circle (AA).

Description

[0001] METHOD FOR DETERMINING THE CORRECT POSITION OF WINDOWS IN RELATION TO THE VISCERAL AND RENAL VESSELS IN AORTIC ENDOPROSTHESES

[0002] The present invention relates to a method for determining the position of windows in aortic endoprostheses. Such prostheses are commonly referred to as fenestrated endoprostheses and are substantially tubular sleeves with cylindrical geometry, usually consisting of a rigid-elastic supportive component referred to as stent, and a covering component referred to as fabric. The materials used for the creation of stents are generally nitmol and steel; these materials have the feature of being compressible and then spontaneously expanding until reaching the nominal diameter. The covering, on the other hand, can be made of biocompatible material such as Dacron or polytetrafluoroethylene (PTFE).

[0003] These are used in surgical procedures in which, in the aortic area affected by an aneurysm, such a tubular prosthesis is released which, by anchoring upstream and downstream on healthy portions of the aorta, serves to "exclude" the dilated part (aneurysm).

[0004] The prosthesis is compressed and loaded onto a semi-rigid sheath that allows it to be inserted through the vessels (in an endoluminal manner) and enables its navigation therein. Subsequently, the endoprosthesis is released in the treatment site, where within a few seconds it is unsheathed by a pull-back mechanism and covers the damaged section of the aorta.

[0005] The tubular endoprosthesis sleeve is normally implanted selecting a diameter slightly greater than the diameter of the artery to be restored, to allow the prosthesis to anchor to its fixation site, also due to its intrinsic radial force, and to promote optimal anchoring and maintenance in position once released.

[0006] When main branch vessels (arteries supplying blood to the intestine or kidneys) originate from the fixation site or aneurysm, fenestrated endoprostheses are characterized by the presence of holes along the walls of the tubular structure of the endoprosthesis, through which another stent can be inserted, connecting the main prosthesis to the target vessel to be maintained perfused with blood. Such holes or windows must be made in exact correspondence with the ostium of origin of the vessel (artery) from the aorta, so that when the prosthesis is positioned, such window is in perfect juxtaposition and there is no risk of vertical or lateral misalignment between the two.

[0007] It is known that this type of prosthesis, particularly when used in the renal and visceral arteries, requires the windows to be made precisely and to vary in position and dimensions from patient to patient. Therefore, the endovascular procedure is feasible only with custom-made prostheses.

[0008] Normally, these custom-made prostheses require long time (approximately three months) to be made and implanted on a patient and also have significant costs.

[0009] The position of the windows is obtained by manufacturing companies through specific measurements and complex mathematical calculations for each individual patient. This is due to the fact that, since the prosthesis has a diameter greater or smaller than the aorta, once the position of the vessel origin from the aorta is measured on the tomographic image, a calculation is to be performed to determine the correct position (coordinates) of the fenestration to be performed on the tubular prosthesis, in terms of vertical and lateral distance, and then adjusted for the various adaptations to the diameter between the aorta and the endoprosthesis.

[0010] In emergency situations, a tubular endoprosthesis without windows must be manually modified by the surgeon, who creates windows manually just before the surgery. This is a complex process that requires accurate measurements and calculations by the surgeon himself / herself, based on the preoperative computerized tomography (CT), exposing the procedure to potential errors.

[0011] Examples of such known methods for calculating the fenestrations are described, for example, in patent application WO / 2022 / 109482.

[0012] The technical problem associated with the present invention is how to simplify and accelerate the calculation of the position of the fenestrations to be performed in an endoprosthesis, for example in real time during a surgical procedure, and thus patientspecific, particularly for use in the renal and visceral arteries.

[0013] The present invention proposes a solution to such problem that involves the use of an algorithm for measuring the positions of the windows on the endoprosthesis, which is fast, accurate, and does not require complex mathematical calculations. This enables the surgeon to obtain the positions of the windows to be made even in emergency settings, when the time available before surgery is very limited (approximately 2 hours). An aspect of the present invention relates to a method for measuring the position of windows in aortic endoprostheses having the features of the enclosed claim 1.

[0014] Further features of the invention are comprised in the dependent claims.

[0015] The features and advantages of the method according to the present invention will become more apparent from the following exemplary and non-limiting description, referring to the attached schematic drawings in which:

[0016] • Figure 1 illustrates an example of a fenestrated endoprosthesis in accordance with the present invention.

[0017] • Figure 2 illustrates an image from CT angiography of the aortic section taken in correspondence with the vessel (a renal artery in the example) where the fenestration must be made in the endoprosthesis.

[0018] • Figures 3a c illustrates the steps of the first processing block for calculating the radial position of the vessel of Figure 2, where the fenestration must be made in the endoprosthesis.

[0019] • Figures 4a and 4b illustrate the steps of the second processing block for calculating the dimension of the vessel of Figure 2, where the fenestration must be made in the endoprosthesis.

[0020] • Figure 5 illustrates a schematic view of a fenestrated endoprosthesis with the measurements carried out according to the method of the present invention highlighted. The method for determining the position of windows in aortic endoprostheses according to the present invention is used to make fenestrations on aortic endoprostheses in the correct position as obtained from the processing of such method. Figure 1 illustrates an aortic fenestrated endoprosthesis manually prepared by the surgeon, configured as a tubular sleeve 1 made of endoprosthesis Dacron + Nitinol. For the purposes of the present invention, it is required that the diameter of the prosthesis in the site where the fenestrations are located be greater than that of the aorta at the corresponding para-visceral aortic segment where the vessels originate; “greater” means a diameter of the endoprosthesis greater by 1% to 45%, preferably 20%, with a diameter of the aorta not exceeding approximately 46 mm. Still for the purposes of the present invention, all distances are conventionally measured in millimetres.

[0021] The fenestrated endoprostheses 1 are characterized by the presence of holes or windows 2 along the walls of the tubular sleeve of the prosthesis, in correspondence with the ostium of origin of a vessel, through which blood can also flow into the arteries originating in the treated section of the aorta via bridging stents.

[0022] The method uses images from preoperative CT computed tomography, from which suitable measurements are obtained for the position of the windows; such measurements can be performed by any operator (manufacturer or surgeon) quickly and with high accuracy. The position in the vertical axis is to be measured as usual. The position on the lateral axis is to be measured by the method as follows.

[0023] On an axial CT image, the position of the vessel origin centre PB is established, preferably by fixing the centre of the vessel V with respect to the aorta A, as illustrated in the sequence of Figures 3a to 3b; a first calculating step is the measurement, in millimetres, of the arc of circle AA between the position of the vessel origin centre PB and the front reference point at 0 degrees OA taken on the circumference C of the aorta, by analysing the images from the preoperative computed tomography.

[0024] The figures illustrate a CT image representing a horizontal section of the aorta, where the upper part is the front zone of the body and the lower part is the rear zone. The reference is preferably taken on the circumference of the aorta in the front zone (vertically in the figure).

[0025] Subsequently, a conversion parameter P is to be applied to the measurement of arc AA, which is calculated as follows, still using the tomographic image, as illustrated in Figures 4a to 4c. The circle corresponding to the diameter of the aorta is divided into four sectors (S) of 90° each. Each sector is further subdivided into a plurality of segments (SS), preferably five segments per sector.

[0026] Each segment is assigned to a value of such conversion parameter, determined by an increasing integer starting from the segment closest to the reference OA (with five segments, the parameters are 1, 2, 3, 4, and 5).

[0027] The correct value of the parameter P to be applied for determining the position of the window to be made will thus be given by the formula:

[0028] “AA - (P = the number of segments where PB falls)”.

[0029] The result of this calculation represents the curved distance AM in mm, to be applied to the endoprosthesis sleeve, as indicated in Figure 5.

[0030] The position of the window to be made on the sleeve is determined by calculating the arc of circle AM measured between the position PF of the window to be made on the prosthesis and the reference point OM taken on the sleeve, placed in juxtaposition to such reference point OA on the aorta.

[0031] AM=AA-P.

[0032] Once such arc of circle is calculated and the reference point OM is known, the fenestration can be performed on the tubular sleeve using the usual instruments supplied to the surgeon.

[0033] By way of example, as illustrated in Figures 3a-3c and 4a-4c, if the value of the arc AA is 15 millimetres and the point PB falls into the third segment, the value of the parameter P to be subtracted from the value of arc AA is 3. Therefore, the value of arc AM is 12 mm (AM=AA-P=15-3=12 mm). This arc value can be easily used during the surgical step by the surgeon to make the window, starting from the clearly visible reference point OM on the sleeve, sliding horizontally along the substantially cylindrical surface thereof.

[0034] This allows a valid 3D fenestration template to be quickly obtained, directly from the preoperative CT computed tomography, without the need for intermediate procedures. The present invention can also be proposed as a program for computer, incorporated as a “plugin” within a program for reading tomographic images in a computerized tomography (CT) machine, which integrates the algorithm so as to automatically return an output containing the coordinates of the fenestrations, without the need to perform any measurements.

[0035] The main advantages of the present invention are:

[0036] - simplicity and speed of execution, as it does not require the use of complex mathematical formulas or dedicated software (from the preoperative CT directly to the valid 3D fenestration template);

[0037] - actuable regardless of the experience and / or background of the operator (engineer, surgeon, or product specialist);

[0038] - possibility of incorporating the algorithm within a DICOM image viewing software.

Claims

CLAIMS1. Method for determining the position of windows in aortic endoprostheses using images from preoperative CT computed tomography, wherein such endoprosthesis comprises a tubular sleeve (1) having a diameter slightly greater than the diameter of such aorta, on which one or more windows (2) must be made in correspondence with the centre of origin of a blood vessel branching from such aorta, said method having the following phases:a) on the axial image of such tomography calculate the aortic arc of circle (AA) between the position (PB) of such centre of origin of the vessel with respect to a reference point (OA) taken on the circumference of the aorta,b) calculate a conversion parameter (P) dependent on the difference existing between the diameter of the aortic artery and that of the tubular sleeve (1), c) determine the position of the window (PF) on the prosthesis by calculating the arc of circle on the prosthesis (AM) between a reference point (OM) taken on the tubular sleeve (1) placed in juxtaposition to such reference point (OA) on the aorta (A) and such position (PF) by subtracting the value of such conversion parameter (P) from the value of the aortic arc of circle (AA).

2. Method according to claim 1, wherein such step of determining a conversion parameter (P) comprises the following steps:• on the axial image of such tomography, subdividing the circle corresponding to the diameter of the aorta (A) into four sectors (S) of 90° each,• further subdividing each sector (S) into a plurality of segments (SS),• assigning to each segment an increasing integer starting from the segment closest to the reference OA,• associating to such conversion parameter the integer corresponding to the segment in which the position of the vessel origin centre (PB) falls.

3. Method according to claim 2, wherein the number of segments (SS) per sector (S) is five and the whole number starts from 1 and increases up to 5.

4. Method according to claim 1, wherein after step c) the fenestration is performed on the tubular sleeve with the usual instruments supplied to the surgeon.

5. Program for computer for determining the position of windows in aortic endoprostheses that implements the steps of the method according to claim 1.

6. Program according to claim 1, characterized in that it is incorporated as a "plugin" within a program for reading tomographic images in a computerized tomography (CT) machine.

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