Method for determining a parameter which is indicative for the position and apposition of a tubular member, such as a stent graft, inserted in a lumen of an anatomical vessel or duct of a patient

Abstract

A method for determining an apposition parameter indicative for the position and apposition of a tubular member, such as a stent graft, inserted in a lumen of an anatomical vessel/duct of a patient. The method includes providing a numerical three-dimensional patient model of at least a part of the vessel including the tubular member; determining a vessel morphology parameter from the patient model, the parameter indicative for the anatomy of a predetermined part of the vessel at or near the tubular member in said vessel with respect to said patient model; determining a tubular member positional parameter from the patient model, the parameter indicative for the position of a predetermined part of the tubular member in the patient model; and calculating, based on the determined vessel morphology parameter and tubular member positional parameter, the relative position of the tubular member with respect to the vessel as the apposition parameter.

Claims

1. A method for determining an apposition parameter which is indicative for the position and apposition of a tubular member inserted in a lumen of an anatomical vessel or duct of a patient, the method comprising the steps of: providing a numerical three-dimensional patient model of at least a part of the vessel of the patient including the tubular member, wherein the three-dimensional patient model comprises three-dimensional positional data of the morphology of the vessel and positional data of the tubular member in said vessel; determining at least one vessel morphology parameter from the patient model, which parameter is indicative for the anatomy of a predetermined part of the vessel at or near the tubular member in said vessel with respect to said patient model; determining at least one tubular member positional parameter from the patient model, which parameter is indicative for the position of a predetermined part of the tubular member in the patient model; and calculating, on the basis of the determined vessel morphology parameter and tubular member positional parameter, the relative position of the tubular member with respect to the vessel as the apposition parameter, wherein: the steps of: determining the vessel morphology parameter comprises determining at least one of the proximal and distal boundary in said vessel suitable for receiving the tubular member; determining the tubular member positional parameter comprises determining the position of the proximal, respectively distal end of the tubular member in said vessel, and; calculating the apposition parameter comprises calculating a ratio between the at least one of the proximal and distal boundary in said vessel and the position of the proximal, respectively distal end of the tubular member; or the steps of: determining the vessel morphology parameter comprises determining a center lumen line extending to the cross sectional centers of the lumen along a predetermined length of the vessel; determining the tubular member positional parameter comprises determining at least one of a proximal and distal end of the tubular member in said vessel and determining the centerline normal to said end surface; and calculating the apposition parameter comprises calculating the angle between the center lumen line and the centerline normal to said end surface; or the steps of: determining the vessel morphology parameter comprises determining an inner surface of the lumen of said vessel suitable for receiving the tubular member; determining the tubular member positional parameter comprises determining the surface of the tubular member in contact with said inner surface of said lumen; and calculating the apposition parameter comprises calculating a ratio between the inner surface of the lumen and the surface of the tubular member in contact with said inner surface.

2. The method according to claim 1, wherein the step of determining the vessel morphology parameter comprises determining at least one of the diameter, length and surface of the vessel suitable for receiving said tubular member.

3. The method according to claim 1, wherein the vessel morphology parameter and the tubular member positional parameter define the anatomy, respectively position in the same three-dimensional coordinate system of the patient model.

4. The method according to claim 1, wherein the step of determining the proximal and/or distal boundary in said vessel comprises identifying in said patient model branch vessels of said vessel.

5. The method according to claim 1, wherein the step of determining at least one of the proximal and distal boundary in said vessel comprises identifying the boundary of the aneurysm by identifying a predetermined increase in vessel diameter in said patient model.

6. The method according to claim 1, comprising: providing a first numerical three-dimensional patient model obtained from a patient at a first point of time and determining at least one of the parameters from said first patient model; providing a second numerical three-dimensional patient model obtained from said patient at a second point of time different from said first point of time and determining at least one of the parameters from said second patient model; and calculating the apposition parameter on the basis of the parameters determined from the two numerical three-dimensional patient models.

7. The method according to claim 6, further comprising the step of providing a numerical three-dimensional pre-operative patient model of at least a part of the vessel of the patient not including the tubular member obtained prior to insertion of the tubular member and calculating at least one of the parameters from said pre-operative patient model.

8. The method according to claim 1, wherein the step of providing a numerical three-dimensional patient model comprises obtaining a three-dimensional image data from a medical imaging technique, such as Computed Tomography (CT), Computed Tomography Angiography (CTA), Magnetic Resonance Imaging (MRI), Magnetic Resonance Angiography (MRA), and the like, and processing said image data for obtaining said numerical three-dimensional patient model.

9. The method for determining an apposition parameter which is indicative for the position and apposition of a stent graft in the thoracoabdominal aorta and/or at least one iliac artery of a patient after endovascular aneurysm repair according to claim 1.

10. The method according to claim 9, wherein the step of determining the vessel morphology parameter comprises determining at least one of the diameter, length and surface of the aortic neck in said patient model.

11. The method according to claim 10, wherein the length and surface of the aortic neck are determined on the basis of the determined proximal and distal boundaries of the aortic neck, wherein the length is determined along the center lumen line, extending to the cross sectional centres of the lumen along a predetermined length of the vessel.

12. The method according to claim 9, wherein the step of determining the vessel morphology parameter comprises identifying the positions in the patient model of at least one branch artery and determining the proximal boundary in said vessel suitable for receiving the tubular member as the position in the patient model on the basis of the positions of the branch artery.

13. The method according to claim 12, wherein the step of calculating the apposition parameter comprises calculating the shortest Euclidean distances in said patient model between the proximal end of the stent graft and branch arteries.

14. The method according to claim 9, wherein the step of determining the vessel morphology parameter comprises determining the distal boundary of the aortic neck, wherein determining the distal boundary comprises at least one of: in the patient model, determining the first slice perpendicular to the center lumen line of the aortic neck that shows interruption of full circumferential stent graft apposition; and in a pre-operative patient model of at least a part of the vessel of the patient not including the tubular member obtained prior to insertion of the tubular member and calculating at least one of the parameters from said pre-operative patient model, determining the first slice to exceed a 10% increase of the average aortic diameter at baseline.

15. The method according to claim 9, wherein the step of determining the tubular member positional parameter comprises identifying the proximal end of the stent graft in the patient model on the basis of proximal located markers and/or a proximal end of the stent frames on said stent graft.

16. The method according to claim 9, wherein determining the tubular member positional parameter comprises determining a resting or initial diameter of the stent graft and determining from the patient model the diameter of the stent graft, wherein the apposition diameter is determined as a ratio between the two determined diameters.

17. A method for determining an apposition parameter which is indicative for the position and apposition of a stent graft inserted in a lumen of an anatomical vessel or duct of a patient, the method comprising the steps of: providing a numerical three-dimensional patient model of at least a part of the vessel of the patient including the stent graft, wherein the three-dimensional patient model comprises three-dimensional positional data of the morphology of the vessel and positional data of the stent graft in said vessel; determining at least one vessel morphology parameter from the patient model, which parameter is indicative for the anatomy of a predetermined part of the vessel at or near the stent graft in said vessel with respect to said patient model; determining at least one stent graft positional parameter from the patient model, which parameter is indicative for the position of a predetermined part of the stent graft in the patient model; and calculating, on the basis of the determined vessel morphology parameter and stent graft positional parameter, the relative position of the stent graft with respect to the vessel as the apposition parameter.

18. The method according to claim 17, comprising: providing a first numerical three-dimensional patient model obtained from a patient at a first point of time and determining at least one of the parameters from said first patient model; providing a second numerical three-dimensional patient model obtained from said patient at a second point of time different from said first point of time and determining at least one of the parameters from said second patient model; and calculating the apposition parameter on the basis of the parameters determined from the two numerical three-dimensional patient models.

19. The method for determining an apposition parameter which is indicative for the position and apposition of a stent graft in the thoracoabdominal aorta and/or at least one iliac artery of a patient after endovascular aneurysm repair according to claim 17.

20. A method for determining a risk parameter indicating the risk of post-stent graft complication, comprising the steps of: determining, for at least a first numerical three-dimensional patient model obtained from a patient at a first point in time and a second numerical three-dimensional patient model obtained from said patient at a second point of time different from said first point of time, apposition parameters indicative for the position and apposition of a tubular member inserted in a lumen of an anatomical vessel or duct of a patient, wherein the risk parameter is defined as at least one of: an increase or decrease of the surface of the aortic neck in said patient models; an increase of the parameter based on the shortest Euclidean distances in said patient models between a proximal end of the tubular member and a branch artery; an increase of the parameter based on an angle between a center lumen line extending to a cross-sectional center of the lumen along a predetermined length of the vessel and a centerline normal to the surface of at least one of a proximal and a distal end of the tubular member in said vessel; an increase of the parameter based on a resting or initial diameter of the tubular member and the diameter of the tubular member determined from the patient model; a decrease of the parameter based on an inner surface of the lumen of said vessel suitable for receiving the tubular member and the surface of the tubular member in contact with said inner surface of said lumen; and a decrease in the distance between the proximal end of the tubular member and the distal boundary of the neck.

Description

(1) The present invention is further illustrated by the following Figures and examples, which show a preferred embodiment of the device and method according to the invention, and are not intended to limit the scope of the invention in any way, wherein:

(2) FIG. 1 schematically shows the method according to the invention.

(3) FIGS. 2 and 3 show different parameters for determining the position and apposition of an stent graft in an aorta;

(4) FIGS. 4-8 show stent graft position and apposition of different patients; and

(5) FIG. 9 schematically shows an overview of the parameters in relation to the aortic neck.

(6) In FIG. 1, the method 100 according to the invention is schematically shown. The method according to the invention is preferably an automated, for instance computer implemented, method. The method can be performed by a standard computer, a dedicated processing unit or any suitable device.

(7) The method is arranged to derive parameters from imaging data, which can for instance be imaging data obtained by an imaging device IM based on Computed Tomography (CT), Computed Tomography Angiography (CTA), Magnetic Resonance Imaging (MRI), Magnetic Resonance Angiography (MRA), and the like. From this imaging device, the imaging files may be stored and processed for obtaining digital patient models 1a-c which contain three-dimensional positional data of the morphology of the aorta and the stent inserted therein. In this example, dataset 1a contains preoperative data, such that this patient model does not contain information regarding the stent.

(8) A processor PROC processes the patient models 1a-c and determines from the data parameters relating to the vessel morphology, indicated with VESSEL and/or parameters relating to the stent graft position, indicated with TUBE. As said, it may be possible that only vessel related parameters or only tube related parameters are calculated, for instance for comparison of these parameters between patient models 1a-c.

(9) The parameters are processed by a second processor PROC2, which may be same processor as mentioned above, for determining a parameter PAR which is representative for the position and apposition of the stent graft in the aorta. This parameter, or the plurality of parameters, may be stored in a memory 2.

EXAMPLE

(10) Five EVAR patients were retrospectively selected from St. Antonius Hospital's database. Four have been electively treated for an abdominal aortic aneurysm with occurrence of late (>1 year) type IA endoleak or significant endograft migration (>1 cm). A fifth patient without post-EVAR complications during follow-up was used as control. All patients underwent at least a pre-EVAR CT-scan and two post-EVAR CT-scans before the migration or type IA endoleak was determined. All CT-scans were part of regular EVAR follow-up and were assessed by radiologists according to a standardized protocol.

(11) CT Scan Protocol

(12) CT Angiography images were acquired on a 256 slices CT scanner. Scan parameters were: Tube voltage 120 kV, tube current time product 180 mAs preoperative and 200 mAs postoperative, distance between slices 0.75 mm, pitch 0.9 mm, collimation 128×0.625 mm preoperative, and 16 mm×0.75 mm postoperative. Preoperative slice thickness was 1.5, 3.2, 3.2, 2.0, and 3.0 mm for patients #1-#5 respectively. Postoperative slice thickness was 1.5 mm for all postoperative CT scans. Pre-EVAR, 100 ml Xenetix300 contrast was administered intravenously in the arterial phase with 4 ml per second. Post-EVAR, 80 ml was administered in the arterial phase with 3 ml per second.

(13) Measurement Protocol

(14) The aortic neck morphology was defined on the preoperative CT scan and every available post-operative CT scan of each patient. With use of the software implementing the method according to the invention, the position and apposition of the endograft within the aortic neck were determined for each patient at the post-operative CT scans.

(15) Neck Morphology

(16) The aortic neck characteristics included diameter, length and surface. The measurements were performed by an experienced observer on a 3Mensio vascular workstation V7.2 (Pie Medical, Maastricht, The Netherlands). A center lumen line (CLL) was drawn through the lumen of the aorta. The neck diameter was measured at the level of the distal boundary of the orifice of the lowest renal artery. The aortic neck length was measured as the distance over the CLL between the lowest renal artery and the distal end of the neck. On preoperative CT scans, the distal end of the neck was defined as a 10% increase in aortic diameter compared to the diameter at the level of the lowest renal artery. On postoperative CT scans, the distal end of the aortic neck was determined as the level where full circumferential apposition of the endograft with the aortic wall was lost. This is called the distal apposition boundary.

(17) Dedicated software, developed in MATLAB 2015a (The MathWorks, Natick, Mass., USA), calculated the surface over a 3D mesh of the aortic lumen using the coordinates of the renal arteries and the coordinates of the distal end of the aortic neck. The mesh and coordinates were exported from 3Mensio.

(18) The aortic neck surface (ANS) was calculated with this homemade software and defined as the neck surface that can be used for endograft apposition without overstenting one of the renal arteries R. The proximal boundary PB (FIG. 2A and FIG. 9) of the ANS was defined by the orifices of both renal arteries R. Pre-EVAR the ANS ends were the diameter of the neck is >10% of the diameter at the lowest renal artery R (the artery in the left of FIG. 2a), indicated with DN. Post-EVAR (FIG. 2B), the ANS ends when the full circumferential endograft apposition with the aortic wall is lost, also indicated with DN in FIG. 2B. The aortic neck surface was calculated over the aortic segment that was located between these boundaries PB, DN.

(19) Endograft Position

(20) The endograft position was defined by the terms fabric distances, tilt and endograft expansion. These characteristics were calculated with the software on the basis of the proximal end of the endograft fabric (PEF), see FIGS. 3A and 9. The PEF was defined by identification of the 3D coordinates of the endograft fabric markers measured in 3Mensio. With use of the software the PEF can be projected on the mesh of the aortic lumen AL.

(21) The fabric distances are the Euclidean straight-line distances from the PEF to the coordinates of both renal arteries R (FIG. 3A). The shortest fabric distance (SFD) and longest fabric distance (LFD) are independent of which renal artery R is the highest on CLL measurements. Increase in either SFD or LFD during follow-up will be indicative for endograft migration.

(22) Tilt T of the endograft in the aorta was defined as the angle between the centerline CLL of the aortic neck and the centerline CL of the PEF (FIGS. 3B and 9). Endograft expansion is calculated as the average diameter of the PEF of the endograft (3D intersection with the aortic neck) and measured as absolute value as well as percentage of the original maximum possible endograft diameter. Endograft expansion may be the result of neck dilatation, endograft tilt and migration. The relationship between endograft expansion and oversizing is shown in Table 1.

(23) TABLE-US-00001 TABLE 1 Relationship between endograft oversizing and endograft expansion. This relationship is independent of the endograft diameter. Oversizing of endograft [%] 10 15 20 25 Endograft expansion [% of original endograft 91 87 83 80 diameter]

(24) The method allows determination of all parameters at the first post-EVAR CT scan as baseline and eventual changes during follow-up.

(25) Endograft Apposition

(26) The endograft apposition surface (EAS) is defined as the surface of the aortic neck where the endograft seals the aortic wall. This parameter can be calculated as absolute value as well as percentage of the maximum aortic neck surface (ANS) that could be sealed. The EAS was calculated as the surface over the mesh of the aortic lumen between the PEF and the distal apposition boundary (FIG. 1C). A decrease of EAS may be an early indicator of endograft migration or neck dilatation.

(27) Because of the 3D intersection of the endograft with the aortic wall the lowest point of the endograft fabric will not always be straight below the renal arteries. Therefore, we defined the shortest apposition length (SAL) which is the shortest distance between the endograft fabric PEF and the distal apposition boundary DN somewhere at the 3D intersection between endograft and aortic wall (FIGS. 3c and 9).

(28) Warning Signs

(29) Initial suboptimal endograft placement, observed on the first postoperative CT scan, and change in position and apposition during follow-up may forecast the onset of post-EVAR complications. On the basis of the new measuring software six parameters can describe aortic neck morphology and the initial position and apposition of the endograft in the aortic neck, as listed in table 2 below:

(30) TABLE-US-00002 TABLE 2 Baseline parameters at first postoperative CT scan Aortic neck surface (ANS) Fabric distances (SFD, LFD) Tilt of the endograft Endograft expansion (% of the original endograft diameter) Endograft apposition surface (EAS, % of ANS) Shortest apposition length

(31) These parameters at the first postoperative CT scan are used as baseline for follow-up. During follow-up, subtle changes in ANS, endograft position, and EAS may occur before type IA endoleak of substantial migration are obvious. In table 3, 7 warning signs that indicate change in endograft position during follow-up are described.

(32) TABLE-US-00003 TABLE 3 Warning signs that indicate change in endograft position during follow-up, potentially predicting migration and type IA endoleak. Increase of ANS (neck dilatation) Decrease of ANS (loss of apposition at distal apposition zone) Increase of fabric distance (SFD, LFD) Increase of endograft tilt Increase of endograft expansion (% of the original endograft diameter) Decrease of EAS (% of ANS) Decrease of shortest apposition length

(33) These warning signs were analysed on the CT scans of five patients, in order to illustrate the added value over regular (and current standard) follow-up.

Patient Examples

(34) Five EVAR patients were selected, one without late aortic neck associated complications (patient #1), and four diagnosed with endograft migration or type IA endoleak after >1 year follow-up. Two patients suffered from type IA endoleak (patients #2 and #3, diagnosed 493 and 1273 days after the primary procedure, respectively). Two patients were diagnosed with significant (>1 cm) migration (patients #4 and #5, diagnosed 1197 and 1659 days after the primary EVAR procedure, respectively).

(35) Patient #1

(36) FIGS. 4A-C and Table 4 show a case of stable endograft position and EAS without early or late neck associated complications one year post-EVAR.

(37) FIG. 4A shows the pre-EVAR aortic neck surface (ANS) between the renal arteries R and the distal end of the neck DN. FIG. 4B shows that the endograft EAS is well positioned just at the level of the lowest renal artery RL 41 days post-EVAR. According to FIG. 4C there are no warning signs in position and apposition of the endograft compared with the first follow-up CT scan at 393 days post-EVAR (besides slight increase in tilt).

(38) No warning signs were detected at the last follow-up CT scan compared to the first follow-up CT scan (Table 4). Endograft expansion increased slightly, but the endograft was still 19% oversized at one year follow-up.

(39) TABLE-US-00004 TABLE 4 Neck characteristics and endograft position and apposition for patient #1. Pre-EVAR Post-EVAR Post-EVAR 48 days 41 days 393 days Neck diameter (mm) 24 24 25 Original endograft 28 [Endurant.sup.a] diameter (mm) [type] Neck length (mm) 43 SFD (mm)  0  0 LFD (mm) 11 12 Tilt (°)  3  8 Endograft expansion  23 [80%]  24 [84%] [mm, and % original endograft diameter] Shortest apposition 28 28 length (mm) ANS (mm.sup.2, and % of  2704 (100%)  2907 [108%] the first post-EVAR CT scan) EAS (mm.sup.2, and % of 2330 [86%] 2544 [88%] the ANS) .sup.aMedtronic, Minneapolis, Minn., USA SFD = Shortest Fabric Distance LFD = Longest Fabric Distance ANS = Aortic Neck Surface EAS = Endograft Apposition Surface
Patient #2

(40) FIGS. 5A-C and Table 5 show the results of a patient were the endograft position at the first post-EVAR CT scan was insufficient, and four warning signs were observed (FIG. 5B); 1. Fabric distance to the lowest renal artery is 10 mm, 2. shortest apposition length is only 3 mm, 3. endograft expansion is 98% of the original diameter (only 2% oversizing), and 4. the EAS is only 24% of the ANS (see FIG. 5A). The completion angiography during the EVAR procedure showed that the endograft was positioned 1-2 mm below the lowest renal artery, so the endograft must have been migrated between the primary implant and the first post-EVAR CT scan. The radiologist scored the position of the endograft on this first follow-up CT scan as “uneventful” with adequate sealing and no evidence for endoleaks. On the second follow-up CT scan all warning signs remained present and a type IA endoleak and a complete loss of endograft apposition were visible (FIG. 5C).

(41) TABLE-US-00005 TABLE 5 Neck characteristics and endograft position and apposition for patient #2. Pre EVAR Post-EVAR Post-EVAR 21 days 59 days 493 days Neck diameter (mm) 23 25 23 Original endograft 26 [Talent.sup.a] diameter (mm) [type] Neck length (mm) 11 SFD (mm) .sup. 10.sup.b 13.sup.b LFD (mm) 15 17 Tilt (°)  3  2 Endograft expansion [mm,  26 [98%].sup.b  26 [100%].sup.b and % original endograft diameter] Shortest apposition length .sup.  3.sup.b  0.sup.b (mm) ANS (mm.sup.2, and % of the 1465  1298 [89%] first post-EVAR CT scan) EAS (mm.sup.2, and % of the 355 [24%].sup.b  45 [3%].sup.b ANS) .sup.aMedtronic, Minneapolis, Minn., USA .sup.bWarning signs SFD = Shortest Fabric Distance LFD = Longest Fabric Distance ANS = Aortic Neck Surface EAS = Endograft Apposition Surface
Patient #3

(42) FIGS. 6A-F and Table 6 show a patient diagnosed with a type IA endoleak 1273 days post-EVAR. The preoperative neck is of sufficient length, indicated with ANS in FIG. 6A and not angulated. A large endograft apposition surface (EAS) is visible 38 days post-EVAR. On the 251 days post-EVAR CT scan, two important warning signs are present (FIG. 6B): 1. Substantial increase of the ANS as a result of neck dilatation that is not observed at baseline level, 2. Expansion of the endograft diameter (change from 33% initial oversizing to 15% oversizing at 251 days follow-up). FIGS. 6C-E show a progressive dilatation of the aortic neck occurs during 251-911 days follow-up, without migration of the endograft. On the 911 days post-EVAR CT scan (FIG. 6E), the endograft oversizing was reduced to 9%. The radiologist reported no dilatation of the aortic neck, but only an increase of the aneurysm diameter without signs of an endoleak. A type IA endoleak was observed on the CT scan 1273 days post-EVAR (FIG. 6F).

(43) TABLE-US-00006 TABLE VI Aortic neck characteristics and endograft position and apposition for patient #3. Post- Post- Post- Post- Post- EVAR Pre-EVAR EVAR EVAR EVAR EVAR 1273 28 days 61 days 251 days 541 days 911 days days Neck diameter (mm) 21 21 21 21 22 22 Original endograft 28 diameter (mm) [type] [Endurant.sup.a] Neck length (mm) 14 SFD (mm) 6 6 6 6  6 LFD (mm) 9 7 9 7 .sup. 13.sup.b Tilt (°) 17 18 13 16 15 Endograft expansion  21 [75%]   24 [87%].sup.b   24 [87%].sup.b   26 [92%].sup.b  27 [95%].sup.b [mm, and % original endograft diameter] Shortest apposition 22 29 28 28  .sup. 0.sup.b length (mm) ANS (mm.sup.2, and % of 2578  3444 [134%].sup.b  3638 [141%].sup.b  3594 [139%].sup.b 1026 [40%].sup.b the first post-EVAR CT scan) EAS [mm.sup.2, and % of 2051 [80%] 2855 [83%] 3006 [83%] 2955 [82%]  231 [23%].sup.b the ANS) .sup.aMedtronic, Minneapolis, Minn., USA .sup.bWarning signs SFD = Shortest Fabric Distance LFD = Longest Fabric Distance ANS = Aortic Neck Surface EAS = Endograft Apposition Surface
Patient #4

(44) FIGS. 7A-C and table 7 show a patient with increasing tilt of the endograft during follow-up. No warning signs were present on the CT scan 32 days post-EVAR, with the exception of substantial tilt (FIG. 7B). On the second post-EVAR CT scan (FIG. 7C), multiple warning signs were present: 1. An increase in tilt (from 20.0° to 28.5°), which results into 2. Increased endograft expansion of 99% of the initial diameter (only 1% oversizing left), and 3. Decrease in EAS. No endoleak was reported after 1659 days follow-up. Four months later, a type IA endoleak was diagnosed with duplex ultrasound.

(45) TABLE-US-00007 TABLE 7 Aortic neck characteristics and endograft position and apposition for patient #4. Pre-EVAR Post-EVAR Post-EVAR 57 days 32 days 1659 days Neck diameter (mm) 27 27 28 Original endograft 29 [Excluder.sup.a] diameter (mm) [type] Neck length (mm) 33 SFD (mm)  2  4 LFD (mm) 19 24.sup.b Tilt (°) .sup. 20.sup.b 29.sup.b Endograft expansion [mm,  25 [87%]  28 [99%].sup.b and % original endograft diameter] Shortest apposition length 20 15.sup.b (mm) ANS (mm.sup.2, and % of the 2425  2680 [110%] first post-EVAR CT scan) EAS [mm.sup.2, and % of the 1658 [68%] 1492 [56%].sup.b ANS) .sup.aW. L. Gore & Associates, Inc., Flagstaff, Arizona, USA. .sup.bWarning signs SFD = Shortest Fabric Distance LFD = Longest Fabric Distance ANS = Aortic Neck Surface EAS = Endograft Apposition Surface
Patient #5

(46) FIGS. 8A-E and table 8 show a case of endograft migration, tilt, and aortic neck dilatation. FIG. 8a shows the pre-EVAR neck surface ANS. According to FIG. 8B, a good endograft apposition surface EAS is achieved 86 days post-EVAR. On the 369 days follow-up CT scan (FIG. 8C), three warning signs were observed: 1. Increased tilt of the endograft, 2. Migration of 3 mm at the level of the lowest renal artery RL, and 3. Increased expansion of the endograft. After 890 days (FIG. 8D), almost all warning signs were present. The aortic neck was dilated, leading to further expansion of the endograft and decreased sealing at the distal part of the neck. The endograft had been migrated and EAS was obviously decreased. In the radiology only endograft migration was determined at the 890 days post-EVAR CT-scan and no reintervention was performed. On the 1197 days CT scan (FIG. 8E), complete loss of apposition and subsequent type IA endoleak was observed.

(47) The present invention is not limited to the embodiment shown, but extends also to other embodiments falling within the scope of the appended claims.