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EP-4739218-A1 - METHOD AND SYSTEM FOR ASSESSING STRUCTURAL INTEGRITY OF HOLLOW EXPANDABLE STRUCTURES

EP4739218A1EP 4739218 A1EP4739218 A1EP 4739218A1EP-4739218-A1

Abstract

Methods and systems are disclosed for assessing the structural integrity of a hollow expandable structure subject to expansion and contraction. The disclosed methods use a combination of expandable structure wall strain calculation and expandable structure wall tension calculated from 3D images (or 3D images assembled from 2D images) of the expandable structure captured at different states of expansion of the expandable structure. The calculated wall strain and wall tension are independent of wall thickness and wall material properties.

Inventors

  • MILLER, Karol Stanislaw
  • JOLDES, Grand Roman
  • WITTEK, Adam Slawomir
  • BOURANTAS, George

Assignees

  • THE UNIVERSITY OF WESTERN AUSTRALIA

Dates

Publication Date
20260513
Application Date
20240628

Claims (9)

  1. CLAIMS 1. A method of assessing the structural integrity of a hollow expandable structure subject to expansion or contraction, using a combination of expandable structure wall strain calculation and expandable structure wall tension calculation calculated from 3D images of the expandable structure captured at different states of expansion of the expandable structure, wherein the calculated wall strain and wall tension are independent of wall thickness and wall material properties.
  2. 2. The method of claim 1, wherein the method comprises the steps of: obtaining a first set of 3D images of the expandable structure at a first state of expansion; obtaining at least one second set of 3D images of the expandable structure, each second set of images captured at a state of expansion different from the first state of expansion; calculating wall strain(ε) between the first and second expansion states based on relative displacement of a plurality of points on the structure between at least one 3D image from the first set and at least one 3D image from the second set; obtaining data indicative of a load pressure on the expandable structure; generating a 3D discretisation of geometry of the wall of the expandable structure based on any one or more of the 3D images, providing a sample of wall characterising points defining the wall; calculating wall stress based on solid mechanics; calculating wall tension from the calculated wall stress for the plurality of wall surface characterising points by stress field integration over the wall thickness; and calculating a structural integrity index (SII) based on a comparison between the calculated tension and the computed strain for each one of the plurality of wall characterising points.
  3. 3. The method as claimed in claim 2, wherein wall strain is calculated by: registering at least one 3D image from the first set and the at least one 3D image from the second set to obtain a displacement field between the first and second expansion states based on relative displacement between corresponding voxels, computing deformation gradient components of the wall of the expandable structure based on the displacement field; and computing strain (ε) in the wall for at least a plurality of the wall characterising points from the wall deformation gradient.
  4. 4. The method as claimed in claim 2, wherein wall strain is calculated by: registering at least one 3D image from the first set and the at least one 3D image from the second set to obtain a displacement field between the first and second expansion states based on relative displacement between corresponding voxels, computing deformation gradient components of the wall of the expandable structure based on the displacement field; and estimating wall strain (ε) from selected deformation gradient components.
  5. 5. The method as claimed in claim 2, wherein wall strain is calculated by: generating by segmentation a first state 3D model of geometry of the expandable structure based on one of the 3D images of the first set of images; generating by segmentation a second state 3D model of geometry of the wall of the expandable structure based on one of the 3D images of the second set of images; registering the first state 3D model of geometry and the second state 3D model of geometry to determine relative displacement of the plurality expandable structure characterising points between the first state 3D model of geometry in the second state 3D model of geometry; and calculating strain between each of the wall characterising points from relative displacement between the two expansion states of the expandable structure.
  6. 6. The method as claimed in claim 2, wherein wall strain is calculated by: generating a mesh of at least one 3D image or its 3D model of geometry from the first set of images; generating a mesh of at least one 3D image or its 3D model of geometry from the second set of images; registering the mesh of the first state 3D image or model of geometry and the mesh of the second state 3D image or model of geometry to determine relative displacement of the plurality expandable structure characterising points between the first state 3D mesh and the second state 3D mesh; and calculating strain between each of the wall characterising points from relative displacement between the two expansion states of the expandable structure.
  7. 7. The method of any one of claims 2 to 6 wherein the structural integrity index (SII) is a function of the calculated tension and strain.
  8. 8. The method as claimed in any one of claims 2 to 7 further comprising calculating a relative structural integrity index by dividing structural integrity index by its average value.
  9. 9. The method as claimed in any one of claims 2 to 8 wherein the wall stress is calculated using a finite element method 10. The method as claimed in any one of claims 2 to 9 wherein the wall stress is calculated using a meshless method. 11. The method as claimed in any one of claims 2 to 10 wherein the SII is calculated: SII = Maximum Principal Wall tension /(1+ Maximum Principal ε). 12. The method as claimed in any one of claims 2 to 10 wherein the SII is calculated: SII = Maximum Principal Wall tension / (1+Maximum tangential strain). 13. The method as claimed in claim 11 or claim 12 wherein the SII is calculated for every wall characterising point of the expandable structure wall. 14. The method as claimed in any one of claims 8, and 11, 12 or 13 when dependent on claim 8 further comprising the step of visualising the ratio of SII and RSII. 15. The method as claimed in any one of the preceding claims wherein the expandable structure is a flexible expandable structure. 16. The method as claimed in claim 15 wherein the flexible expandable structure is a biological expandable structure. 17. The method as claimed in claim 16 wherein the expandable structure is an aortic aneurysm. 18. The method as claimed in claim 17 wherein the sets of 3D images include a systolic image and a diastolic image. 19. The method as claimed in any one of claims 1 to 18 further comprising, a) calculating further wall strain between any previous state and a further state of the expandable structure based on a further one of the second sets of images; b) calculating a structural integrity index (SII) for each one of the plurality of wall characterising points based on comparison between the calculated tension for the point and the further computed strain for each point. 20. The method as claimed in claim 19 further comprising the step of choosing a further one of the sets of second images and repeating steps a) and b) for the further set of second images. 21. The method as claimed in any one of claims 1 to 20 wherein the wall characterising points are located on an inner wall surface of the expandable structure. 22. The method as claimed in any one of claims 1 to 21 wherein the wall characterising points are located on an outer wall of the expandable structure.

Description

METHOD AND SYSTEM FOR ASSESSING STRUCTURAL INTEGRITY OF HOLLOW EXPANDABLE STRUCTURES Technical field The disclosure relates to automated analysis of captured images to identify structural impairment of a hollow expandable structure, and potentially identify weaknesses in the structure from the image analysis. A particular application of embodiments is for analysis of flexible expandable structures, such as those given by medical images of organs or vessels, such as the aorta, to identify indicators of potential risk, such as aneurysm disease progression and aneurysm rupture risk. Background Aortic aneurysm (AA), or more specifically Abdominal Aortic Aneurysm (AAA) is a chronic asymptomatic disease of the elderly (> 65 years). AAA rupture is a catastrophic event with mortality exceeding 90%. Clinical decisions (essentially whether to operate or to put a patient on surveillance) are currently based on AAA maximum diameter without any consideration for mechanical/biomechanical factors. Most AAAs are asymptomatic, and they are often diagnosed opportunistically during clinical examination or investigation for another condition. The most important complication of AAA, aortic rupture, is a catastrophic clinical event. Most patients will not survive and overall AAA causes ~200,000 deaths per year worldwide. Australia has a high overall prevalence (7.2%) of an AAA defined as 30 mm or larger in diameter in men over 64 (in women it is ~4 times lower). Although the overall mortality has halved in the last decade, Australia has a very high rate of surgical intervention compared to other western countries. In 2019 the European Society for Vascular Surgery and National Institute for Health and Care Excellence (UK) published updated guidelines on AAA management confirming the burden of disease and indications for interventional treatment, which is based on a maximum AAA diameter > 5.5 cm for men and 5 cm for women. Yet, in Australia 40% of all AAA undergo intervention below this threshold despite the fact that data from the National Health System (NHS, UK) screening programme show that, for aneurysms below 5.5 cm, the rupture rate is 0.4% per year, which is lower than the risk from operation, and many AAA cases remain quiescent in a patients’ lifetime. This raises the question on how to best manage AAA’s as there is a balance between intervention to prevent AAA rupture versus overtreatment that may cause harm. The current management of intact AAA’s is based primarily on the maximum aortic diameter. If the diameter is < 5.5 cm for men and 5 cm for women, the patient is usually placed on a program of surveillance, with regular ultrasound examinations or CT scans to monitor growth. If the diameter exceeds 5.5 cm for men and 5 cm for women, or the AAA is expanding rapidly (> 4 mm in 6 months or >10 mm in one year), surgical intervention is typically recommended. Regardless of the type of repair planned, it is the decision and timing of intervention that causes the most concern amongst patients and clinicians. Currently a 'one size fits all' approach is applied to AAA care, and as such is not suitable for all patients. A rupture prediction criterion derived from population statistics does not take into account the particular circumstances of a given patient. It is estimated that as many as ten operations are performed to prevent one AAA rupture and probably at least 75% of AAAs do not actually rupture, yet as many as 0.4% per year smaller aneurysms in patients under surveillance do rupture. Therefore, there is an unmet need for improved patient stratification. Given the many limitations of the current clinical definition of ‘high-risk’ of rupture, based mainly on the maximum diameter of the AAA, many researchers across both engineering and medical disciplines believe that biomechanics-based patient-specific modelling (PSM) could have major clinical potential to provide more accurate patient-specific rupture risk assessment. Summary of the Invention According to one aspect there is provided a method of assessing the structural integrity of an expandable structure subject to expansion or contraction, using a combination of expandable structure wall strain calculation and expandable structure wall tension calculation, calculated from 3D images of the expandable structure captured at different states of expansion of the expandable structure, wherein the calculated wall strain and wall tension are independent of wall thickness and wall material properties. In some embodiments the method comprises the steps of: obtaining a first set of 3D images (possibly of different modalities) of the expandable structure at a first state of expansion; obtaining at least one second set of 3D images (possibly of different modalities) of the expandable structure, each second set of images captured at a state of expansion different from the first state of expansion; calculating wall strain (ε) between the first and second expansion states based o