{"id":{"repo_id":"cadiz","oai_identifier":"oai:rodin.uca.es:10498/39996"},"canonical_url":"https://search.dev.ndltd.org/etd/cadiz/oai:rodin.uca.es:10498/39996","repository":{"repo_id":"cadiz","name":"Universidad de Cadiz","base_url":"https://rodin.uca.es/oai/request"},"display":{"title":"Development and Validation of Non-Invasive Methods for the Identification of Patient-Specific Hyperelastic and Anisotropic Material Properties of Abdominal Aortic Aneurysms In Vivo","abstract":"An abdominal aortic aneurysm (AAA) is a permanent local dilatation of the human abdominal aorta, posing a severe health risk due to a rupture related mortality rate of up to 85 percent. Current clinical risk assessment relies on a population derived threshold value for the maximum aneurysm diameter. However, this global metric ignores local tissue alterations from remodeling processes affecting the biomechanical properties of the vessel wall. These changes create heterogeneous deformations and vulnerable regions prone to rupture. Consequently, the diameter based criterion allows limited individual risk stratification, risking unnecessary surgeries or missed critical cases. Currently, no clinically established patient specific biomarker reliably predicts rupture risk. This work focuses on developing and validating non invasive, in vivo applicable methods to characterize the elastic properties of different AAA tissue regions. Additionally, it pursues material behavior identification using a hyperelastic and anisotropic material model. The goal is to provide patient specific markers alongside the diameter criterion to assess individual rupture risk. The central measurement technique is high resolution 4D ultrasound (3D and time) combined with speckle tracking (4D US), enabling spatially and temporally resolved assessment of local wall deformations. The first study developed a method to improve the reliability of single ultrasound acquisitions, reflecting current clinical standards. A comprehensive analysis approach combined multiple estimates of wall deformation from a single acquisition into an averaged model. Using in vivo data from 10 AAA patients, strains were calculated in wall regions with structurally different properties, such as calcifications. The ability to distinguish these regions using 4D US indicates sufficient resolution to differentiate potentially rupture prone regions from more stable areas. Using the averaged models, all patients could be significantly distinguished based on circumferential strain compared to only 25 percent using individual measurements. This enables reliable individual level statements for the first time. The second study extended the focus to thrombotic regions using data from an animal study involving ten apolipoprotein E deficient mice. By comparing in vivo findings with histological cross sections, a new method assigned measured wall strains to five different tissue regions within the vessel wall and thrombus areas. The analysis demonstrated that 4D US can reliably differentiate between healthy and diseased aortic walls, as well as various tissue types within the wall and thrombus. A third study investigated methods for determining material behavior. An existing inverse in vivo material identification method was fundamentally revised to determine parameters of a hyperelastic and anisotropic material model. The new method is approximately seven times faster and accounts for the thrombus, making it applicable to almost all clinically relevant AAA cases. After in vitro validation on a porcine aorta, in vivo validation compared preoperatively identified material parameters with those from uniaxial tensile tests on ex vivo tissue samples from two AAA patients, showing good agreement. This thesis thus advances the development of patient specific biomarkers to assess acute rupture risk in AAA patients clinically. It strengthens the potential of 4D ultrasound as a non invasive technique for high resolution quantification of structural vessel wall changes. Combining local deformation analysis and material identification opens new perspectives for understanding disease progression and improving clinical decision making and patient outcomes.","abstract_html":"An abdominal aortic aneurysm (AAA) is a permanent local dilatation of the human abdominal aorta, posing a severe health risk due to a rupture related mortality rate of up to 85 percent. Current clinical risk assessment relies on a population derived threshold value for the maximum aneurysm diameter. However, this global metric ignores local tissue alterations from remodeling processes affecting the biomechanical properties of the vessel wall. These changes create heterogeneous deformations and vulnerable regions prone to rupture. Consequently, the diameter based criterion allows limited individual risk stratification, risking unnecessary surgeries or missed critical cases. Currently, no clinically established patient specific biomarker reliably predicts rupture risk. This work focuses on developing and validating non invasive, in vivo applicable methods to characterize the elastic properties of different AAA tissue regions. Additionally, it pursues material behavior identification using a hyperelastic and anisotropic material model. The goal is to provide patient specific markers alongside the diameter criterion to assess individual rupture risk. The central measurement technique is high resolution 4D ultrasound (3D and time) combined with speckle tracking (4D US), enabling spatially and temporally resolved assessment of local wall deformations. The first study developed a method to improve the reliability of single ultrasound acquisitions, reflecting current clinical standards. A comprehensive analysis approach combined multiple estimates of wall deformation from a single acquisition into an averaged model. Using in vivo data from 10 AAA patients, strains were calculated in wall regions with structurally different properties, such as calcifications. The ability to distinguish these regions using 4D US indicates sufficient resolution to differentiate potentially rupture prone regions from more stable areas. Using the averaged models, all patients could be significantly distinguished based on circumferential strain compared to only 25 percent using individual measurements. This enables reliable individual level statements for the first time. The second study extended the focus to thrombotic regions using data from an animal study involving ten apolipoprotein E deficient mice. By comparing in vivo findings with histological cross sections, a new method assigned measured wall strains to five different tissue regions within the vessel wall and thrombus areas. The analysis demonstrated that 4D US can reliably differentiate between healthy and diseased aortic walls, as well as various tissue types within the wall and thrombus. A third study investigated methods for determining material behavior. An existing inverse in vivo material identification method was fundamentally revised to determine parameters of a hyperelastic and anisotropic material model. The new method is approximately seven times faster and accounts for the thrombus, making it applicable to almost all clinically relevant AAA cases. After in vitro validation on a porcine aorta, in vivo validation compared preoperatively identified material parameters with those from uniaxial tensile tests on ex vivo tissue samples from two AAA patients, showing good agreement. This thesis thus advances the development of patient specific biomarkers to assess acute rupture risk in AAA patients clinically. It strengthens the potential of 4D ultrasound as a non invasive technique for high resolution quantification of structural vessel wall changes. Combining local deformation analysis and material identification opens new perspectives for understanding disease progression and improving clinical decision making and patient outcomes.","abstract_has_math":false,"creators":["Hegner, Achim Maximilian Claus"],"institution":null,"degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":["Gámez López, Antonio Juan","Huss, Armin"],"committee_chairs":[],"committee_members":[],"year":2026,"date_issued":"2026","date_published":"2026","updated_at":"2026-07-24T01:29:38Z","subjects":[],"languages":["eng"],"rights":["Attribution-NonCommercial-NoDerivatives 4.0 Internacional"],"rights_urls":["http://creativecommons.org/licenses/by-nc-nd/4.0/"],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/10498/39996","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Gámez López, Antonio Juan","Huss, Armin"]},{"key":"dc:contributor.other","label":"Dc Contributor Other","values":["Ingeniería Mecánica y Diseño Industrial"]},{"key":"dc:creator","label":"Author","values":["Hegner, Achim Maximilian Claus"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2026-07-10T08:15:59Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2026-07-10T08:15:59Z"]},{"key":"dc:date.issued","label":"Date","values":["2026"]},{"key":"dc:type","label":"Dc Type","values":["doctoral thesis"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["Attribution-NonCommercial-NoDerivatives 4.0 Internacional"]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://creativecommons.org/licenses/by-nc-nd/4.0/"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/10498/39996"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["An abdominal aortic aneurysm (AAA) is a permanent local dilatation of the human abdominal aorta, posing a severe health risk due to a rupture related mortality rate of up to 85 percent. Current clinical risk assessment relies on a population derived threshold value for the maximum aneurysm diameter. However, this global metric ignores local tissue alterations from remodeling processes affecting the biomechanical properties of the vessel wall. These changes create heterogeneous deformations and vulnerable regions prone to rupture. Consequently, the diameter based criterion allows limited individual risk stratification, risking unnecessary surgeries or missed critical cases. Currently, no clinically established patient specific biomarker reliably predicts rupture risk. This work focuses on developing and validating non invasive, in vivo applicable methods to characterize the elastic properties of different AAA tissue regions. Additionally, it pursues material behavior identification using a hyperelastic and anisotropic material model. The goal is to provide patient specific markers alongside the diameter criterion to assess individual rupture risk. The central measurement technique is high resolution 4D ultrasound (3D and time) combined with speckle tracking (4D US), enabling spatially and temporally resolved assessment of local wall deformations. The first study developed a method to improve the reliability of single ultrasound acquisitions, reflecting current clinical standards. A comprehensive analysis approach combined multiple estimates of wall deformation from a single acquisition into an averaged model. Using in vivo data from 10 AAA patients, strains were calculated in wall regions with structurally different properties, such as calcifications. The ability to distinguish these regions using 4D US indicates sufficient resolution to differentiate potentially rupture prone regions from more stable areas. Using the averaged models, all patients could be significantly distinguished based on circumferential strain compared to only 25 percent using individual measurements. This enables reliable individual level statements for the first time. The second study extended the focus to thrombotic regions using data from an animal study involving ten apolipoprotein E deficient mice. By comparing in vivo findings with histological cross sections, a new method assigned measured wall strains to five different tissue regions within the vessel wall and thrombus areas. The analysis demonstrated that 4D US can reliably differentiate between healthy and diseased aortic walls, as well as various tissue types within the wall and thrombus. A third study investigated methods for determining material behavior. An existing inverse in vivo material identification method was fundamentally revised to determine parameters of a hyperelastic and anisotropic material model. The new method is approximately seven times faster and accounts for the thrombus, making it applicable to almost all clinically relevant AAA cases. After in vitro validation on a porcine aorta, in vivo validation compared preoperatively identified material parameters with those from uniaxial tensile tests on ex vivo tissue samples from two AAA patients, showing good agreement. This thesis thus advances the development of patient specific biomarkers to assess acute rupture risk in AAA patients clinically. It strengthens the potential of 4D ultrasound as a non invasive technique for high resolution quantification of structural vessel wall changes. Combining local deformation analysis and material identification opens new perspectives for understanding disease progression and improving clinical decision making and patient outcomes."]},{"key":"dc:format","label":"Dc Format","values":["application/pdf"]},{"key":"dc:title","label":"Title","values":["Development and Validation of Non-Invasive Methods for the Identification of Patient-Specific Hyperelastic and Anisotropic Material Properties of Abdominal Aortic Aneurysms In Vivo"]}]}],"canonical_facts":{"dc:contributor.advisor":["Gámez López, Antonio Juan","Huss, Armin"],"dc:contributor.other":["Ingeniería Mecánica y Diseño Industrial"],"dc:creator":["Hegner, Achim Maximilian Claus"],"dc:date.accessioned":["2026-07-10T08:15:59Z"],"dc:date.available":["2026-07-10T08:15:59Z"],"dc:date.issued":["2026"],"dc:description.abstract":["An abdominal aortic aneurysm (AAA) is a permanent local dilatation of the human abdominal aorta, posing a severe health risk due to a rupture related mortality rate of up to 85 percent. Current clinical risk assessment relies on a population derived threshold value for the maximum aneurysm diameter. However, this global metric ignores local tissue alterations from remodeling processes affecting the biomechanical properties of the vessel wall. These changes create heterogeneous deformations and vulnerable regions prone to rupture. Consequently, the diameter based criterion allows limited individual risk stratification, risking unnecessary surgeries or missed critical cases. Currently, no clinically established patient specific biomarker reliably predicts rupture risk. This work focuses on developing and validating non invasive, in vivo applicable methods to characterize the elastic properties of different AAA tissue regions. Additionally, it pursues material behavior identification using a hyperelastic and anisotropic material model. The goal is to provide patient specific markers alongside the diameter criterion to assess individual rupture risk. The central measurement technique is high resolution 4D ultrasound (3D and time) combined with speckle tracking (4D US), enabling spatially and temporally resolved assessment of local wall deformations. The first study developed a method to improve the reliability of single ultrasound acquisitions, reflecting current clinical standards. A comprehensive analysis approach combined multiple estimates of wall deformation from a single acquisition into an averaged model. Using in vivo data from 10 AAA patients, strains were calculated in wall regions with structurally different properties, such as calcifications. The ability to distinguish these regions using 4D US indicates sufficient resolution to differentiate potentially rupture prone regions from more stable areas. Using the averaged models, all patients could be significantly distinguished based on circumferential strain compared to only 25 percent using individual measurements. This enables reliable individual level statements for the first time. The second study extended the focus to thrombotic regions using data from an animal study involving ten apolipoprotein E deficient mice. By comparing in vivo findings with histological cross sections, a new method assigned measured wall strains to five different tissue regions within the vessel wall and thrombus areas. The analysis demonstrated that 4D US can reliably differentiate between healthy and diseased aortic walls, as well as various tissue types within the wall and thrombus. A third study investigated methods for determining material behavior. An existing inverse in vivo material identification method was fundamentally revised to determine parameters of a hyperelastic and anisotropic material model. The new method is approximately seven times faster and accounts for the thrombus, making it applicable to almost all clinically relevant AAA cases. After in vitro validation on a porcine aorta, in vivo validation compared preoperatively identified material parameters with those from uniaxial tensile tests on ex vivo tissue samples from two AAA patients, showing good agreement. This thesis thus advances the development of patient specific biomarkers to assess acute rupture risk in AAA patients clinically. It strengthens the potential of 4D ultrasound as a non invasive technique for high resolution quantification of structural vessel wall changes. Combining local deformation analysis and material identification opens new perspectives for understanding disease progression and improving clinical decision making and patient outcomes."],"dc:format":["application/pdf"],"dc:identifier.uri":["http://hdl.handle.net/10498/39996"],"dc:language.iso":["eng"],"dc:rights":["Attribution-NonCommercial-NoDerivatives 4.0 Internacional"],"dc:rights.uri":["http://creativecommons.org/licenses/by-nc-nd/4.0/"],"dc:title":["Development and Validation of Non-Invasive Methods for the Identification of Patient-Specific Hyperelastic and Anisotropic Material Properties of Abdominal Aortic Aneurysms In Vivo"],"dc:type":["doctoral thesis"]},"updated_at":"2026-07-24T01:29:38Z"}