Towards non‐invasive in vivo characterization of the pathophysiological state and mechanical wall strength of the individual human AAA wall based on 4D ultrasound measurements

Abstract

Abdominal aortic aneurysms (AAA) are a degenerative disease of the aorta with high associated mortality. Currently, there is a lack of in vivo information, which allows to characterise the individual aneurysmal wall with regard to wall strength or rupture risk. We have used 4D ultrasound strain imaging to compute the spatially resolved distribution of the in-plane strain tensor and of the local distensibility in three patient groups (young, < 40 y. o.; elderly, > 60 y. o.; AAA). Mean and local maximum deformation and distensibility as well as indices for the local variations of the strain and the distensibility distribution were determined. Mean distensibility is significantly decreasing from young (3.83 [2.83, 5.87] 10 −3 mmHg −1 ) to elderly (0.67 [0.39, 0.87] 10 −3 mmHg −1 ) and AAA (0.27 [0.20, 0.54] 10 −3 mmHg −1 ). Both indices characterising the heterogeneous elastic behaviour are significantly increasing from young through elderly to AAA. Linear dependency of some of the distensibility distribution indices on age and aortic diameter was observed in the young and elderly group.In contrast, none of the indices depended on age or maximum diameter in the AAA group. We hypothesize that the heterogeneous distensibility distribution is indicative of microstructural changes in the aortic and aneurysmal wall and might contribute to a more complete and informative pathophysiological characterisation of the AAA wall, either with respect to wall strength or rupture risk. To confirm this hypothesis, further studies will be necessary in which the correlation between the proposed indices and individual wall strength and rupture risk is tested. K E Y W O R D Sabdominal aortic aneurysm, in vivo, local distensibility, spatial heterogeneity INTRODUCTIONAn abdominal aortic aneurysm (AAA) is a degenerative disease of the aorta, which is characterised by a permanent local dilatation of the aorta. AAA occur with a rate between 1.3% and 8.9% in men over 60 y.o. and 2.2% in women. [1,2] The main risk of this mostly asymptomatic disease is the rupture of the aneurysmal wall [3] with associated mortality rates of 53.1% in the US, 65.9% in the UK, [4] and 48% in men and 39% in women in Germany. [5] Currently, the clinical indications for surgical or endovascular treatment are a maximum AAA diameter larger than 5 cm in women and 5.5 cm in men or a growth rate of

Intra‐ and Interobserver Variability of 4D Ultrasound Examination of the Infrarenal Aorta

“…The cyclic registration of strain amplitude of all speckles with the temporal resolution of 22–26 frames/s enabled the precise definition of diastolic and systolic aortic diameters and patient‐specific strain. The circumferential strain was chosen as the most significant parameter for the investigation of 4D‐US reliability 8,7 …”

“…However, the introduction of real‐time 3D speckle‐tracking ultrasound (4D‐US) enables the imaging of the entire aortic segment and thus the simultaneous determination of the longitudinal and circumferential expansion 5 . In comparative studies, the age‐related and pathology‐specific changes in the strain pattern in the infrarenal aorta were demonstrated 6 and characterized by corresponding changes in distensibility 7 . The use of 4D‐US provides information about the geometry of the aorta and local deformation of the aortic wall during the heart cycle.…”

A machine leaning approach for abdominal aortic aneurysm severity assessment using geometric, biomechanical, and patient-specific historical clinical features

“…Abdominal aortic aneurysm (AAA) is an irreversible expansion of the infra-renal aorta at least 1.5 times of a healthy aortic diameter. In light of its high mortality rate, this condition is becoming one of the leading causes of death worldwide [1][2][3]. The current clinical guidelines consider only the maximum transverse diameter (D max ) of AAA (5.5 cm for men, and 5 cm for women) to monitor abdominal aortic aneurysm (AAA) severity, risk of rupture, and need for repair [4,5].…”

“…Moreover, it has been shown that in addition to geometric indices such as D max , a variety of biomechanical parameters and material properties affect AAA morphology and behavior [3,[7][8][9]. Wall stress distribution and mainly the peak wall stress -which is directly related to the failure site on the AAA surface -computed using finite element analysis (FEA) have been helpful to comprehensively consider the effects of all mentioned parameters [10][11][12].…”

Preface of the special issue on mathematical and computational modeling in biomechanics

“…The application of such computational modeling in a clinical context requires, of course, patient‐specific information about the mechanical properties of aneurysmal tissue. The paper [] points out in detail how such information can be obtained non‐invasively and at an acceptable cost by means of ultrasound techniques. Not only cardiovascular diseases but also cancer biomechanics have great promise as a source of ideas for future optimized treatments.…”