Bidirectional Ultrasound Elastographic Imaging Framework for Non-invasive Assessment of the Non-linear Behavior of a Physiologically Pressurized Artery |
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Authors: | Yahua Wang He Li Yuexin Guo Wei-Ning Lee |
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Institution: | 2. Medical Engineering Programme, University of Hong Kong, Hong Kong |
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Abstract: | Studies of non-destructive bidirectional ultrasound assessment of non-linear mechanical behavior of the artery are scarce in the literature. We hereby propose derivation of a strain–shear modulus relationship as a new graphical diagnostic index using an ultrasound elastographic imaging framework, which encompasses our in-house bidirectional vascular guided wave imaging (VGWI) and ultrasound strain imaging (USI). This framework is used to assess arterial non-linearity in two orthogonal (i.e., longitudinal and circumferential) directions in the absence of non-invasive pressure measurement. Bidirectional VGWI estimates longitudinal (μL) and transverse (μT) shear moduli, whereas USI estimates radial strain (?r). Vessel-mimicking phantoms (with and without longitudinal pre-stretch) and in vitro porcine aortas under static and/or dynamic physiologic intraluminal pressure loads were examined. ?r was found to be a suitable alternative to intraluminal pressure for representation of cyclic loading on the artery wall. Results revealed that μT values of all samples examined increased non-linearly with εr magnitude and more drastically than μL, whereas μL values of only the pre-stretched phantoms and aortas increased with ?r magnitude. As a new graphical representation of arterial non-linearity and function, strain–shear modulus loops derived by the proposed framework over two consecutive dynamic loading cycles differentiated sample pre-conditions and corroborated direction-dependent non-linear mechanical behaviors of the aorta with high estimation repeatability. |
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Keywords: | Artery Elastography Non-linear Shear modulus Strain Ultrasound |
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