Abstract
Increased arterial thickness measured with ultrasound correlates with future cardiovascular events, but conventional ultrasound imaging techniques cannot distinguish between intima, media, or atherosclerotic plaque in the carotid artery. In this work, we evaluated how well vascular elastography can detect intimal changes in a mouse model of carotid remodeling. We ligated the left external and internal branches of the carotid artery of male FVB mice and performed sham operations for 2 weeks. High-resolution ultrasound imaging accurately detected lower blood velocities and low blood volume flow in the carotid arteries after ligation in FVB mice. However, ultrasound could not detect differences in the carotid wall even at 2 weeks post-surgery. The Young’s modulus was measured based on displacements of the carotid artery wall, and Young’s modulus was 2-fold greater in shams at 1 week post ligation, and 3-fold greater 2 weeks after ligation. Finally, the higher Young’s modulus was most associated with higher intimal thickness but not medial or adventitial thickness as measured by histology. In conclusion, we developed a robust ultrasound-based elastography method for early detection of intimal changes in small animals.
Highlights
Diagnostic ultrasound can assess the progression of vascular disease in patients[1], but further improvements are needed
Diastolic and systolic lumen diameters of the ligated left carotid artery (LCA) were similar or even greater in size compared with shams, but lower than in contralateral right carotid artery (RCA) over the 2-week time period (Table 1). 3D imaging of the LCA after ligation showed significant reduction of the carotid lumen volume (Fig. S1B; Fig. 1B)
The calculated shear stress was consistently reduced in the ligated LCA but normalized in the RCA after ligation (Fig. 1E; Fig. S1E)
Summary
Diagnostic ultrasound can assess the progression of vascular disease in patients[1], but further improvements are needed. It is difficult to detect preclinical atherosclerosis or classify different plaque components[6] with standard ultrasound This limitation occurs because – except for calcification – ultrasound backscatter signal strength is independent of plaque composition. Emerging ultrasound techniques such elastography show promise in overcoming these limitations by visualizing changes in the biomechanical properties (stiffness) in the underlying tissues’ different echogenicities. The motivation for conducting this study is that thickening of the intima occurs in the early stages of atherosclerotic process; an imaging system that can detect these early changes would allow clinical researchers to design interventions that can be evaluated in smaller samples and require shorter follow-up to assess effectivity. Our group has developed a mouse model of low flow-induced carotid thickening without atheroma[28], which we will use to study how well vascular elastography can assess structural changes in carotid arteries
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