| BackgroundCardiovascular disease is a major cause of mortality and morbidity throughout the world. The leading causes of acute ischemia cardio-cerebrovascular diseases, so the early detection of vulnerable atherosclerotic plaques to prevent the occurrence of heart cerebrovascular accident is of great importance. As carotid artery can be a window to watch the atherosclerosis physically, checking means of the morphological characteristics and vulnerability of carotid atherosclerotic plaques have become a clinical hot spot.In recent years, studies have found that plaque rupture depends on vulnerability of atherosclerotic plaques. Current researches suggest that the morphological features of vulnerable plaques include:big lipid core, thin fibrous cap (<65 microns), a large number of inflammatory cells infiltration. Now diagnostic techniques which simply show the lumen or plaque morphology, such as ultrasound, computed tomography (CT) and intravascular ultrasound (IVUS) and Coronary artery angiography (CAG), could not meet the need of Clinical applications. Elasticity is one of the biomechanical parameters affected mostly by the physiological and pathological process. Collagen fibers and smooth muscle in vascular wall and lipid composition with regular structure under normal conditions have regular structure and strict hierarchy. Under atherosclerosis (AS) conditions, the original structure and level of change and lipid and inflammatory activity increased, which lead to the change of the mode of molecular composition and the structure of tube wall tissue, while the change of the mode of molecular composition and the structure of tube wall tissue is the main factor decision organization flexibility. Modulus of elasticity (E) as the basic attributes of elastomer, is the best index to reflect the human tissue elasticity in theory. But due to the stress is not easy to directly measure within the vascular wall, it is very difficult to make the calculation of E. Therefore, the current researches about atherosclerosis plaques mainly focused on strain imaging, but researches about young’s modulus through direct measurement are very few.Elasticity imaging technique is a new imaging method and has extensive application prospect in clinic. The basic principle of elasticity imaging is to impose an internal motivation. In elastic mechanics and biomechanics laws, the motivation will produce a response, such as displacement, strain, velocity distribution. Ultrasonic elastography concludes the static quasi-static compression elasticity imaging, blood vessel elasticity imaging, myocardial elasticity imaging, with the sound of the low-frequency vibration excitation elasticity imaging, and super fast ultrasonic imaging system, based on the pulse of the instantaneous elastic elastic imaging, acoustic radiation imaging or pulse excitation of sound radiation pulse imaging, valley, radiation imaging, shear wave elastography and supersound shear imaging, acoustic emission technology of ultrasonic excitation vibration acoustic imaging and simple harmonic motion imaging. Among them, the shear wave elastography technology (SWE) can quantitatively reflect the local tissue elasticity information, and at present is mainly used in thyroid, breast, liver, prostate, gynecology, muscles and so on. However research about atherosclerosis plaques is less. This research uses the SWE technology to quantitatively measure and analysis the Young’s modulus of different kinds of plaques, and compares with pathologic histology, aiming to analyze the assessment value in identifying the plaque tissue character and vulnerability.Objectives(1) To investigate the accuracy and reproducibility of SWE in CIRS(?) phantoms.(2) To investigate the value of shear wave elasticity imaging (SWE) on characterizing components and identifying the vulnerability of atherosclerotic plaques in vivo on a rabbit model.Methods(1) The accuracy, as well as the inter-and intra-observer variance of quantifying the Young’s modulus by SWE technique was first evaluated with the CIRS(?) phantoms as the golden standard.(2) Animal model was developed by abdominal aorta endothelium denudation and high-cholesterol diet for 24 weeks on 20 purebred New Zealand rabbits. SWE images of atherosclerotic plaques found in the abdominal aortas were acquired in situ to acquire the Young’s modulus. Then the plaques were harvested and matched with the distance between the right renal artery and the plaques recorded during SWE imaging.(3) Histological slices were stained for fat, collagen, smooth muscle cells (SMCs) and macrophages by Oil O red, picric Sirius red, Von kossa stain and anti-a-SMC, anti-RAM-11 immunohistology. Vulnerability index were also calculated as the percentage of (macrophage+ fat)/(smooth muscle cell+ collagen). The correlation between the Young’s modulus and plaque components and vulnerability index were analyzed. The value of SWE on differentiating plaque types was evaluated by ROC analysis.Results(1) High agreement was found between the estimated Young’s modulus by SWE and the gold standard. The coefficient of variant of inter-and intra-observer was very low at the range of 1.0%-3.8%.(2) The maximal Young’s modulus obtained by SWE correlated positively with collagen, SMC and calcification (r= 0.567,0.561 and 0.574, respectively with P<0.001), and negatively with fat and macrophage infiltration (r=-0.543 and -0.482, respectively with P<0.005). The mean Young’s modulus also correlated positively with collagen and SMC (r=0.532,0.558 and 0.566, respectively with P<0.05), and negatively with fat and macrophage (r=-0.527 and -0.421, respectively with P<0.05). Both the maximal and the mean Young’s modulus correlated negatively with the vulnerable index (r=-0.620 and -0.619, respectively with P<0.001).(3) ROC analysis revealed high sensitivity (85%) and specificity (80%) for differentiating fatty plaques from fibro-fatty plaques by Young’s modulus.Conclusions(1) SWE technique can be used for estimation of the young’s modulus of atherosclerotic plaques with high accuracy and reproducibility.(2) Good correlation is evidenced between the Young’s modulus and plaque components and vulnerability. Fatty and fibro-fatty plaques can be differentiated by Young’s modulus with high sensitivity and specificity. Thus, SWE technique is promising for identifying vulnerable plaques. |
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