Research On Intravascular Ultrasonic Elastography Based On Dual Frequency Ultrasonic Transducer

Atherosclerosis(AS)is one of the most common vascular diseases in clinical practice.Cerebral infarction,coronary heart disease,aneurysm and other diseases caused by it seriously endanger human health.In particular,coronary heart disease has become the first killer threatening human life.It is mainly found in the abdominal aorta,coronary artery,carotid artery and other arteries.The accumulation of atherosclerotic plaques in the artery intima will cause thickening of the arterial wall and narrowing of the vascular lumen,resulting in blockage or even rupture of the blood vessel.The mechanical properties of atherosclerotic plaque are related to the vulnerability of plaque.How to effectively monitor the mechanical properties of plaques is one of the important methods for clinical identification of plaque tissue and diagnosis of disease stages.Recently,elastography has been widely used in the evaluation of soft tissue mechanical properties.An external force is transmitted to the body,causing the deformation of the tissue in a specific area,then,the deformation of tissues in the area with different mechanical properties was detected and distinguished through specific methods.Elastography can map the biomechanical properties of biological tissue.Therefore,elastography can be used to identify plaques in blood vessels,especially vulnerable plaques.It is one of the primary techniques for clinicians to diagnose and confirm the stage of atherosclerotic disease.Lowfrequency ultrasound is always used as the excitation and detection method for traditional noninvasive ultrasound elastography,which could ensure sufficient energy to act on the tissue for deep penetration depth.However,the low-frequency ultrasound would decrease the resolution of images,making it difficult to identify tiny plaques,which limits the clinical application in AS.Intravascular ultrasound(IVUS)elastography was investigated to address the characteristics of atherosclerotic diseases.In this study,a dual-frequency IVUS transducer which consists of 10 MHz and 40 MHz elements was designed for acoustic radiation force elastic imaging(ARFI).The 10 MHz focused element was used to generate sufficient acoustic radiation force(ARF),meanwhile,the 40 MHz imaging element was applied to detect the displacement of biological tissue caused by ARF.While ensuring enough energy to act on the tissue,the high-resolution image of plaque tissue could be obtained.Through the parallel compact layout design,the outer diameter of the dual-frequency IVUS transducer is only 1.55 mm.A dual-frequency IVUS elastography system was built based on the designed dualfrequency IVUS transducer.The corresponding system synergistic framework,and the rotational structure between IVUS transducer and motor were designed.Meanwhile,the upper computer data acquisition and processing program was compiled with Lab View according to the system workflow.The ultrasound elastography algorithm was written with the normalized cross-correlation algorithm and the Loupas algorithm.The advantages and disadvantages of the two algorithms were compared to realize the estimation of tissue displacement.The algorithm was improved involve with the characteristics of ultrasound echo,and the parallel acceleration of algorithm processing was realized by using GPU based on CUDA,which greatly improved the processing speed.Finally,customized phantoms with different hardness were used to verify the feasibility based on the designed system.The influence of different parameters on tissue displacement was studied and the elastography results of different phantom models was given.High resolution IVUS elastic images was realized with a resolution of 369 μm.Compared with the measured Young’s modulus,this method can provide young’s modulus for reference.The results of phantoms experiments preliminarily verify the feasibility of the method.Furthermore,in vitro porcine coronary artery and in vivo rabbit abdominal aorta were experimented,obtaining the ultrasound elastography images of the blood vessel wall tissue with different hardness.The results demonstrated that the ultrasonic elastography method using dual-frequency intravascular ultrasonic transducer is feasible for detecting atherosclerotic plaque.This paper has made a breakthrough in the in vivo application of dualfrequency IVUS elastography,which provides sufficient diagnostic basis for the detection of clinical atherosclerotic diseases.