Research On Photoacoustic Elatography Based On Shear Wave

Elasticity and viscosity of human tissue are closely related to its physiological and pathological characteristics.A large number of studies have shown that detecting tissue elasticity and viscosity characteristics will help the diagnosis of various diseases.As an effective imaging tool to measure the hardness of soft tissue and study the mechanical properties of soft tissue,elastography has important clinical application value.In the existing elasticity imaging method,ultrasound elastography imaging method performs low resolution,optical coherent penetration imaging method has small penetration depth,and magnetic resonance elastography is expensive and not suitable for the patients who has magnetic metal or pacemaker inside their body.Therefore,it is of great significance to study a non-ionizing,non-invasive elasticity imaging method that can take both imaging depth and imaging resolution into account.Based on photoacoustic imaging and shear wave elasticity imaging method,this paper proposes a photoacoustic elastography method based on shear wave,which is used to get elastography of tissue by detecting shear wave produced by pulse laser.This method can achieve high contrast and high spatial resolution imaging while ensuring the depth of imaging,while quantifying elasticity and viscosity.This method combines with optical coherence tomography has the potential to realize non-contact detection and is helpful to measure the organs that are not suitable for contact detection.In addition,this method can be directly applied to the existing photoacoustic tomography system to realize multi-mode imaging and detect more comprehensive tissue information.This paper analyzes the basic principle of the photoacoustic elastography method based on shear wave,builds a set of photoacoustic elastography system and studies the elasticity reconstruction algorithm.By using the photoacoustic elastography system and reconstruction algorithm based on shear wave,the photoacoustic elastography experiment based on share wave has been conducted on the gelatin phantom,which verify the feasibility and effectiveness of this photoacoustic elastography method proposed in this paper.In this paper,the process that pulse laser excites shear wave is divided into heat conduction and thermoplastic process to be analyzed for principle of imaging method,and simulation model was established by using finite element analysis software to solve and verify the feasibility of this method.An imaging system based on shear wave elastography and photoacoustic elastography system is designed and constructed.The construction of photoacoustic elastography is realized by using displacement estimation method and shear wave speed estimation method.Finally,through photoacoustic elastography experiment performed on the inhomogeneous phantom and homogeneous phantom of different hardness which is compared with the results of ultrasound elastography.The feasibility,effectiveness and spatial resolution of this photoacoustic elastography method is verified.This paper proves that issue irradiated by pulsed laser can produce shear wave through simulation and experimental method,and the shear wave can be detected by the photoacoustic elastography system built in this paper.Using the imaging algorithm to calculate the detected data,the two-dimensional photoacoustic elastic image of the tissue can be obtained,and the elasticity and viscosity of the tissue can be quantitatively analyzed.The experimental result shows that,this paper proposes a photoacoustic elastography method based on share wave can realize elasticity reconstruction of area to a depth of 13.5 mm,which broke the optical diffraction limit,and imaging spatial resolution is 0.4 mm,while the resolution of ultrasound elastography used in this paper for comparison is 0.9 mm.