Research On Intravascular Ultrasound Array Imaging-Eccentric Cylinder Wave Compounding And Lateral Deconvolution

Intravascular Ultrasound(IVUS)is a diagnostic method that could image cardiovascular precisely.It can provide a tomographic view of vascular by using a miniature ultrasound transducer placing in the vascular.The shape of the vascular and the distribution of different tissue can be obtained in the image,which can help doctors diagnose precisely.In order to further improve imaging quality,in this thesis we studied two aspects of IVUS.The IVUS array systems cannot perform all-depth focusing with a high signal-to-noise ratio(SNR),to solve the problem,we proposed eccentric cylinder wave compound imaging technique(ECWC),improving SNR via improving the energy emitted into the tissue.We analyzed the principles of multi-emission-wave-compounding techniques,and concluded some key factors that would affect the quality of imaging,these conclusions work as guidance in the optimization of imaging parameters.We proposed the specific procedures of ECWC and found the best parameters for imaging,the feasibility of the procedures was examined in simulation.The results show similar resolution as phased array imaging,and the best SNR among ECWC,phased array imaging,and synthetic phased array imaging.Practical factors such as cross-talk and non-uniform array elements were analyzed and the results show that the impact is limited.Dual apodization was applied to suppress the grating lobes,particle swarm optimization was applied to determine the apodization function.Phased array IVUS catheters can be modified slightly to perform ECWC.The lateral resolution of IVUS systems is lower than axial resolution,we proposed magnitude-based non-negative domain deconvolution to improve lateral resolution.This method avoids the amplification of high frequency noise by inverse filter via the limitation of the solution domain to be non-negative,and thus omitting the operation of noise suppression that would impede the improvement of resolution.We first analyzed the suppression of noise in normally used deconvolution methods,and points out that the suppression is in sacrifice of resolution,and based on which we proposed our method.We did simulation to examine the method and discerned 70 ?m separated scatterers with a transducer with 120 ?m lateral resolution.The simulation results show that the method can provide 50%better resolution than Wiener deconvolution.We built a single transducer-mechanical scanning experiment system to further examine the method,2° lateral resolution can be realized in far field,and the resolution degraded in near field because of the spreading out of the lateral point spread function.The experiment on a phantom shows the ability of the method to improve resolution in complicated practical environment.Results from our study show that implementing ECWC and magnitude-based non-negative domain deconvolution on IVUS array systems can yield high quality and high resolution images.