Research On Synthetic Focusing Ultrasound Imaging

Ultrasonography is an important imaging diagnosis method and has been widely used in medical field.As an image reconstruction technology,synthetic aperture ultrasonic imaging derives from radar synthetic aperture technology,which composites sub-apertures into full aperture.The synthetic focusing method can achive higher resolution than other imaging methods using the same transducer.Synthetic focusing is one of the synthetic aperture techniques,it can achieve fully dynamic focusing in both transmit and receive events,obtaining extremely high and uniform resolution.Furthermore,synthetic focusing method can reconstruct an image from one transmit event,having potential in fast ultrasonography.This thesis focuses on the realization of synthetic focusing imaging,the mode of which is single element emission full aperture receiving,and puts forward two imaging methods.The process from raw radio frequency data acquisition to image is introduced in detail.The imaging results for traditional ultrasound imaging method and synthetic focusing method will be compared.Based on the two synthetic focusing imaging methods,how to improve imaging speed is analyzed from two aspects,emission time and echo data processing time.This thesis also introduces the experimental data acquisition platform and how to acquire data.For every emission,an echo data set is acquired.After all elements transmit,complete data set is obtained.For echo data,there are two processing methods.The first one is reconstructing a low-resolution image for every echo data set,then combining these low-resolution images into a high-resolution image,named image superposition based synthetic focusing method.The second one is directly making a high-resolution image using all echo data,named signal superposition based synthetic focusing method.In addition to regular procedures such as beamforming,envelope detection,signal range adjustment,this thesis uses baseline calibration procedure for baseline shift.Plane wave imaging is introduced as a classical fast ultrasonography method for comparison.In conclusion,this thesis introduces how to realize synthetic focusing imaging,discusses the optimization of both image quality and imaging speed,displays the experimental results of phantom data and human carotid artery data.The experimental results of phantom data show that the lateral resolution for synthetic focusing method has greatly improved compared with the traditional ultrasound imaging method,and the resolution decreases slightly with the increase of imaging depth.