Research On Signal Processing Of Fast High-resolution Medical Ultrasound Imaging

Medical ultrasound imaging has become one of the irreplaceable imaging methods in clinical examinations due to its advantages of real-time,flexibility,safety and low cost.Due to the consideration of both time resolution and image resolution,many methods in fast high-resolution medical ultrasound imaging have become hot topics in modern medical ultrasound research,such as coherent plane-wave compounding(CPWC)for ultrafast ultrasound imaging and coded excitation which could improve the signal-to-noise ratio.In order to further improve the diagnostic quality of fast high-resolution medical ultrasound imaging,on the basis of signal processing,this thesis mainly carried out the following work:This thesis proposes a dual-frequency endoscopic ultrasound imaging method based on coded excitation and applies it to the spinal fusion surgery which requires the insertion of pedicle screws.This method uses coded excitation to increase the depth of ultrasound imaging of the pedicle;at the same time,it also combines the respective advantages of high-frequency and low-frequency imaging,and finally futher improves the detail resolution of the nail path.Compared with the clinical ultrasound imaging for guided screw insertion,the method proposed in this thesis has a higher imaging depth and better detail resolution without reducing the frame rate.Thus,it would improve the safety of the spinal fusion surgery.To take full advantage of the RF data for better image quality,this thesis proposes a new united coherence-based factor beamforming framework in spatial domain for CPWC.The frame rate of CPWC is negatively related to the transmitting angle numbers.Thus,in order to enhance its image quality without increasing CPWC's angle numbers,the united framework containing both aperture and angular information was proposed.Based on the results shown in simulation,phantom and in-vivo datasets,the united framework offers significant improvements over the conventional frameworks in lateral resolution and contrast resolution.At the same time,with the help of the united framework,the imaging quality of ultrafast blood flow imaging is also improved.This thesis also proposes a new united bandpass-angular weighting template for beamformers in f-k domain for CPWC.Compared to the conventional Stolt's f-k method and the incorporating angular weighting template,the new united template enhances the image contrast without extra computational load.Considering the relationship between the united template and bandpass filter,this thesis also applies it straightly to the harmonic imaging,which could also further reduce the computational burden of digital signal processing.