Study On Coherent Plane Wave Compounding Technology In Medical Ultrasound System

Medical ultrasound imaging technology is an important tool which is widely used in clinical practice and treatment evaluation.The coherent plane wave compounding algorithm coherently superimposes different plane wave images,which can improve the image quality,but will increase the processing time,resulting in a decrease in the frame rate.The implementation of coherent plane wave compounding algorithm on FPGA can improve the image quality and reduce the processing time.In order to reduce the cost of hardware implementation,sign coherence factor is selected to realize the coherent superposition of plane wave images,and the simulation study on the imaging effect of the algorithm is conducted.The hardware design scheme of the coherent plane wave compounding algorithm is further proposed,and the imaging test and analysis of the scheme is carried out based on the 64×64 phase array platform.The simulation study of the coherent plane wave compounding algorithm based on the sign coherence factor is conducted with the Field-II ultrasound simulation platform.The resolution and contrast of the algorithm are tested by setting a point target phantom and a cyst phantom.Simulation results show that the algorithm can improve the resolution and contrast of plane wave images and suppress side lobes.By analyzing the principle of coherent plane wave compounding algorithm and sign coherence factor,a hardware design scheme of the coherent plane wave compounding unit based on FPGA is proposed.According to the modular design principle,the coherent plane wave compounding unit is divided into echo data control module,sound path calculation module,pixel data processing module and image compounding control module.The echo data control module realizes the storage and extraction of echo data through a 64-channel parallel structure.The calculation of transmit sound path and receive sound path is implemented by CORDIC algorithm and Square Root IP core respectively.The pixel data processing module realizes the calculation of the sign coherence factor by look-up table,and ensures the timing performance by reducing the computational complexity.The image compounding control module uses a single RAM to realize the dynamic superposition of multiple plane wave images,which reduces the consumption of storage resources.The coherent plane wave compounding unit adopts a pipelined architecture and can process one pixel data per clock cycle.The imaging test of the coherent plane wave compounding unit is carried out based on the64×64 phase array platform.The test results show that the compounding image output by the coherent plane wave compounding unit can improve resolution,and the lateral and axial resolution are improved by about 48.9% and 10% respectively.The speckle target in the image has a clear boundary,and the contrast can be improved by about 56.7%.When the number of pixels is set to 256×256 and the number of plane wave images is set to 11,the frame rate of the coherent plane wave compounding unit can reach 129.8 fps,which meets the requirements of clinical diagnosis.The coherent plane wave compounding unit based on FPGA can improve the imaging quality while ensuring the frame rate.