Research On Key Techniques For Real-time Ultrasound Visualization

Ultrasonic imaging technology is one of the most important medical imaging methods. For the advantages of low costs and no damage to human body, it has a irreplaceable status in clinical diagnosis. In recent years, the development of miniaturization and portable ultrasonic diagnostic equipment has expanded the potential application of ultrasonic imaging in the areas of township medical care, family health care, first aid in battlefield, etc., increasing the requirements of performance in real-time, intuitive ultrasonic visualization. Currently, other than the traditional B mode, M mode and doppler blood flow imaging, the technologies of doppler energy imaging, doppler tissue imaging,3D fetal imaging,3D surface rendering puncture guide, etc., are also main implementation schemes. However, due to the limitation of the algorithm and hardware, widely-used method of volume rendering in the traditional non real-time imaging such as CT, MRI is still difficult to realize with ultrasonic time-varying data. Meanwhile, conflicting with the fact of today’s increasing medical needs, ultrasonic diagnostic equipment is still limited to large hospital medical, which leads to the increasing call of new ideas and solutions. Concerning the key technology of ultrasonic visualization, we combined the FPGA acceleration, cloud computing, etc. to generate a new architecture scheme, which has made the beneficial exploration for real-time3D ultrasonic imaging and nonlocal remote control imaging, and extend the development direction of ultrasonic medical terminal.This dissertation is mainly based on the realization and application of3D and Cloud based ultrasound imaging. Focused researches were carried out on improved volume rendering algorithm, FPGA hardware acceleration of Shear-warp algorithm, distributed ultrasonic imaging based on cloud computing architecture, and EDA design and test methods based on the workstation mode.The main research work and innovational points of this paper are as following:(1) Considering the high requirements of real-time, portability of ultrasound, and insensitivity to image details, specially designed volume rendering algorithm for3D visualization based on hardware acceleration is studied. Improved algorithm based on object space Shear-warp algorithm is proposed, which introduced a new data sequencing method to solve the problem that the one-dimensional data storage format of the real storage device is hard to satisfy3D imaging real-time calculation. The new sequence method can avoid the pretreatment process which is required in the sight spindle adjustment by performing transformation of the data configuration according to specific view direction; on the other hand, the algorithm introduced an optimization to image-sequencing-based Shear-warp algorithm to overcome the key storage bottleneck of volume rendering algorithm and satisfy the timing requirements imposed in the handling of time-varying data in real time by applying the reading sequence of image space in Ray-casting algorithm to the Shear-warp algorithm, as well as combining focused optimization of the bottom layer and real-time computing of specific parameters.(2) Concerning the reconfigurability and logical design flexibility of FPGA, complicated reading and writing of intermediate image cache is avoided by making use of the FPGA hardware acceleration for improved Shear-warp algorithm and perfoming highly parallel processing architecture and real-time calculation for pipeline parameters. The ultrasonic time-varying data processing is realized based on Xilinx Company’s Virtex series high performance FPGA, where new methods of implementation of address calculation and storage control are put forward as well. Specifically, in address computation, a front-end address written calculation method different from the traditional back-end one is introduced, where real-time reading and writing address of3D image would be calculated according parameters, and the internal storage pressure would be transferred to logical calculation pressure through realizing Shear translation by FIFO-shift-enabled adjustment of the cache location, which would also effectively reduce the resource consumption; In terms of storage control, because of the high demand of the real-time system, a strategy of multi-stage cache of the intermediate image is utilized based on the sight-line sequencing, which build double RAM for shallow lines cache to achieve a ping-pong operation, improving the synchronization performance of the assembly line effectively. Independently designed special floating-point accumulator is applied in order to realize the highly pipelining data processing, which can reach an80FPS frame rate for256X256X2563D image data processing of variable address with the system clock being100MHZ, in other words, realized the implement of the time-varying data volume rendering in real-time imaging.(3) Due to high dependence of the ultrasonic imaging mode to the front-end probe, frequent application oriented targeted optimization is needed. This paper set up an integrated digital ultrasound ultrasonic imaging testing platform, introduced the logical system design method on the basis of the ISE and ModelSim workstation, and reduced development cycle for reconstruction of the system under different applications. Embedded FPGA ultrasonic visualization verification test platform is implemented by maintaining user IP extension on the basis of common2D ultrasound imaging. The volume rendering imaging realized in the third chapter is tested by importing user’s IP into embedded system structure. Comparison between test results of different algorithms and the standard image is carried out proving the practicality of the FPGA based Shear-warp volume rendering in the field of ultrasonic.(4) A wide-area medical model and a solution of distributed ultrasonic imaging based on cloud computing is proposed, where the ultrasonic devices are specially simplified by only remaining the front-end acquisition and processing and transferring the image storage and processing, such as high performance algorithm implementation to the cloud-end, which implements the embedded ultrasonic terminal cloud computing. Remote consultation is realized through real-time3D data accessing and rendering by CMUT and diffraction wave imaging through cloud computing ultrasonic system, volume rendering image output by making use of the MicroBlaze soft nucleus and portable operating system μC/GUI implementation, process the results storage through the DICOM store format and uploading to the cloud server, and finally consultation by meaning of adjusting parameters such as Angle of volume rendering, opacity lookup table through commands received by the cloud-end. Facing the bandwidth limitations for the cloud mode, a solution is designed where3D visualization is integrated into the front end, and a remote two-way control strategy are studied.