Research On Real-time Medical Ultrasound Navigation And Soft Tissue Modeling

The ultrasound guided puncture, in which the trajectory and the motion of biopsy needles is visualized in the ultrasound image in real-time, can provide the basis for the puncture path selection. Thus, it is a very important tool in the ultrasound-assisted treatment of diagnosis or therapy, and has a bright prospect. However, there are some shortcomings in the existing ultrasound guided puncture procedures, including the complexity of operation, difficulties in positing the needle precisely, and the inflexible of the puncture angle, etc., as a result, the success of ultrasound guided puncture are still largely depends on the physicians'experiences, punctures failure often happens and it often takes a long time to train new doctors. In response to these issues, a free path ultrasound puncture navigation methods based on electromagnetic positioning is proposed. The soft tissue deformation, which is the key factor of the puncture accuracy, is analyzed using the finite element method (FEM). And the free path puncture navigation method is implemented to a portable ultrasound imaging system. This thesis mainly focuses on:1) Development of the ultrasound puncture navigation algorithm. According to the clinical applications of the ultrasound puncture navigation system, various positioning methods were compared. The electromagnetic positioning method was selected since its features of accuracy in positioning, compact in size, and light in weight. Base on the lab made portable medical ultrasound imaging device, a real-time navigation algorithm was developed, which composed of a mathematical model for different coordinates'transformation and a method for calibrating different coordinates, providing the puncture with information about the position and orientation of needle relative to the ultrasound image plane to improve puncture accurate and reduce the time of puncture.2) Building the soft tissue deformation model using the finite element method (FEM). De-formation of the soft tissue is the most important factor of puncture accuracy, thus, it is very important to study the deformation of soft tissue during puncture. The soft tissue was discretized into a mesh of units using FEM. Then, the linear elastic model of each discrete unit was built based on the analysis of stress and strain in each unit. According to the theoretical model, ANSYS was used to simulate the soft tissue deformation by choosing a tissue geometry represented by a mesh of elements and nodes, selecting a function to describe the relationship between external forces applied to the nodes. It is found that the deformation model can provide reliable warning for puncture navigation systems.3) Integral design of the free path ultrasound guided puncture system. Based on the lab made digital portable ultrasound imaging device, ARM-FPGA dual-core processors and electromagnetic positioning system are used as the hardware of the system. ARM is mainly responsible for the real-time control, such as key touch responding, application software selecting, and FPGA control, while the FPGA is mainly responsible for the information collection and the processing of ultra-sound images, probe control, image storage. The message-driven method is implemented in the design of the software architecture, which can ensure the operating efficiency of the code.