Research On Surgical Instrument Tracking Assisted By Ultrasound Image

As the morbidity of prostate cancer increases each year,the patients become younger,and accurate therapy of prostate cancer attracts more attention.In robotic-assisted laparoscopic radical prostatectomy,surgeons teleoperate the surgical robots with the limited view provided by endoscopic.However,endoscopic images can't show subsurface nerve and blood vessels(NVB)around prostate,which may cause NVB injury during operation,and result in postoperative sexual dysfunction and uracratia.In this paper,we accomplish the registration between the ultrasonic probe operating mechanism and surgical robot by pushing the surgical instruments to tissue.The results are used to realize the tracking of surgical instrument,so ultrasonic images of tissues during operation can be presented in real time.With the help of ultrasonic image,NVB injury can be effectively decreased.Firstly,we designed an ultrasonic probe operating mechanism,and its structure and control system are designed based on the patient position,the shape of probe and the imaging requirement during prostatectomy.By integrating the probe operating mechanism,ultrasonic device and console,we build up an ultrasound image assisted system,and we also make a work flow of system operation procedure.Then,and automatic extraction method is proposed to extract surgical instrument feature point in ultrasonic image.The method can avoid the influence of subjective factors,and therefor has a better extraction accuracy.In the method,modified HAMMER algorithm is firstly used to register images containing surgical instrument with images excluding surgical instrument,and the subtraction method is then adopted to get a rough contour.Afterwards,the proposed anisotropic diffusion method combined with J divergence is exerted on the images.Finally,we propose an improved parametric active contour method,which takes the subtraction contour as the initial contour,and calculates the global optimized surgical instrument profile.By calculating the average value of coordinates in result region,feature point of surgical instrument is finally acquired.Next,to get the intrinsic and external parameters,we use classical N-type board to calibrate the ultrasonic probe.With these parameters,we can acquire feature point coordinates in probe operating mechanism coordinate system and surgical robot coordinate system.Afterwards,the Levenberg-Marquardt algorithm is used to complete registration between probe operating mechanism and surgical robot.Based on above results,we can realize the tracking using kinematic deductions.Finally,we conduct a series of experiments to test the ultrasound image assisted system.Combined with surgical robot,an ultrasound image assisted surgical robot platform is built up.Based on the platform,we verify the feature point automatic extraction method.Testing results show that the automatic extraction method has superior accuracy and stability.With probe calibration experiment and probe operating mechanism registration experiment,we obtain calibration parameters and registration parameters.With these parameters,the tracking experiments are conducted,and results can verify the availability of tracking technology.