Ultrasonic sensor system for measuring position and orientation of laproscopic instruments in minimal invasive surgery

In minimal invasive surgery usually an endoscope is used to show the surgeon what is happening inside the human body. However, this view is very limited and gives no information of instrument positions outside the camera view. A new positioning system is proposed that should give the surgeon the exact location and orientation of the instruments in the patient. The measuring system consists of markers placed on the instruments, outside of the human body. Knowing the dimensions of the usually rigid instruments it is possible to calculate their position and orientation inside the human body from the marker positions. Two pairs of ultrasound markers placed on each instrument will suffice to measure both the position and orientation. The detection of marker positions is realized by an array of ultrasound receivers. The influence of variations in temperature, humidity and pressure of air on the phase-shift and time-of-flight methods was investigated. Using the time of flight method, the variations of distance and time of flight have a linear correlation and it seems that an accurate measurement system can be achieved.