A New Method of Real-Time Endoscopic Measurement with an Electric Catheter

A new method for measuring distances using electrically charged jets of water is described, and its precision examined. When combined with endoscopy, this method can be utilized to measured the lengths and areas of objects inside human body cavities. The apparatus used consists of a catheter with three metal needles at the tip, a personal computer, and a commercially available videoendoscopy system. To test the system, a regulated voltage was passed between the catheter tip and a wooden board, and two salt solutions of different concentrations were ejected at three different angles from the catheter to the board. The coordinates of the board were then computed from the amperages of the currents passing through the three jets of saline, and optical distortion was corrected using the computer. The length and area of an object could be measured rapidly by setting electrically the coordinates to match the endoscopic image. Lengths ranging from 10 to 50 mm were measured while varying the distance between catheter tip and board (10, 20, and 30 mm), as well as the angle formed by the catheter and the board (45, 60, and 90 degrees). The mean measurement error was less than 5.6% and accuracy was relatively independent of the angle between catheter and target.