Torsional deformation of an endoscope probe

A recent US patent due to Shan describes a method for identifying the locat ion of the colonoscope in the body during endoscopy. The method depends upo n the integration of measurements recorded by a flexible probe inserted in the biopsy channel at the end of a flexible rod. In this paper, classical results for the elastic rod are used to determine the equations required for this integration process. Particular attention i s paid to the effect of initial curvature or non-axisymmetry of the rod. It is shown that these effects cause predictive errors that increase quadrati cally with the angle subtended by the space curve of the channel, and quite stringent limits must be placed on straightness and symmetry if these erro rs are not to be significant.