A method of minimizing contamination of optical components of a laser resonator is disclosed. One aspect is a drill bit which includes a bit body, and a plurality of roller cones attached to the bit body and able to rotate with respect to the bit body. A signal processor is located within the processor housing for developing an implant data signal. In step S4, a parameter determining unit selects an initial value parameter used in an image search unit from an initial value table on the basis of the input keyword.