Patent ID: 7603161

Claim:
An assembly for detecting a position of a surgical instrument in a magnetic field, the assembly comprising: an encoder having an encoder first side and an oppositely positioned encoder second side, the encoder including a translucent substrate and one or more light blocking indicia disposed thereon, the one or more light blocking indicia including an array of absolute position indicia; a light source; at least one input optical fiber extending from an input fiber first end to an input fiber second end, the input fiber first end coupled to the light source and the input fiber second end disposed at a point adjacent the encoder first side; a light detector array; at least one output optical fiber extending from an output fiber first end to an output fiber second end, the output fiber first end disposed at a point adjacent the encoder second side and the output fiber second end coupled to the light detector array; and wherein the light detector array detects an absolute position of a depth of the surgical instrument relative to an anatomy using the absolute position indicia and the encoder is stationarily mounted to the surgical instrument.