Position detection in a magnetic field

A neurosurgical system providing position detection in a MRI environment, the system comprising:

• a drive and trajectory guide assembly including:
• a base defining an instrument trajectory;
• a first stage coupled to the base along the trajectory;
• and
• a second stage movably coupled to the first stage and operable to move one or more surgical instruments coupled thereto with respect to the base and the first stage;
• and
• a position detection assembly including:
• an encoder coupled to the second stage, the encoder comprising a translucent substrate and one or more light blocking indicia disposed thereon;
• a light source coupled to a first control module adapted to provide one or more electrical signals to the light source;
• at least one input optical fiber coupled to the light source on an input fiber first end and disposed at a point adjacent an encoder first side on an input fiber second end;
• a light detector array coupled to a second control module adapted to receive one or more electrical signals produced by the light detector array;
• at least one output optical fiber disposed at a point adjacent an encoder second side on an output fiber first side and coupled to the light detector on an output fiber second side;
• and
• wherein the input fiber second end and the output fiber first end are stationarily mounted relative to the base and the first stage.

A method of fabricating a position detection assembly operable in a magnetic field, the method comprising:

• forming a first position assembly housing, including forming at least one recess for holding a portion of at least one input optical fiber;
• forming a second position assembly housing, including forming at least one recess for holding a portion of at least one output optical fiber;
• forming an encoder having an encoder first side and an opposite encoder second side, including forming a translucent substrate and one or more light blocking indicia disposed thereon;
• positioning the encoder between the first and the second position assembly housings;
• positioning a light source effectively outside the electromagnetic field;
• optically coupling the light source and a point adjacent the encoder first side using at least one input optical fiber, including coupling an input fiber first end to the light source and inserting a portion of an input fiber second end into the at least one recess of the first position assembly housing;
• positioning a light detector array effectively outside the electromagnetic field;
• and
• optically coupling the light detector array and a point adjacent the encoder second side using at least one output optical fiber, including inserting a portion of an output fiber first end into the at least one recess of the second position assembly housing and coupling an output fiber second end to the light detector array.

A method of detecting a position of a surgical instrument, the method comprising:

• moving an encoder including a translucent substrate and one or more light blocking indicia in concert with the surgical instrument;
• illuminating the encoder using a light source by way of at least one input optical fiber, wherein movement of the one or more light blocking indicia disposed on the translucent substrate interrupts light from passing through the encoder;
• detecting the light passed through the encoder using a light detector array by way of at least one output optical fiber;
• and
• determining one or both of a relative or an absolute position of the surgical instrument.