Tracked Bipolar Stimulator Greg Wempe Advised by: Dr. Robert L. Galloway, Ph.D. Mr. Steven L. Hartmann Final Presentation March 23, 2001

Project Background Mapping of points on/in the brain is necessary in most surgical cases Current pre-operative methodology limited Stereotactic frames (top) Current real-time methodology limited Articulated arm (top/bottom) “Post-It” notes Three-dimensional tracking techniques are currently available and readily applicable

Tracking Stimulator Position and Spatial Orientation 24 infrared light emitting diodes (IREDs) which fire in time sequence spiral around the handle of the probe. The sensor unit, the Optotrak, returns the position for each IRED that it can “see” every 300 microseconds. The probe can be calibrated by creating a reference file, known as a rigid body file, containing the locations of each of the IREDs and the endpoint of the probe in a reference coordinate system.

Tracking Stimulator Position and Spatial Orientation The location of the probe tip is then passed through a transformation matrix that calculates its position in sensor space. The probe’s position is lastly mapped into the space defined by a small, stationary reference emitter with six IREDs. This allows the position of the sensor unit to drop out of the equations, and one gains the ability to move this large, cumbersome device without worry during use.

Target Problems Inaccuracies in calibration caused by the lack of rigidity in stimulator leads Inaccuracies in calibration caused by offset characteristic of stimulator carriage Inaccuracies in calibration caused by inability to properly rotate bipolar system about a single point

Project Definition Design a sheath and carriage system that will integrate into the present software package and allow for the tracking and marking of desired points. Additional software coding may be required for proper incorporation.

Initial probe handle and carriage with ablator attachment. Current Status New registration software integrated. Stimulator lead sheath is complete. Rigid-body files (calibration) have been compiled. Initial probe handle and carriage with ablator attachment. Stimulator carriage connection to IRED probe is being machined. Roll black-out isolated and eliminated. Power source connectors must be converted for use on updated source.

Calibration Improvement The probe’s dimensions were measured and used to design a sheath made from Delran. The sheath was flared to insure a secure fit against the stimulator lead cap and narrowed to provide necessary line-of-sight. The carriage will be cast from aluminum or steel.

Calibration Improvements OPTOTRAK system provides 0.3mm accuracy to marker. Iterative rigid-body calibration process insures 3D RMS error of 0.5mm. Average largest single-marker error without sheath: 1.497 ± 0.695mm. Average largest single-marker error with sheath: 0.967 ± 0.577mm.

The Optotrak 3220 Localizing Planes Key Questions Device linearity and effects on roll Blackout orientation Testing processes Accuracy determination The Optotrak 3220 Localizing Planes

Future Plans Possible incorporation of labeling algorithm into registration TREFRE analysis for sheath accuracy. Rotation piece for use with 3mm ball.

Future Plans