Passive markers for ultrasound tracking of surgical instruments.

A family of passive markers is presented by which the position and orientation of a surgical instrument can be computed from its ultrasound image using simple image processing. These markers address the problem of imaging instruments and tissue simultaneously in ultrasound-guided interventions. Marker-based estimates of instrument location can be used in augmented reality displays or for image-based servoing. Marker design, measurement techniques and error analysis are presented. Experimentally determined in-vitro measurement errors of 0.22 mm in position and 0.089 rad in orientation were obtained using a standard ultrasound imaging system.