Three-dimensional A-mode ultrasound calibration and registration for robotic orthopaedic knee surgery

Background: Registration is a key step for computer-navigated robot-assisted surgery. Registration links the live patient anatomical location to the prescanned CT or MRI images, so that predesigned procedures can be performed accurately. Fiducial markers or mechanical probes are usually used to identify anatomical features or collect data points for registration. This conventional invasive approach is common; however, using ultrasound probes may provide a non-invasive alternative. Methods: This report presents investigations of selecting an A-mode ultrasound transducer, calibrating it, analysing the ultrasound signal and using it to register phantom-sawbones of tibia and femur as well as cadaveric specimens. To ensure accurate registration, the A-mode ultrasound probe is calibrated by a designed calibration system. Detailed mathematical derivation and procedures for the calibration are provided in the Appendix. The calibration and registration experiments were performed in conjunction with MAKO Surgical Corporation's Tactile Guidance System™ (TGS™) at their headquarters and at the South Florida Spine Clinic for cadaveric experiments. Results: Calibration results show that an A-mode ultrasound probe can reach the same accuracy level as a mechanical probe. By using the A-mode ultrasound probe, averaged root mean square errors (RMSE) are <0.5 mm for calibration, <1.0 mm for phantom-sawbones and <2.0 mm for cadaveric specimens. Conclusion: The registration results from phantom and cadaveric experiments are suitable for clinical applications. A-mode ultrasound registration is a viable option for registration of the bones in orthopaedic knee surgery but with reduced incision size.