Development of an accuracy assessment phantom for surgical navigators

An improved method for assessing the technical accuracy of optical tracking systems for orthopaedic surgical navigation

BACKGROUND

Optical tracking systems (OTSs) are essential components of many modern computer assisted orthopaedic surgery (CAOS) systems but patient movement is often neglected in the evaluation of the accuracy. The aim of this study was to develop a representative test to assess the accuracy of OTSs including patient movement and demonstrate the effect of pointer design and OTS choice.

METHOD

A mobile phantom with dynamic reference base (DRB) attached was designed and constructed. The point registration trueness and precision were evaluated for measurements with both a static and moving phantom.

RESULTS

The trueness of the total target registration error (TTRE) was 1.4 to 2.7 times worse with a moving phantom compared to a static phantom.

CONCLUSION

The accuracy of OTSs for CAOS applications should be evaluated by measurements with a moving phantom as the evaluation of the TTRE with a static frame significantly underestimates the measurement error.

Technical accuracy of an O-arm registered surgical navigator

The objective of this study was to assess the accuracy of a commercial surgical navigator using optical tracking modality with automated registration between O-arm images and the scanned object. Automated registration was enabled by using the spine navigation software of the navigator. The used phantom was designed by the authors of this paper. The surgical navigators and the O-arm are routinely used at Oulu University Hospital, Oulu, Finland. The distances measured with the surgical navigator from the fixed origin of the phantom were compared to the known phantom accuracy assessment coordinates. The error of the surgical navigator was the difference between measured and true values. The mean displacement error was 0.20 mm with a standard deviation of 0.14 mm. The results show that automated registration is very reliable for image guided surgery (IGS) and that the present accuracy assessment method can be used to periodically check surgical navigator accuracy using O-arm data.