Improving target registration error in vertebra during image-guided spine surgery

22 August 2017

Purpose: To evaluate different factors affecting target registration error (TRE) in pedicle screw placement during image-guided spine surgery(IGSS).
Materials and methods: Computed tomography (CT)-compatible markers are placed over anatomical landmarks that are feasible and routinely used in surgical procedures. TRE is obtained directly for the marker that is placed on a pedicle of one vertebra. First, optimum selections of landmarks are proposed for different landmarks according to the minimum achievable TRE values in different configurations. These anatomical landmarks are feasible and accessible to overcome constraints that may be imposed during surgical procedures. Second, the effect of fiducial weighting on corresponding points to overcome anisotropic localization error based on maximum likelihood approach is evaluated. Third, an experimental model for FLE is derived to obtain the weights. At the end an error zone was obtained for each marker to indicate the possible acceptable deviation from the marker’s exact location in practice. This study was performed on a spine phantom.
Results: Results showed that selecting an optimum configuration of landmarks led to an improvement of 30% in the accuracy of TRE. In addition, optimum weighting of optimally chosen fiducials in the FLE model to incorporate anisotropic localization error in the registration algorithm, led to an improvement of 28% in theTRE.
Conclusion: Landmark configuration, transformation parameters, and fiducial localization error are the factors that considerably affect the total TRE value. To obtain the minimum reachable TRE value, these issues should be considered in TRE derivations. This optimum configuration of landmarks and the anisotropic weighing of fiducials have significant impact on the registration accuracy that is great concern for surgeons during IGSS.