Table 1.

Definition of measurements.

Name	Significance	Method of Calculation
Fiducial Registration error	Registration accuracy Assessment obtained in every case	The Fiducial registration error is the root-mean square of the distance between the localized position of each fiducial as transformed from image space to physical space and the position of that corresponding fiducial localized in physical space.
Target Registration error	Misrepresentation of the tracked device location by the navigation system as opposed to actual position on imaging	The tracked device is placed at a target and its location (x, y, z) is recorded immediately prior to obtaining a verification CT-scan. The navigation CT scan is co-registered to the verification scan and the recorded location of the tracked device is transformed into the verification scan space. The distance between the position of the tracked device now depicted on the verification scan and the actual image of the tracked device provides the target registration error.
Deployment error	Overall accuracy of system	Sum of all errors including fiducial registration error, target registration error, operator error and graft properties