Development of a technique for recording and transferring natural head position in 3 dimensions.

The purpose of this study was to develop and test a new technique for recording natural head position (NHP) in 3 dimensions and transferring it into a three-dimensional computed tomography (CT) model. In this technique, a digital gyroscope was first attached to a human head using a bite-jig and a face-bow with a set of built-in fiducial markers. The relationship between the gyroscope and fiducial markers was predetermined and kept constant. The orientation (pitch, roll, and yaw) of the head was then recorded by this gyroscope. In next step, the head was CT scanned with the bite-jig and the face-bow in place, and three-dimensional CT models of the head and fiducial markers were generated. The head model was coupled with a predetermined three-dimensional model of the gyroscope assembly via fiducial markers. The three-dimensional head model was reoriented to the recorded orientation by applying the recorded pitch, roll, and yaw to the gyroscope model. Finally, the accuracy of the technique was tested on a human dry skull. The results showed that the NHP was successfully recorded and transferred to the three-dimensional CT model. The orientations between the dry skull and its three-dimensional computer model were absolutely correlated. The difference (the lack of agreement) was within a range of -1.1 to 1.1 degrees, indicating no clinical significance. The authors concluded that our technique could accurately and repeatedly record NHP three-dimensionally and transfer it to a three-dimensional CT head model.