The computed cranial focal point

IntroductionStereophotogrammetry is a radiation-free method for monitoring skull development after craniosynostosis repair. Lack of clear fixed reference points complicate longitudinal comparison of 3D photographs. Therefore we developed the ‘computed cranial focal point’ (CCFP).MethodsThe CCFP was calculated in segmented 3D CT-scans of 36 adult subjects using Matlab. The robustness of the CCFP calculation was evaluated in predefined hemi-ellipsoid shapes. Finally we used the CCFP in two clinical cases to correlate CT data with 3D-photographic data.ResultsThe CCFP calculation was found to be hardly influenced by incomplete or deformed surface data which resulted in small deviations (<2.5 mm). The average position of the CCFP of the skin relative to the sella turcica was at (0.0, 27.1, 19.4) mm, with CCFPσ (0.6, 4.6, 3.9) mm. The mean difference between the CCFP for the skull and skin was (−0.1, 1.9, −1.4) mm, with CCFPσ (0.5, 1.4, 1.0) mm. Using the CCFP in two cases to correlate the skin from a 3D-photo and the segmented skin from a CT-scan resulted in absolute mean differences of 0.7 and 2.3 mm, with a standard deviation of 1.1 mm in both cases.ConclusionThe CCFP calculation is a robust method to define a reference point relative to the sella turcica based on the skin or cranial bone surfaces. The CCFP can be used to correlate 3D photographs with CT-scan data or for longitudinal radiation-free comparison of 3D-photos.