Practical Method to Superimpose Sella Turcica in Serial CBCT Images

Objectives: Skeletal tissue CBCT images should be routinely and reliably used to superimpose discrete images; especially, at the cranial base. However, locating 3D landmarks on curved structures has been complex. In this study, a reproducible method of CBCT superimposition is adapted and improved by employing Amira XImage^® software. Our objective was to develop a practical method for cranial base superimpositions at sella turcica in serial CBCT images. Specifically, to confirm the stability of anterior curvature of hypophyseal fossa during growth. Additionally, comparisons of surface changes in the superimposed images in different regions were made.
Methods: Sample of pre- and post- orthodontic CBCT data were procured from Case Western Reserve University. Cranial base changes in 10 adolescent patients of Class I and II hypodivergent, normodivergent, and hyperdivergent malocclusions, were observed over an average interval of 2 years and 5 months. Cranial base models were superimposed using a rigid registration technique, and 3D models constructed from semi-automatic segmentation in the Amira software. Surface distance changes of the entire cranial base were compared to that of the anterior portion of sella.
Results: Mean surface distance changes were 0.77-1.57± 0.59-1.30 mm and 0.37-0.63 ± 0.29-0.43 mm for the entire cranial base and anterior sella, respectively. The area above a threshold of 0.5 mm was 61.02-74.11% (cranial base) and 38.71-50.94% (anterior sella) as well. Paired t-tests were applied to compare differences between the mean distance and area above the threshold for data of cranial base versus anterior sella. Both illustrated p-values less than 0.0001 and were statistically significant.
Conclusions: A practical method of superimposition of serial CBCT images was developed. Through production of color maps, the surface distance of the anterior portion of sella was shown to change much less than the clivus and remaining cranial base in pre- and post-treatment scans of growing children.