Standardization of 3-D CT Measurements for Length and Angles by Matrix Transformation in the 3-D Coordinate System

Abstract

Objective

We attempted to establish a new 3-D cephalometry with helical computed tomography (CT) by introducing the matrix transformation of the 3D coordinate system.

Subjects and Methods

Three-dimensional cephalometric landmarks on the craniofacial bones were expressed as 3-D vectors originating from the center of the sella. These vectors were standardized by the matrix transformation so that the midsagittal plane and cranial base line coincided with the XZ plane and X axis of the 3-D coordinate system, respectively. We also applied this new method to trace the normal growth of the craniofacial bones in 44 patients with head and neck cancer (age range, 5 to 26 years; 19 women and 25 men).

Results

The accuracy for length measurements was less than 3% of standard error of means with a slice thickness of 1 or 3 mm for 28 out of the 29 length measurements recorded. The precision errors by repeated measurements were 0.8% to 1.0% coefficients of variation for intra- and interobserver variability. Standardization of 3-D vectors representing the cephalometric landmarks allowed us to assess successfully the age-related transition of these landmarks of the patients' craniofacial bones.

Conclusion

A new assessment method for 3-D CT cephalometry has been developed by standardizing cephalometric landmarks using a matrix transformation of the 3-D coordinate system. This new assessment method may offer potential in planning plastic and reconstructive surgery.