Measurement Error and Reliability of three available 3D Superimposition Methods in Growing Patients

Abstract

Introduction: Cone-Beam Computed Tomography (CBCT) images can be superimposed, allowing a three-dimensional (3D) evaluation of growth changes and treatment effects. One of the main challenges of 3D superimposition of serial images is to understand that linear/angular measurements in two-dimensional (2D) and 3D images are not directly applicable, due to differences in size, shape and relative spatial location of skeletal, dental and soft tissue between the two imaging systems. Most of the limitations of 3D superimposition techniques are related to imaging and landmark identification errors and software/hardware related errors. Objective: The aims of this research are to determine and compare the intra-rater reliability generated by three 3D cephalometric superimposition methods, and to determine and compare the changes observed in treated cases by the three methods over an average period of approximately 24 months using CBCT images acquired from an iCAT machine. Methods: Thirty-six growing individuals (11-14 years old) were selected from patients that received orthodontic treatment at the University of Alberta. Before and after treatment (on average 24 months apart) CBCTs were analyzed using three superimposition methods (two voxel-based and one landmark-base). The superimposed scans with the two voxel-based methods were then used to construct surface models and quantify differences using the open-source SlicerCMF software, while the distances in the landmark-derived method were calculated manually through a formula using Excel. 3D linear and angular measurements computed with each method were then compared. Results: Repeated measurements with each method separately presented good to excellent intraclass correlation coefficient (ICC). Reproducibility of the quantitative assessments among the three methods had a smaller agreement with a wide range of confidence interval. Conclusions: The findings of the research indicate good to excellent intra-examiner reliability of the three 3D superimposition methods when assessed individually. However, when assessing reliability among the three methods, the ICC demonstrated less powerful agreement with a wide range of confidence interval. ICC values were the lowest when compared the landmark-based method and the voxel-based (CMFreg/Slicer and Dolphin) methods. Moderate to excellent agreement was observed for the intra-examiner reliability when compared the voxel-based methods against each other. The landmark-based method generated the highest measurement error among the three methods.