Geometric plane alignment as a methodological requirement for accurate angular measurement in three-dimensional...

Accurate angular measurements derived from three-dimensional (3D) radiological imaging are essential for morphometric analysis, surgical planning, and implant design. However, measurements performed on standard sagittal, coronal, and transverse sections may not reflect true spatial geometry due to projection-related distortions. This study aimed to develop and validate a reoriented plane protocol to improve the accuracy and reproducibility of angular measurements in 3D imaging.Five anatomically accurate plastic skull models were used to define four craniofacial angles (∠Co-Id-Co, ∠Go-Gn-Go, ∠Co-Go-Gn, ∠N-Rza-Pr), and all measurements were independently performed by three observers. Direct goniometric measurements served as the reference standard. CT scans (0.625 mm slice thickness) were analyzed using standard sectional planes and a reoriented plane approach aligning the measurement plane with the true spatial configuration of landmarks. Intraobserver and interobserver reliability were assessed using intraclass correlation coefficients (ICC), and agreement was evaluated with Bland-Altman analyses.Goniometric measurements showed mean values of 55.8°±4.2°, 72.9°±4.9°, 113.5°±6.5°, and 36.5°±5.7° for the respective angles. Reoriented plane measurements produced nearly identical results with minimal bias (e.g., 0.002° for ∠Co-Go-Gn) and narrow limits of agreement. In contrast, standard sectional measurements demonstrated substantial deviations, with mean biases reaching - 36.47° in coronal sections. The reoriented plane method showed excellent intraobserver and interobserver reliability (ICC up to 0.950, p < 0.001).Aligning the measurement plane with the true landmark-defined plane significantly improves angular measurement accuracy and reproducibility in 3D radiological datasets, offering a robust methodological framework for clinical and research applications.