Accuracy and reliability of 3D stereophotogrammetry: A comparison to direct anthropometry and 2D photogrammetry

Abstract

Objective: To evaluate the accuracy of three-dimensional (3D) stereophotogrammetry by comparing it with the direct anthropometry and digital photogrammetry methods. The reliability of 3D stereophotogrammetry was also examined.

Materials and methods: Six profile and four frontal parameters were directly measured on the faces of 80 participants. The same measurements were repeated using two-dimensional (2D) photogrammetry and 3D stereophotogrammetry (3dMDflex System, 3dMD, Atlanta, Ga) to obtain images of the subjects. Another observer made the same measurements for images obtained with 3D stereophotogrammetry, and interobserver reproducibility was evaluated for 3D images. Both observers remeasured the 3D images 1 month later, and intraobserver reproducibility was evaluated. Statistical analysis was conducted using the paired samples t-test, intraclass correlation coefficient, and Bland-Altman limits of agreement.

Results: The highest mean difference was 0.30 mm between direct measurement and photogrammetry, 0.21 mm between direct measurement and 3D stereophotogrammetry, and 0.5 mm between photogrammetry and 3D stereophotogrammetry. The lowest agreement value was 0.965 in the Sn-Pro parameter between the photogrammetry and 3D stereophotogrammetry methods. Agreement between the two observers varied from 0.90 (Ch-Ch) to 0.99 (Sn-Me) in linear measurements. For intraobserver agreement, the highest difference between means was 0.33 for observer 1 and 1.42 mm for observer 2.

Conclusions: Measurements obtained using 3D stereophotogrammetry indicate that it may be an accurate and reliable imaging method for use in orthodontics.

Keywords: 3D stereophotogrammetry; Direct anthropometry; Photogrammetry.

Figure 1.

(A) Two-dimensional photogrammetry with millimeter calibration ruler. (B) Direct anthropometry with a digital millimeter sliding caliper.

Figure 2.

Three-dimensional stereophotogrammetric image with anatomic landmarks. Landmark abbreviations: Tr indicates tragus; Ex, exocanthion; En, endocanthion; Gb, glabella; N, nasion; Prn, pronasal; Cl, columella; Al, alare; Sn, subnasal; Ls, labiu m superior; St, stomion; Li, labium inferior; Sm, supramental; Me, menton; Ch, chellion.