Evaluation of two stereophotogrametry software for 3D reconstruction of virtual facial models

ABSTRACT Objective: The present study aimed to evaluate the accuracy of 3D facial soft tissue virtual models produced by two photogrammetry softwares (AgiSoft Photoscan and 3DF Zephyr Free), when compared to those created by cone beam computed tomography (CBCT). Methods: Ten patients were submitted to two sequences of photographs performed with a DSLR camera (with and without the aid of a ring flash) and CBCT scans. Each photo series for each patient was processed with the softwares, and at the end, five models of each patient were generated: 1) CBCT, 2) AAL (Agisoft Ambient Light), 3) AFL (Agisoft Flash Light), 4) ZAL (Zephyr Ambient Light), and 5) ZFL (Zephyr Flash Light). Color coded maps and root-mean-square (RMS) distances were used to compare the photogrammetry models to the CBCT ones. Results: One sample t-test showed significant differences between all methods versus CBCT. The worst results were seen in the ZAL group (discrepancies up to 5.17mm), while the best results were produced by AAL group (discrepancies up to 2.11mm). Conclusions: It can be concluded that this type of virtual facial models are reasonably accurate, although not perfect, and considering its lower biological and financial cost, they may play an important role in specific situations.

摘要
目的：本研究旨在评估两款摄影测量软件（AgiSoft Photoscan与3DF Zephyr Free）生成的三维面部软组织虚拟模型，与锥形束计算机断层扫描（cone beam computed tomography, CBCT）构建的模型的准确性。
方法：招募10名患者，分别使用数码单反相机（Digital Single Lens Reflex, DSLR）拍摄两组照片序列——一组搭配环形闪光灯（ring flash），另一组不使用闪光灯辅助——并对所有患者进行CBCT扫描。针对每位患者的每组照片序列，分别使用两款软件进行处理，最终每位患者可生成5组模型：1）CBCT模型；2）AAL（Agisoft环境光模式，Agisoft Ambient Light）；3）AFL（Agisoft闪光灯模式，Agisoft Flash Light）；4）ZAL（Zephyr环境光模式，Zephyr Ambient Light）；5）ZFL（Zephyr闪光灯模式，Zephyr Flash Light）。本研究采用颜色编码映射图与均方根（root-mean-square, RMS）距离，将摄影测量生成的模型与CBCT模型进行对比分析。
结果：单样本t检验结果显示，所有摄影测量模型与CBCT模型之间均存在显著差异。其中ZAL组的偏差最大，最大偏差可达5.17mm；而AAL组的偏差最小，最大偏差仅为2.11mm。
结论：综上可知，此类虚拟面部模型虽非完美无缺，但具备尚可的精度；且鉴于其较低的生物学与经济成本，可在特定场景中发挥重要作用。