Department of Imaging and Pathology, Division of Medical Physics & Quality Assessment, KU Leuven, Leuven, Belgium.
Department of Imaging and Pathology, Division of Nuclear Medicine & Molecular Imaging, KU Leuven, Leuven, Belgium.
Med Phys. 2023 Nov;50(11):6714-6736. doi: 10.1002/mp.16661. Epub 2023 Aug 21.
Optimization of dental cone beam computed tomography (CBCT) imaging is still in a preliminary stage and should be addressed using task-based methods. Dedicated models containing relevant clinical tasks for image quality studies have yet to be developed.
To present a methodology to develop and validate a virtual adult anthropomorphic voxel phantom for use in task-based image quality optimization studies in dental CBCT imaging research, focusing on root fracture (RF) detection tasks in the presence of metal artefacts.
The phantom was developed from a CBCT scan with an isotropic voxel size of 0.2 mm, from which the main dental structures, mandible and maxilla were segmented. The missing large anatomical structures, including the spine, skull and remaining soft tissues, were segmented from a lower resolution full skull scan. Anatomical abnormalities were absent in the areas of interest. Fine detailed dental structures, that could not be segmented due to the limited resolution and noise in the clinical data, were modelled using a-priori anatomical knowledge. Model resolution of the teeth was therefore increased to 0.05 mm. Models of RFs as well as dental restorations to create the artefacts, were developed, and could be inserted in the phantom in any desired configuration. Simulated CBCT images of the models were generated using a newly developed multi-resolution simulation framework that incorporated the geometry, beam quality, noise and spatial resolution characteristics of a real dental CBCT scanner. Ray-tracing and Monte Carlo techniques were used to create the projection images, which were reconstructed using the classical FDK algorithm. Validation of the models was assessed by measurements of different tooth lengths, the pulp volume and the mandible, and comparison with reference values. Additionally, the simulated images were used in a reader study in which two oral radiologists had to score the realism level of the model's normal anatomy, as well as the modelled RFs and restorations.
A model of an adult head, as well as models of RFs and different types of dental restorations were created. Anatomical measurements were consistent with ranges reported in literature. For the tooth length measurements, the deviations from the mean reference values were less than 20%. In 77% of all the measurements, the deviations were within 10.1%. The pulp volumes, and mandible measurements were within one standard deviation of the reference values. Regarding the normal anatomy, both readers considered the realism level of the dental structures to be good. Background structures received a lower realism score due to the lack of detailed enough trabecular bone structure, which was expected but not the focus of this study. All modelled RFs were scored at least adequate by at least one of the readers, both in appearance and position. The realism level of the modelled restorations was considered to be good.
A methodology was proposed to develop and validate an anthropomorphic voxel phantom for image quality optimization studies in dental CBCT imaging, with a main focus on RF detection tasks. The methodology can be extended further to create more models representative of the clinical population.
牙科锥形束计算机断层扫描（CBCT）成像的优化仍处于初步阶段，应使用基于任务的方法来解决。尚未开发出包含相关临床任务的专用模型来进行图像质量研究。
提出一种方法，用于开发和验证用于牙科 CBCT 成像研究中基于任务的图像质量优化研究的虚拟成人人体体素体模，重点是在存在金属伪影的情况下检测根折（RF）。
该体模是从具有 0.2 毫米各向同性体素大小的 CBCT 扫描中开发的，从中分割出主要的牙齿结构、下颌骨和上颌骨。从较低分辨率的全颅骨扫描中分割出缺失的大解剖结构，包括脊柱、颅骨和剩余的软组织。感兴趣区域没有解剖异常。由于临床数据的分辨率和噪声有限，无法分割精细的牙齿结构，使用先验解剖知识对其进行建模。因此，牙齿的模型分辨率提高到 0.05 毫米。RF 模型以及用于产生伪影的牙修复体模型均已开发完成，并可根据需要插入体模中。使用新开发的多分辨率模拟框架生成模型的模拟 CBCT 图像，该框架结合了真实牙科 CBCT 扫描仪的几何形状、射线质量、噪声和空间分辨率特性。使用射线追踪和蒙特卡罗技术创建投影图像，然后使用经典的 FDK 算法对其进行重建。通过测量不同牙齿长度、牙髓体积和下颌骨，并与参考值进行比较，评估模型的验证。此外，在读者研究中使用了模拟图像，其中两名口腔放射科医生必须对模型正常解剖结构以及建模的 RF 和修复体的逼真度水平进行评分。
创建了一个成人头部模型以及 RF 和不同类型牙修复体模型。解剖学测量值与文献中报告的范围一致。对于牙齿长度测量，与平均值的偏差小于 20%。在所有测量值中，77%的偏差在 10.1%以内。牙髓体积和下颌骨测量值在参考值的一个标准差内。关于正常解剖结构，两位读者都认为牙齿结构的逼真度水平良好。由于缺乏足够详细的小梁骨结构，背景结构的逼真度得分较低，但这是预期的，并非本研究的重点。至少有一位读者认为所有建模的 RF 在外观和位置上都至少足够好，两位读者都认为建模修复体的逼真度水平良好。
提出了一种用于牙科 CBCT 成像中图像质量优化研究的人体体素体模开发和验证的方法，主要侧重于 RF 检测任务。该方法可以进一步扩展，以创建更能代表临床人群的模型。
