X线头影测量术对临床治疗具有重要指导作用。传统头颅定位片和CBCT都利用X线成像。在影像技术推动和临床需求拉动的双重作用下，三维头影测量研究迫在眉睫。目前基于CBCT的三维头影测量存在电离辐射、软组织信息缺乏、定义颅颌面正中矢状平面存在争议等缺陷。本项目提出基于人类头部结构一体化与模块化特点的MRI-only三维头影测量设想，以正常对照组与颅颌面畸形患者为样本，通过比较MRI合成CT和真CT，完成MRI合成CT的生成与优化，满足三维头影测量的精确性要求；借鉴神经科学中的4种MRI脑中线定位方法，筛选脑中线正中矢状平面，并依据模块化界限，构建头部结构的MRI-only三维参考坐标系；利用MRI-only流程中软硬组织显示的双重优势，参照Gateno-Xia原则，建立颅颌面软硬组织的MRI-only三维头影测量分析系统。为脑-颅-颌-面生长发育、畸形发生、精准治疗等研究提供全新方法和科学视角。

X-ray cephalometry plays an important role in clinical treatment. Traditional cephalogram and CBCT are all X-ray imaging . Under the dual action of image technology and clinical demand, the research of three-dimensional cephalometry is urgent. At present, three-dimensional cephalometry based on CBCT has some defects, such as ionizing radiation, lack of soft tissue information, controversy in defining cranio-maxillofacial median sagittal plane and so on. In this project, MRI-only three-dimensional cephalometry based on integrated and modular organization of human head was put forward. With normal control group and patients with cranio-maxillofacial deformities were taken as samples, by comparing MRI synthetic CT and true CT, generation and optimization of MRI synthetic CT were performed to meet the accuracy requirements of three-dimensional cephalometry; Learning from the four methods of locating midline of brain in neuroscience, Selecting the most appropriate midline of brain as the median sagittal plane, and According to the modular boundary of human head, the MRI-only three-dimensional reference coordinate system of three-dimensional cephalometry was constructed. According to the principles of Gateno-Xia, a MRI-only three-dimensional cephalometric system for cranio-maxillofacial soft and hard tissue analysis was established by taking the dual advantages of soft and hard tissue display in MRI-only workflow. It provides a new method and scientific perspective for the study of brain-skull-jaw-face growth and development, deformity occurrence, precision treatment and so on.