骨质疏松症在我国造成70-80%的中老年骨折，是重要的公共卫生问题之一。双能X线吸收测定法（DXA）测得的骨矿物质密度（BMD）已广泛应用于骨质疏松的临床评估。但DXA测得的是二维BMD，受骨结构大小及周围组织的影响。定量CT可获得更精准的三维BMD，但X线辐射剂量显著增加。MRI没有辐射风险，最近发展起来的量化磁敏感成像（QSM）技术可定量获得组织的磁敏感系数。骨的磁敏感系数从理论上可反映骨中抗磁性羟基磷灰石钙的含量，且本项目预实验结果已表明腰椎QSM值随BMD值的降低而升高。本项目拟开展腰椎QSM新方法及其对骨质疏松症评估价值的研究，希望通过腰椎QSM的序列设计与优化、图像重建、相位解缠绕、QSM重建、参数联合估计等方面的深入研究，为临床提供快速精准可靠的腰椎QSM新方法，并评估腰椎QSM在骨质疏松高发人群的诊断价值。本项目研究有望为骨质疏松症评估提供新的影像学生物标记。

Osteoporosis causes approximately 70-80% of bone fractures in old people in China, and it is one of the most important public health problems. Bone mineral density (BMD) measured by dual energy X-ray absorptiometry (DXA) is widely used for assessing osteoporosis in routine clinical practice. However, the two-dimensional DXA measurement of BMD is complicated by bone size and surrounding tissues. This problem is overcome by volumetric BMD measurement using quantitative computed tomography (QCT). Compared with DXA, QCT enables the purely trabecular BMD measurement that is more sensitive to disease and therapy-related changes, and it provides an improved discrimination of vertebral and nonvertebral fractures, but with significantly increased irradiation.. Quantitative susceptibility mapping (QSM) is a non-ionizing radiation MRI technique that can quantify the magnetic susceptibility of biological tissues. The magnetization coefficient of bone theoretically reflects the content of diamagnetic calcium hydroxylapatite in bone, and our preliminary results demonstrate that the QSM value of lumbar spine decreases with its BMD value. This project aims to further develop novel lumbar spine QSM methods and investigate their applications to the assessment of osteoporosis. This project will provide fast, accurate and reliable solutions for the lumbar spine QSM by developing novel methods in pulse sequence design and optimization, image reconstruction, phase unwrapping, field-to-source inversion, and collaborative parameter estimation. Moreover, this project will evaluate the performance of lumbar spine QSM on assessing osteoporosis in the corresponding high risk population. In all, this project is expected to provide a new imaging biomarker for the evaluation of osteoporosis.