Bone mineral density (BMD), referred to as bone mineral density, is currently the best quantitative indicator for diagnosing osteoporosis, predicting the risk of osteoporotic fractures, monitoring the natural course of disease, and evaluating the efficacy of pharmacological interventions. BMD reflects only about 70% of bone strength. The risk of fracture is associated with low BMD, and the risk of fracture is increased by the presence of other risk factors. Bone density measurement methods: Dual-energy X-ray absorptiometry (DXA) is currently the internationally accepted method of bone density examination, and its measured value is used as the gold standard for the diagnosis of osteoporosis. Other bone density examination methods such as various single photon (SPA), single energy X-ray (SXA), quantitative computed tomography (QCT,) etc. can also be used for reference in the diagnosis of osteoporosis according to specific conditions.