Bone density examination is an important indicator for diagnosing osteoporosis and bone loss. The examination methods include the following: 1, ultrasonography: ultrasound of the heel and forearm, with relatively low accuracy; 2, CT examination: quantitative bone density detection can be performed, with relatively large radiation, which is not widely used clinically; 3, dual-energy X-ray: the gold standard for bone density detection, with short examination time and low radiation dose, which is about 1/20 of the dose of chest X-ray, and can measure bone density of the lumbar spine and hip at the same time.