How is bone density measured?

Bone mineral density (BMD) can be measured using three primary methods.

1. Ultrasound: Ultrasound-based BMD assessment measures bone mineral content and bone strength by evaluating the speed of sound (SOS) and attenuation of ultrasound waves. This technique is sensitive to soft tissue, bone tissue, and bone marrow structures, and the calcaneus (heel bone) is the most commonly examined site. Currently, ultrasound is primarily used for screening individuals at risk for osteoporosis and for assessing the risk of osteoporotic fractures.

2. Computed Tomography (CT): CT typically measures trabecular BMD in the lumbar spine and proximal femur. Quantitative CT (QCT) is a clinically validated method for measuring BMD in the spine, hip, forearm, and whole body. QCT is mainly employed to evaluate disease severity associated with abnormal BMD and to monitor treatment response. Importantly, QCT provides more accurate measurements in patients with obesity or low body mass index (BMI).

3. Dual-Energy X-ray Absorptiometry (DXA): DXA quantitatively assesses bone mineral content. This technique enables precise measurement of bone mass at any skeletal site, with high accuracy and minimal radiation exposure to the patient. DXA uses an X-ray tube equipped with a special filter to generate two distinct photon energy beams—low-energy and high-energy. After passing through the body, these beams are detected by the scanner system, and the acquired data are processed by a computer to calculate bone mineral content.