How is bone density measured?

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

1. Ultrasound examination: Ultrasound-based BMD measurement assesses bone mineral content and bone strength by evaluating the speed of sound (SOS) and broadband ultrasound attenuation (BUA). This technique is sensitive to soft tissue, cortical and trabecular bone, and bone marrow structures, and is typically performed at the calcaneus (heel bone). Currently, it is primarily used for screening individuals at risk for osteoporosis and for assessing the risk of osteoporotic fractures.

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

3. Dual-energy X-ray absorptiometry (DXA): DXA measures and evaluates skeletal mineral content. This technique can quantify bone mass at any skeletal site with high precision and minimal radiation exposure. It employs an X-ray tube coupled with specialized filtration to generate two distinct photon energy beams—low-energy and high-energy. After penetrating the body, these beams are detected by the scanner system, and the acquired data are processed by a computer to calculate bone mineral content.