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 attenuation of ultrasound waves through bone tissue. This technique is sensitive to soft tissues, cortical and trabecular bone, and bone marrow, 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) examination: CT-based BMD measurement typically targets 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. Importantly, 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 that generates two distinct photon energy spectra—low- and high-energy beams—via specialized filtration. After penetrating the body, these beams are detected by a scanning system, and the acquired data are processed by a computer to calculate bone mineral content.