Which imaging modality uses a dual-energy X-ray beam to determine the areal mass of tissue and estimate bone mineral density?

Which imaging modality uses a dual-energy X-ray beam to determine the areal mass of tissue and estimate bone mineral density?

• A. Quantitative ultrasound
• B. MRI
• C. CT
• D. DXA

Answer: (D)

Dual-energy X-ray absorptiometry works by exposing the body to two X-ray energy levels. Different tissues attenuate these energies differently, so the device separates mineral content from overlying soft tissue and calculates bone mineral density as an areal measurement (grams of mineral per square centimeter). This low-dose, quick test is the standard screening method for osteoporosis, typically at the spine and hip. Other imaging modalities don’t provide this areal BMD in the same way: quantitative ultrasound uses sound waves and doesn’t measure mineral content; MRI relies on magnetic fields and isn’t used to assess bone mineral density; CT can estimate density but yields volumetric BMD and involves higher radiation, making it less ideal for routine screening compared with DXA.

Dual-energy X-ray absorptiometry works by exposing the body to two X-ray energy levels. Different tissues attenuate these energies differently, so the device separates mineral content from overlying soft tissue and calculates bone mineral density as an areal measurement (grams of mineral per square centimeter). This low-dose, quick test is the standard screening method for osteoporosis, typically at the spine and hip. Other imaging modalities don’t provide this areal BMD in the same way: quantitative ultrasound uses sound waves and doesn’t measure mineral content; MRI relies on magnetic fields and isn’t used to assess bone mineral density; CT can estimate density but yields volumetric BMD and involves higher radiation, making it less ideal for routine screening compared with DXA.