How many different x-ray photon energies pass through the patient in DXA?

• A. One
• B. Two
• C. Three
• D. Four

Answer: (B)

DXA uses dual-energy radiography. The beam that passes through the patient consists of two distinct photon energy components. Measuring attenuation at both energies lets the system separate the effects of bone from soft tissue, because bone and soft tissue absorb these energies differently. Having two independent measurements provides enough information to solve for bone mineral content and density, something you can’t do with a single energy. In practice, the two energies are produced by using different kVp settings or filtration, creating a low-energy and a high-energy component. So, two energies pass through the patient.