What is a requirement for Single Photon Absorptiometry (SPA) to be valid?

• A. Uniform thickness
• B. Presence of metal plates
• C. Use of contrast media
• D. Measurements taken in air

Answer: (A)

For Single Photon Absorptiometry (SPA) to provide accurate and valid measurements, achieving uniform thickness of the area being measured is essential. This requirement ensures that the absorption patterns of photons are consistent across the region of interest, allowing for precise calculations of bone mineral density. Any variations in thickness could lead to inaccuracies as denser or less dense areas would absorb different amounts of photons, skewing the results.

Other options like the presence of metal plates, the use of contrast media, or measurements taken in air do not affect the validity of SPA. These elements do not contribute positively to the accurate assessment of bone density; in fact, they could potentially complicate the interpretation of the results. Ensuring a uniform thickness is the most crucial factor for maintaining the integrity of the measurement in SPA.