Why do normal air-filled lungs appear black (radiolucent) on a chest X-ray radiograph?
Answer and explanation
Correct answer: A. Low physical density of air with minimal X-ray photon attenuation
- Step 1: X-ray attenuation depends directly on physical density and path length. Step 2. Air has an extremely low density (~0.0012 g/cm3), allowing almost all incident X-ray photons to pass through unattenuated to blacken the radiographic detector. Answer: Air has very low physical density and absorbs minimal X-ray photons, exposing the detector. Why not the others: Complete absorption would make lungs white; air does not emit visible light; oxygen does not backscatter X-rays.
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