What is the basic mechanism of tissue damage from X-ray exposure?

• A. Ionization of molecules in living tissues
• B. Thermal heating only
• C. Mechanical tearing of tissues
• D. Increase in tissue elasticity

Answer: (A)

Ionization of molecules in living tissues is the fundamental way X-ray exposure causes damage. When X-ray photons interact with cells, they have enough energy to knock electrons off atoms, creating ions. This ionization is not just a single event; it triggers chemical changes, especially through the radiolysis of water, which produces reactive free radicals such as hydroxyl radicals. These radicals, along with other reactive species, go on to damage critical biomolecules like DNA, proteins, and membranes. DNA damage can be direct, from the photon ionizing the DNA itself, or indirect, via these free radicals that cause breaks and mutations. The cell’s repair mechanisms can fix many lesions, but some damage persists and may lead to cell death, mutations, or long-term risks such as cancer. Thermal heating is negligible at diagnostic X-ray doses, and mechanical tearing or increased tissue elasticity are not how X-rays produce tissue injury.