How does increased kilovoltage peak (kVp) affect differential attenuation of the x-ray beam?

How does increased kilovoltage peak (kVp) affect differential attenuation of the x-ray beam?

• A. Decreased differential attenuation
• B. Increased differential attenuation
• C. No change
• D. Variable depending on tissue

Answer: (A)

Raising kVp raises the energy of the X-ray photons, so the beam becomes more penetrating. Attenuation in tissue mainly happens through two processes: photoelectric absorption, which is very sensitive to photon energy and varies a lot with tissue composition (especially Z) at lower energies, and Compton scattering, which is less sensitive to tissue type and more tied to electron density. When the beam energy is higher, photoelectric absorption becomes less dominant and Compton scattering takes over, making the attenuation of different tissues more similar to each other. As a result, the differences in how much the beam is attenuated by, say, soft tissue versus bone shrink, reducing the differential attenuation. This is why increasing kVp reduces image contrast between tissues, even though it increases overall beam penetration.

Raising kVp raises the energy of the X-ray photons, so the beam becomes more penetrating. Attenuation in tissue mainly happens through two processes: photoelectric absorption, which is very sensitive to photon energy and varies a lot with tissue composition (especially Z) at lower energies, and Compton scattering, which is less sensitive to tissue type and more tied to electron density. When the beam energy is higher, photoelectric absorption becomes less dominant and Compton scattering takes over, making the attenuation of different tissues more similar to each other. As a result, the differences in how much the beam is attenuated by, say, soft tissue versus bone shrink, reducing the differential attenuation. This is why increasing kVp reduces image contrast between tissues, even though it increases overall beam penetration.