Which of the following will INCREASE attenuation of x-rays inside the body?

• A. increasing SID and correcting the mAs
• B. decreasing kVp and correcting the mAs
• C. using more added filtration
• D. increasing kVp and correcting the mAs

Answer: (B)

Attenuation in tissue rises when the beam energy is lower because low-energy photons are more likely to interact with atoms in the body, especially by photoelectric absorption, which removes photons from the beam as they pass through. Lowering the kilovoltage peak shifts the beam toward these lower energies, so more photons are absorbed or scattered before exiting the patient. Even if you adjust the mAs to maintain the same image receptor exposure, the physics of attenuation doesn’t change—the photons are still lower in energy and more of them get attenuated. Increasing the kVp raises photon energy and reduces attenuation, while adding filtration removes the low-energy portion of the spectrum, also decreasing attenuation. Increasing SID mainly alters geometric factors and dose to the image receptor rather than the intrinsic attenuation within the body.