Which technical adjustment would "harden" the x-ray beam?

The process of "hardening" the x-ray beam refers to the increase in the average energy (or quality) of the x-ray photons in the beam. This results in a beam that is more penetrating, allowing it to pass through thicker or denser parts of the body with greater effectiveness.

Adding filtration is the correct method to achieve beam hardening. Filtration involves placing a material, usually aluminum, in the path of the x-ray beam. The filtration process absorbs lower energy photons, which are less likely to penetrate tissues and contribute to patient dose without improving image quality. By removing these lower energy photons, the overall quality of the radiation beam is improved, effectively "hardening" it. This allows for more effective imaging while also minimizing unnecessary radiation exposure to the patient.

In contrast, increasing or decreasing the kilovoltage peak (kVp) influences the overall energy of the beam but doesn't specifically refer to the act of hardening it through filtration. While higher kVp can produce a more penetrating beam, the term "hardening" specifically describes the filtering process that selectively removes less desirable, low-energy photons from the beam.