American Registry of Radiologic Technologists (ARRT) Practice Exam

When is more high energy photons produced in an X-ray beam?

1. Low kVp

2. High kVp

3. Variable kVp

4. Constant kVp

The correct answer is: High kVp

The production of high-energy photons in an X-ray beam is directly associated with the kilovolt peak (kVp) setting used during the imaging process. When a high kVp is utilized, the potential difference applied across the X-ray tube is greater. This higher potential difference allows the electrons, which are generated in the cathode, to gain more kinetic energy as they travel towards the anode. Upon striking the anode, these high-energy electrons are capable of producing higher-energy photons. These high-energy photons are more penetrating and improve the quality of the X-ray image by enhancing contrast and reducing patient dose while still achieving adequate image density. In contrast, lower kVp settings do not impart enough energy to the electrons, resulting in the production of lower-energy photons, which are less effective at penetrating tissues. Variables such as constant kVp and variable kVp refer to specific operational modes of a radiographic system, but they do not inherently increase the energy of the emitted photons like the overall high kVp setting does.