American Registry of Radiologic Technologists (ARRT) Practice Exam

What are the primary controls for the number of x-rays produced at the anode?

1. kVp and SID

2. mAs and kVp

3. SID and focal spot size

4. Colimation and mAs

The correct answer is: mAs and kVp

The primary controls for the number of x-rays produced at the anode are mAs and kVp. mAs, which stands for milliampere-seconds, directly influences the quantity of x-rays generated. It determines the amount of electrical current that flows through the x-ray tube, affecting the number of electrons produced at the cathode. A higher mAs results in a greater number of x-rays being produced, which leads to an increased exposure to the patient or film. kVp, or kilovoltage peak, plays a crucial role as well. It affects the energy of the x-rays produced and their penetrating ability. While kVp primarily influences the quality and energy of the x-rays, it also indirectly impacts the quantity produced at the anode. A higher kVp can increase the range of energies of the x-rays, allowing more of them to penetrate the tissue being imaged, and may enhance the overall x-ray yield. The combination of these two factors—mAs for quantity and kVp for both quality and some quantity control—highlights their significance in determining the number of x-rays produced. In contrast, other options include controls that do not primarily influence the quantity of x-rays. For instance, focal spot size and SID (