CAMRT Radiography Practice Exam

What happens to patient dose when the focal spot size is decreased, assuming other factors are unchanged?

1. Increased dose

2. Decreased dose

3. No change to patient dose

4. Variable results depending on technique

The correct answer is: No change to patient dose

When the focal spot size is decreased, the principal effect is on the sharpness and resolution of the image produced during radiographic imaging. However, the actual dose received by the patient remains unchanged if all other factors, such as exposure time, kilovoltage (kV), and milliamperage (mA), are kept constant. The focal spot size primarily influences spatial resolution and the heat capacity of the anode, but it does not directly affect the amount of radiation that is delivered to the patient. A smaller focal spot can improve image detail because it reduces the penumbra effect, thereby enhancing the sharpness of the image, particularly for small structures. Nonetheless, since dose is determined by the factors related to the exposure settings rather than the focal spot size alone, the assumption is that the patient dose remains level when only the focal spot size is altered. This understanding reflects the importance of considering multiple technical factors during radiographic procedures, emphasizing that while the focal spot size is crucial for image quality, it does not intrinsically enhance or reduce patient dose when other variables remain constant.