How does increasing beam size affect the brightness of fluoroscopic images?

Increasing the beam size in fluoroscopy affects the image brightness due to the physics of X-ray scattering and beam dispersion. When the beam size is expanded, the same amount of X-ray exposure is distributed over a larger area, leading to a dilution of the intensity per unit area. This results in a reduction of the overall brightness of the image.

While the total energy being emitted may remain constant, the effect of spreading that energy over a larger surface area diminishes the concentration of photons that reach the image receptor at any given point, making the image appear dimmer. Thus, the perception of brightness does not increase with a larger beam size; rather, it leads to a decrease in effective image quality because of the less focused delivery of radiation to the receptor.

This contextual understanding clarifies why an increase in beam size does not enhance brightness and impacts the clarity and quality of fluoroscopic images.