Final answer:
The fluoroscopic image brightness will become dimmer as the FOV is reduced with tighter collimation due to less radiation reaching the image receptor, akin to the effect seen when increasing magnification on a microscope.
Step-by-step explanation:
When the fluoroscopic field of view (FOV) is reduced with tighter collimation, the image brightness will generally become dimmer. This is due to the reduced amount of radiation reaching the image receptor, as a smaller area of the patient's body is being irradiated and contributing to the image formation. To maintain the brightness of the image, adjustments can be made to the system, such as increasing the X-ray tube current, increasing the time over which the X-rays are gathered, or by manipulating the gain of the image receptor system. The analogy can be made to a microscope where as one increases magnification, the lens aperture decreases, and one must adjust the illumination to compensate for a darkening image. Similarly, in fluoroscopy, as the FOV decreases (akin to increasing magnification), there is less light (or X-ray photons in this case), thus resulting in a darker image unless compensated for by the system's adjustments.