The ratio of the output to the input in an image intensifier tube is called:

The concept of brightness gain refers to the ratio of the output brightness to the input brightness in an image intensifier tube. This ratio is crucial in understanding how effectively the image intensifier enhances the brightness of the incoming X-ray image to produce a clearer, more visible output image for observation and analysis.

In the context of fluoroscopy, brightness gain is particularly important because it determines how well the system can amplify the signal it receives from the X-ray source. The higher the brightness gain, the more effective the image intensifier is at producing a bright, well-defined image while minimizing the amount of radiation exposure required to achieve that image.

Brightness gain is a combination of two components: flux gain and minification gain. Flux gain refers to the increase in the number of photons that exit the image intensifier compared to those that enter, while minification gain relates to the reduction in the physical size of the image cast by the input screen to the output screen, thereby concentrating those photons into a smaller area and increasing brightness.

Other terms listed, although related to imaging, are not synonymous with the defined concept of brightness gain. Image quality pertains to the clarity and resolution of the imaging result but does not specifically quantify the input-to-output brightness relationship. Quantum efficiency refers to how