Final answer:
In magnification mode of an image intensifier, the patient dose increases due to the need for increased radiation, but the resolution does not inherently improve, and the gain of the output screen is not directly affected by magnification alone.
Step-by-step explanation:
When using an image intensifier's magnification mode, there are several outcomes that can be expected. First, magnification increases the size of the image, though this does not necessarily mean that resolution increases. In fact, magnifying could potentially spread the available resolution over a larger area, making details less crisp. Second, the use of a higher magnification mode requires increased input radiation to maintain image quality, which consequently leads to an increase in patient dose. Third, the output screen gain is not inherently increased simply due to magnification; gain is related to how well the image intensifier converts the input radiation to light on the output screen. Therefore, the correct answer to whether output screen gain is increased, resolution increases, and patient dose increases when an image intensifier's magnification mode is used, is D. 1 and 3 only.