Final answer:
Fluoroscopic grids are located between the patient and the image intensifier to reduce scattered radiation. High ratio grids are preferred, but the typical ratio is 8:1 or 10:1.
Step-by-step explanation:
Fluoroscopic grids are located between the patient and the input layer of the image intensifier, which is statement 1. They are used to reduce scattered radiation produced in the image intensifier, supporting statement 2. Regarding statement 3, high ratio grids are indeed preferred because they provide better scatter reduction. However, the typical grid ratio is 8:1 or 10:1, not 12:1 as stated in statement 4.