For a lateral knee projection, what size cassette should be used?

The correct choice for the size of the cassette used in a lateral knee projection is 10" x 12". This size is appropriate because it allows for adequate coverage of the knee joint while minimizing the amount of unnecessary radiation exposure to surrounding tissues. The lateral knee projection is specifically designed to visualize the joint space, the alignment of the femur and tibia, and any potential abnormalities.

Using a smaller cassette like 10" x 12" helps focus on the area of interest, providing a detailed image of the knee without including excessive peripheral anatomy that larger cassettes would capture. This is particularly important for ensuring that the image quality is high and that the structures of the knee can be evaluated effectively. Larger cassette sizes could introduce unneeded radiation exposure and could complicate positioning.