For a radiograph of a pelvis that is elevated off the image receptor, what is the smallest IR size needed to capture a 16-inch wide pelvis?

To determine the necessary image receptor (IR) size required to capture a 16-inch wide pelvis effectively, it's essential to consider that the IR needs to exceed the width of the object being imaged to prevent any clipping of the anatomical structures. A pelvis measures 16 inches across, which indicates that the IR must be at least this size to encompass the entire width without losing any detail at the edges.

The correct choice reflects the need for the IR to slightly exceed the object's dimensions to ensure complete coverage. An 18-inch IR size provides the necessary buffer, allowing for any potential movement or positioning variances that might occur during the imaging process. The additional space ensures that the anatomical structures are fully captured within the radiograph, assisting in accurate diagnostic assessment.

Smaller IR sizes, such as 12 or 16 inches, are inadequate in this context, as they would risk cutting off parts of the pelvis in the resulting image. The larger choices, like 20 inches, while adequate, provide more excess space than required, making 18 inches the most suitable and efficient option for this scenario.