These days we know that X-rays, even the newer targeted beams, produce “scatter” and that doesn’t just mean peripheral radiation that bounces around in the room the machine is in. It’s been discovered that the scatter also happens when radiation from an X-ray (or CT scan) ricochets around inside your body. The current thinking is that a lead apron may trap some of that radiation inside your body and that it gets absorbed into tissue beyond the area being imaged. In that way shielding might actually increase your level of radiation exposure. This scatter can also degrade image quality.