CT protocols

Hello Radiology nurses, hoping you can give me some insight.

1. Our facility protocols require 2 hours between oral contrast administration and a scan of abd/pelvis. The same applies when oral contrast is administered via g-tube or j-tube. I can't get anyone to explain why 2 hours is still needed. I would think that administering the contrast that much further along the GI tract would decrease the prep time. Any thoughts?

2. Do you have any problems using saline locks w/J-loops, extension sets, what-have-you for power injections of contrast, or do you require the lock to be capped with a luer lock only? What is the rationale? From my perspective, the tubing of the extension set is larger than the actual IV cannula, so I can't imagine why it would cause a problem.

Thanks in advance.