Another interesting alternative: the pill camera. You fast, swallow a pill containing a camera, a bright LED and a battery, a video is transmitted through your body recorded by a sensor outside, and someone qualified can glance if anything is wrong.
Pill teardown here [1], images here [2] (without fasting).
The upside is quite clear, especially if you are already used to fasting. The downsides are that you can't control the speed of the pill going through your digestive system, and if a polyp is found, you still need a colonoscopy to remove it (and need to fast again).