Two-part question about sexual thoughts

Part One - Do sexual thoughts affect the reboot?
I currently have 26 PMO-free days under my belt, so this streak is going pretty good. The one thing I find myself plagued with though are sexual images flickering through my head like slides on a slideshow. It's the same ones, and I don't dwell on them, but at least a few times an hour for a few seconds I find them being mentally projected in my head. They don't lead to an erection, and the feeling isn't all that similar to actually watching P. I do wonder though, do these momentary thoughts hinder one's reboot, if they're consistently briefly thought about throughout the day?

Part Two - What's the best way to react to these thoughts?
I feel like the more I try to fight them off and tell my mind "NO!" the more often I get them. But then obviously if I dwell on or entertain them then I'll find myself being aroused and the dopamine will flow. What's the alternative to best deal with these thoughts and reduce how often I find myself thinking about them?