Well, as I noted in the thread about insurance companies and scans, they wouldn't let me have an MRI, so I had a "triphasic" CT scan instead. This is supposed to do a better job of imaging the liver. Apparently the dye is taken up in the arterial system and portal veins at different times, and what they do is take two sets of images timed to hit each phase. The two phases are less than a minute apart.
Lo and behold, it would appear that it actually worked better than the standard CT. The radiologist was able to see the presumed met, and by some kind of measurement wizardry compare the size to the MRI. He said it was "Substantially unchanged." The two enlarged lumph nodes in the porta hepatis, which were what I was most worried about, have shrunk down to normal size. Yeah! Apparently Keytruda is working!
There are no new issues.
Now I'm wondering if it is possible that the node is dead. I plan to push for having it removed, which should be possible laparscopically, I hope, because it is small, subcapular, and not near anything important. I'd be interested in other people's opinions and experiences with this kind of thing.