Only in the U.S. could they have a breast milk scanner at the airport. The quick summary: you can take breast milk as hand luggage, even though you're traveling alone. Boston airport has private bathrooms where you can pump, Pittsburgh airport does not.
I'll step back for a second-- I had some fears about traveling for the day to Pittsburgh, mainly around pumping and traveling with milk.
Some things were helpful and some things less helpful in dealing with these fears. Least helpful were the websites that reported that you couldn't take breastmilk in your hand luggage unless you had a baby with you (which, I know, doesn't make sense, and goes to show I shouldn't believe everything I read.)
Most helpful was a) taking my fears to their logical conclusion, and seeing if they're all that bad. So, what if I wasn't able to find a space to pump all day, and as a result Noah had to have formula at some point in the next month (we've not bought formula up to now), or I had to dump milk or... Not great outcomes but also not absolutely earth-shattering.
b) Not being embarrassed to ask security before checking in. I went to security in both Boston and Pittsburgh, explained my situation and asked for their suggestions. On the Pittsburgh side, they had a scanner for the milk, and were super polite about scanning and allowing me to travel with the milk as hand luggage.
Anyway, so my fears came up empty. I did have to pump in a large banquet room in a hotel, where I was locked in from the outside, which was vaguely uncomfortable, but makes for a pretty good story...I'm glad to be back at home, with Noah and Eug.