What is this measurement on my ct?

Hi there! I’m 33f, ended up in the emergency room yesterday and diagnosed with diverticulitis. I was looking at my CT out of curiosity (saw the two very white spots where my infections are) and noticed on one of the frames that there is a measurement!

I’m not worried or anything, just curious what it is! Thanks

https://imgur.com/a/rMb9gIX