I found this video very informative regarding vasculitis and the lungs.
He mentions that dipping your urine with Hemastix regularly can help us determine a flare because an attack on the kidneys will result in blood in the urine.
These strips will only work if you don't normally leak blood in the urine.

He also, says that the CT and xrays only see nodules and cannot tell if they are granulomas or blood clots except if they cavitate.

https://www.youtube.com/watch?v=DTmL3XInkYg