You nailed it. I was trying to find a way to express what I meant and all I could think of was circulate. So that means it would just "sit" at a certain area and the doctor could probably determine from that right?
Try this: A sump pump. It's not working and you have a pool in the basement. Add a bucket of DYED water, and you can visibly see it one area because nothing is moving. If the pump turns on it will start to intermix but still be generally located where it was dumped in.
Using dyes is common in Engineering and it is often used to see if someone is "dumping" into a water source.