I had two, so I feel like I am qualified to answer this in the club you never wanted to join. I had the radioactive isotope injected first. This took a little while because they had to bring it in after they had me in radiology. Then the machine to track it was broken so they gave me a shot of the blue dye, which resulted in my husband calling me Smurfette for months. Lol. These were both injected directly to the spot of the tumor, so that they could track where it drained to and find the sentinel node. It was not painful at all, but it did take a while. When is your surgery?💜