I had one today. Was told it's normal and was there for the reason that if I had to have further exploration the nurses would be able to find the exact place to look.
I asked if it would sound alarms at the airport but was told no. x
I was recalled for further views after yearly mammograms showed areas of calcification. Had core biopsies to both breasts and at the end a titanium marker was placed in each breast to show where the biopsies had been taken. Is this normal practice ?