I had my first mammogram at the age of 40. I was asked to do a follow-up the next day to do a diagnostic mammogram and ultrasound on my right breast only. The radiologist indicated I have very dense breast and recommended a 6 month follow-up on that right breast. I asked if there was something specific that concerned her but she seemed to indicate it was more she just couldn't see and that since it was my first one, she had nothing to compare it to. Needless to say, it concerned me. Is this common/not common?