I have very dense breasts too. I had an ultrasound last week after a mammogram because I’d been feeling strange pains for a month in my left breast. The ultrasound showed suspicious looking tissue so they did a core biopsy (big hollow needle). The radiologist gave me 5 injections of Lidocaine to deaden my breast, and I just felt the first one-tiny prick. My breast was totally numb so I didn’t feel anything when she put the core needle in to remove 4 tissue samples. I’m still very sore now but getting better. They found invasive ductal carcinoma so I’m glad they did the biopsy. I had DCIS 12 years ago in the same breast. Hopefully, your biopsy may show nothing.