Hi Miriam~ I also had a recent call back for additional images and ultrasound after my routine mammogram. At that appointment the radiologist requested a biopsy. After the biopsy I was diagnosed with atypical lobular hyperplasia in one breast. (Pre cancerous cells) They said standard procedure at that point is to visit a surgeon, which I did and he ordered an MRI. All of these appointments took about 6 weeks and basically because I have dense breasts that they couldn’t see into. My only risk factor was 5 years of HRT. I am post menopausal. If they see anything suspicious at your ultrasound I would think this will be the sequence for you as well. Only a small percentage of call backs result in a cancer diagnosis so try not to worry too much.