With the pressure, tissues are literally being pushed aside so that the tissues can be better seen. Hope this helps.
It can be, and often it is better seen on an ultrasound. From what I have been told ultrasounds cost more to do and that is why they don't do them first. Personally I think that is a bogus reason. If you are trying to prevent breast cancer, why are they exposing women to radiation when there is a better way?