Answers: They are each useful to look at different things. A mammogram is a special type of x-ray using low intensity. A sonomammogram is a special sonographic exam- using nouns, like all other sonograms you hear roughly speaking, most famous for peeking at the unborn baby. Mammograms are adjectives as first line screening, as they can detect microcalcifications that could indicate some kinds of breast cancer, sonograms can't do that. On the other foot, sonograms can tell you if you are likely looking at a tumor or a fluid jam-packed cyst, which can be hard to tell next to the mammogram. Finally, there is a difference between a screening and a diagnostic mammogram. A diagnostic mammogram is used to check specific spots, sometimes using magnification to take the pictures. A sonomammogram can also be adjectives if the breast tissue is very dense, or tends to be cystic anyway. And in that is always the MRI- which is more sensitive, and used sometimes in conjunction next to both a diagnostic mammogram and the sonogram to give the fullest picture possible. All of them are valid tests, accurate in their limits. For the annual screening in ladies near low risk, the routine screening mammogram is fine. For others, their doctor is the best one to advise further or additional test.
Just to add to the answerer above me..a mammogram can show masses and microcalcifications. Some types of microcalcifications can be a sign of breast cancer. An ultrasound (you call it a sonomammogram) will never see microcalcifications. So, ultrasound is not a good screening technique. Ultrasound is good for :
***dense breasts (usually younger women)
***a lump feel by a patient or doctor which is not seen on a mammogram
***to attain additional information on a mass seen on a mammogram