Is a breast ultrasound better than a mammogram?

My doc recently told me that an ultrasound is best for YOUNG women with more dense breast tissue. I had an area of lumpiness(which she deemed benign) but at 38, she recommended an ultrasound to check this out rather than a mammogram, which she said is more useful for older women.

There are differences to what mammograms and ultrasound can see, and so they are considered complementary procedures. Apparently mammography is better in "spatial resolution" -- or detail -- and in seeing microcalcifications. Ultrasound has more contrast, and so it's better at detecting what a specific breast mass may be made of (such as a fluid-filled cyst, which looks very different to an ultrasound picture than the breast tissue surrounding it). It's also useful in studying breast conditions in younger women, whose breast tissue is very dense.

Here's a page in which both are discussed:

http://www.imaginis.com/breasthealth/ultrasound.asp

Perhaps the doctor has had more diagnosis success with the ultra sound than the mammogram. Most protocol is mammogram first and then if uncertain, an ultrasound. Insurance companies prefer this chain of events. Some insurance companies are balking at MRI for high risk patients, which is a newer tool in the diagnosing bag.
Keep in mind that doctors don't want a lot of call backs from insurance companies. I think a bit of proactive advise is to check what your insurance will cover and for what diagnosis.

Did the doctor explain why she thought an ultrasound is better than a traditional mammogram? An ultrasound bounces a signal off the tissue, creating a graph that would show a mass, if there is one. Perhaps this is a more comfortable method of examination?

Here's some information on breast ultrasounds from the Radiology Information site.