What is the difference between an mammogram and a ultrasound?

Mammo vs ultrasound. A mammogram is a low dose X-ray of the breasts. An ultrasound utilizes sound waves to generate images.
Screen v. Diagnostic. A screening exam is done on anyone at risk for a disease in the absence of any symptoms. A diagnostic exam is done to evaluate a specific abnormality. Mammograms are effective screening and diagnostic studies; an ultrasound is most useful as a diagnostic test.
Imaging. Different imaging studies. Mammogram is usually to see breast tissue. If there is any cyst in breast sometimes ultrasound is ordered to see if this is fluid filled cyst or solid to differentiate.
Different techniques. They are different technologies/techniques to view breast tissue. They both have important roles in looking at breast tissue.
X-ray vs sound waves. If you have a lump that can be felt, it's likely the radiologist will want an ultrasound as well as mammogram. Mammogram uses x-rays to see calcifications that might indicate a breast cancer, while ultrasound uses sound waves to see different characteristics of breast tissue such as blood flow, size and shape of a lump and whether it's solid or cystic. Ultrasound is also used to guide biopsy.

Related Questions

I want to know what is the difference between mammogram and ultrasound when it comes to breast cancer detection?

"Apples and Oranges" A mammogram is an excellent (and inexpensive) screening test, meaning that it is designed to find cancers too small to detect by palpation. In contrast, ultrasounds are diagnostic tests, meaning they are helpful to determine whether an abnormality seen on a mammogram (or exam) is worthy of a biopsy. For example, one can only distinguish a cyst from a tumor by ultrasound.
Xrays vs ultrasound. Mammograms are images obtained by compressing the breast and exposing the breast tissue to x rays from several directions. Various findings on these X-ray images could be a sign of cancer. Ultrasound images are obtained by sending high frequency sound waves into (breast) tissue and capturing reflected sound waves back. These are then used to generate an image. Breast cancer can often be detected.
X-ray mammograms. Rely on difference between tumor and tissue (not there in the 15% with inv lobular ca until quite large), requires compression (universally hated), and leads to u/s for biopsy direction, and sometimes mr. 3 tests: one relatively insensitive, one not reliably reproducible, 1 fraught with false positive.

What's the difference between mammogram and ultrasound for breast cancer detection?

What they see. Mammograms use x-rays to evaluate the breast. They look for abnormal deposits of calcium that can be a sign of breast cancer. Ultrasound is used for lumps for which the significance is uncertain. Ultrasound can tell the difference between fluid filled cysts (that are benign) and solid masses that should be biopsied. This is especially useful in younger women where cysts are common.
Complementary. A mammogram is an excellent screening test, designed to find cancers before they are palpable. An ultrasound is best utilized for determining the severity of what was seen on mammography. Using the info from both studies, we can then decide if biopsy is necessary. Ultrasound is also a tool to supplement physical exams--it's like a stethoscope for breast surgeons.
Mammo/ultrasound. Across the board, screening mammography detects approx. 3-5 cancers per 1000 patients. Some studies show that screening ultrasound can detect an additional 2-3 cancers per 1000, and is particularly particularly useful in dense breasts, where the sensitivity of mammo for detecting cancers drops from 80% overall to less than 50%. They are complementary tests, and the role of US is currently evolvin.