WHAT IS ULTRASOUND? Sound is a pressure wave that causes the air around it to vibrate. The rate at which these fluctuations occur determines a sound wave's frequency. The human ear can interpret an impressively broad range of sound frequencies -- everything from a whisper to the roar of a jet engine -- but ultrasound uses such high frequencies (between 1 and 5 megahertz) that the fluctuations in the pressure wave are too fast for us to detect.
ABOUT BREAST CANCER: Breast cancer is a type of cancer in which cells in the breast become abnormal and grow and divide uncontrollably, eventually forming a mass called a tumor. Some tumors are benign, meaning that they do not invade other types of tissue, although if they become big enough, they can interfere with some bodily functions, such as the flow of blood or urine. Malignant tumors have cells that can invade nearby tissues. When a cancer "metastasizes," cells from the original tumor break off and travel to other parts of the body via the blood or lymph systems. More than 75 percent of breast cancers begin in the milk ducts within the breast. The next most common site is in the glandular tissue that makes the milk.
The American Association of Physicists in Medicine and the Optical Society of America and the American Physical Society contributed to the information contained in the TV portion of this report.
