Ultrasound imaging, also called sonography, is a method of obtaining images inside the body using high-frequency sound waves. There is no radiation involved in ultrasound imaging, and there are no known harmful effects to the human body. Ultrasound is perhaps best known for providing expectant parents with the first picture of their unborn child. Ultrasound images are captured in "real time" and they can show the movement of a fetus as well as complex bodily functions such as blood flow and heart valve operation. The procedure is also used to guide needle biopsies, in which needles are used to sample cells from certain organs or tissue for laboratory testing.