Ultrasound produces sound waves that are beamed into the body causing return echoes that are recorded to "visualize" structures beneath the skin. The ability to measure different echoes reflected from a variety of tissues allows a shadow picture to be constructed. The technology is especially accurate at seeing the interface between solid and fluid filled spaces. These are actually the same principles that allow SONAR on boats to see the bottom of the ocean.


How do patients prepare for an ultrasound?

UltrasoundPreparation for ultrasound is minimal. Generally, if internal organs such as the gallbladder are to be examined, patients are requested to avoid eating and drinking with the exception of water for six to eight hours prior to the examination. This is because food causes gallbladder contraction, minimizing the size, which would be visible during the ultrasound.

In preparation for examination of the pelvic  ultrasound, it is recommended that you drink at least four to six glasses of water for approximately one to two hours prior to the examination for the purpose of filling the bladder. The extra fluid in the bladder moves air-filled bowel loops and the organs are more visible during the ultrasound test.

Ultrasound imaging is based on the same principles involved in the sonar used by bats, ships and fishermen. When a sound wave strikes an object, it bounces back, or echoes. By measuring these echo waves it is possible to determine how far away the object is and its size, shape, and consistency (whether the object is solid, filled with fluid, or both).

In medicine, ultrasound is used to detect changes in appearance of organs, tissues, and vessels or detect abnormal masses, such as tumors.

How does the procedure work?

UltrasoundIn an ultrasound examination, a transducer both sends the sound waves and records the echoing waves. When the transducer is pressed against the skin, it directs small pulses of inaudible, high-frequency sound waves into the body. As the sound waves bounce off of internal organs, fluids and tissues, the sensitive microphone in the transducer records tiny changes in the sound's pitch and direction. These signature waves are instantly measured and displayed by a computer, which in turn creates a real-time picture on the monitor. One or more frames of the moving pictures are typically captured as still images.

Doppler ultrasound, a special application of ultrasound, measures the direction and speed of blood cells as they move through vessels. The movement of blood cells causes a change in pitch of the reflected sound waves (called the Doppler effect). A computer collects and processes the sounds and creates graphs or color pictures that represent the flow of blood through the blood vessels.