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 has an impressively broad range of sound frequencies that it can hear -- 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. Ultrasound uses principles similar to RADAR and SONAR, except that the medium doing the reflecting is the human body. Ultrasound machines transmit high-frequency sound pulses into the body using a probe. The sound waves travel through the body and bounce off any boundaries, such as between fluid and soft tissue, tissue and bone. Some of the sound waves are reflected back to the probe, while others travel further through until they bounce off another boundary. All the reflected waves are recorded by the machine, which then calculates the distance each sound wave traveled based on how long it took the sound wave's echo to return. This data is used to form a two-dimensional image based on the distances and intensities of those echoes.
ABOUT PREEMIE BRAIN DAMAGE: Roughly half of premature births show subtle abnormalities in the brain that may be linked to later developmental problems. Yet it is often difficult to spot this damage early with traditional ultrasound; often problems don't become apparent until around 10 months of age. The possible causes of brain damage in premature infants are not fully established, but include infection stemming from the wall of the uterus or placenta; the inability of an immature cardiovascular system to pump enough oxygen-rich blood to the brain; and an inflammatory response at birth. The Monica AN24provides the kind of data that helps doctors spot danger signs earlier, allowing them to respond quickly when necessary.