- In addition to radio and television, which use the range of frequencies that we can hear, we have devices that can use frequencies beyond our ability to hear called ultrasonic sound. Radar and sonar are two applications of this type of sound. A third, ultrasound, or medical sonography, was developed by a doctor in the 1960s and was inspired by a dental tool that used ultrasound to clean teeth.
- Medical sonography works like other ultrasonic techniques. It generates a sound wave, bounces it off something and records the returning sound. As a diagnostic tool, ultrasound is noninvasive, gives clear results and poses no risk to the patient when used by a trained medical professional. The technology, unlike magnetic resonance imaging or X-ray equipment, is fairly simple to operate and relatively inexpensive.
- The basis for medical ultrasound begins with the Curie brothers' studies of the properties of crystals in the nineteenth century. Their discovery that compression of certain crystals produced an electrical discharge began the line of inquiry that led to sonar in World War I, radar in World War II and that dentist's plaque-blaster. All ultrasound begins with a piezoelectric transducer, an instrument that compresses various types of crystal or ceramic between metal plates until it emits a high-frequency sound wave.
- Most medical ultrasound uses ceramic transducers that emit a wave frequency between 2 and 18 megahertz. A technician directs the sound using a wand-like device that bounces the sound out and receives the echo as the sound bounces back off internal organs, tissue and bone. A warming gel on the skin of the patient removes the possibility of false echoes from the skin itself. The type and quality of the returning sound defines the distance from the transducer and its shape and density. The vibration of the transducer plates generates electric current that is translated into a digital signal in the scanner. Software then translates the signals into a picture and data. Since sound waves radiate from a source, the resulting pictures are cone-shaped.
- Medical sonography is most commonly associated with fetal development because of its ease of use and safety. Sonograms can spot congenital physical problems as well as potential multiple births. Sonograms are used frequently in gynecological and oncological examinations and can be used in places where visual examinations are problematical. Modern sonography has developed applications using Doppler theory to show movement, speed and sound. Multiple, or phased array, transducers allow technicians to adjust the sonogram to reveal different aspects and depths.
