How Is Sound Produced in Ultrasonography?

Ultrasound technology saves lives, yet for most of us, the way it works remains a mystery. The process must have something to do with sound waves (it is called ultrasound, after all), but for those of you who dropped physics before the teacher could get to Newton's third law of motion, the rest might seem better unexplained. You will find that the magic of ultrasonography is actually much more straightforward than you might expect.

Signal Generation

• Thanks to an under-appreciated little effect called piezoelectricity, some crystals become electrically charged when put under pressure. Some examples of such crystals are quartz, and barium titanate. In the case of medical ultrasonography, the piezoelectric crystal subject to pressure is typically lead zirconate titanate--used in the device attached to the wand that glides against the body during an ultrasound exam. Because of all the pressure to which the lead is being subjected, it responds with a mechanical vibration. This is the first signal generated in the ultrasonography process.

Transduction

• That mechanical vibration needs to be translated into a language that can be communicated through the body, and that language is the language of sound. The wand gliding over a body serves as the translator, or the transducer, and its job is to convert the vibrations into extremely high-frequency sound waves, within the range of 1 to 20 MHz. These sound waves then make their way through the body, creating echoes when they hit solid structures, like fetuses or gallstones.

Reception

• The same device that transduces the original electrical signal into ultrasound waves also happens to be the device that is capable of receiving that signal when it bounces back towards it. The sound waves that have traveled through the body, having been reflected back, are now ready to be interpreted by the transducer and translated back into electrical signals.

Imaging

• These electrical signals are then sent to a computer, which is designed to translate them into on-screen images to be read by the ultrasound technician. These images offer a visual representation of the internal body based on how strong and how loud the returning sound signals were, as well as how quickly the signals returned from the patient's body to the transducer.

Usage

• Ultrasonography is widely used for diagnostic purposes because of its non-invasive nature. Unlike other diagnostic tools like X-rays or CT scanners, ultrasound does not expose the body to dangerous radiation, making it a much safer alternative when other diagnostic tests are not necessary. According to the U.S. Department of Health and Human Services, it is routinely used for fetal imaging, as well as osteoporosis diagnosis, echocardiology, blood flow imaging and even ultrasound-guided biopsies.