The Physics of Ultrasound

Without the use of physics in the medical field today, diagnosis of problems would be challenging, to say the least. The world of medical imaging in particular has benefited greatly from the use of physics.

Ultrasound is sound waves that have a frequency above human audible. (Ultrasound Physics and Instrument 111). With a shorter wavelength than audible sound, these waves can be directed into a narrow beam that is used in imaging soft tissues. As with audible sound waves, ultrasound waves must have a medium in which to travel and are subject to interference. In addition, much like light rays, they can be reflected, refracted, and focused.

In general, ultrasound waves produced by an instrument called transducer are sent into a patient. Some of the waves are absorbed, but the other portion of these waves are reflected when tissue and organ boundaries are encountered. The echoes produced by the reflected waves are then picked up by the transducer and translated in a visible picture often referred to as ultrasound. In the paragraphs that follow, the physics of how the transducer functions, what the ultrasound waves do, and how the image is formed will be explained.

A transducer is a mechanism that changes one form of energy to another form. A toaster is a transducer that turns electricity into heat; a loudspeaker is a transducer that changes electricity into sound. Likewise, an ultrasound transducer changes electricity voltage into ultrasound waves, and vice versa. This is possible because of the principle of piezoelectricity, which states that some materials (ceramics, quartz, and others) produce a voltage when deformed by an applied pressure. Conversely, piezoelectricity also results in production of a pressure whe...

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Ultrasonic images are produced by pulsed ultrasound beams and displayed by a system consisting of a beam former, transducer, signal processor, image processor, and display (Kremkau 354). In pulse echo imaging, the transducer converts the electric pulses given off by the beam former to an ultrasound beam. The transducer gives off several cycles of ultrasound beams and then waits to gather information from the echoes of those beams before giving off the next cycle of beams, this delay is necessary in order to escape misplacement of the returning echo on the screen (Kremkau 103).

In summary, the medical imaging technology of ultrasound is founded on the world of physics. As we understand more and more about waves and how they functions, ultrasound imaging capabilities expand, allowing for the increasingly accurate diagnostic of medical problems.