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 when an applied voltage deforms these materials. Single element transducers are thus made up of a piezoceramic disk, which expands when the current is reversed. With direct current, if the pressure is applied to the disk, voltage is produced; if the alternately current can also be used, in which case the disk alternately expands and contracts. Based on the principle of the piezoelectric, alternating pressure on the disk likewise produces an alternating voltage. (Farr and Allisy-Roberts 185-86).
Transducers are used in either pulsed or continuous wave modes, corresponding to the use of direct current or alternating current, respectively. Pulsed modes are basically used for imaging, while continuous wave modes are primarily used for therapy. In a continuous wave mode, the disk on the transducer expands and contracts back and forth, creating a continuous wave with the same frequency as the vibrating...