Page 16 - Ultrasonography in Prehospital and Emergency Medicine - Rein Ketelaars

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Chapter 1
A transducer contains a series of piezoelectric crystals that can convert electrical energy into ultrasound waves. These crystals can also receive the reflected ultrasound and convert it back into electrical energy that can be processed by the ultrasound machine’s CPU to produce an image on the monitor.
The transducer is positioned on a body surface and the ultrasound waves are then conducted by tissues or fluids in the body. They are reflected back to the transducer to varying degrees by any structure they encounter. The greater the difference in conductive properties between adjacent tissues and fluids, the greater the proportion of ultrasound that is reflected by these tissues or fluids. Air and bone are the strongest reflectors. The reflected ultrasound waves are received by the transducer and used to construct an image of the area of interest. For instance, this same principle is found in nature (Figure 1.1) and marine technology (Figure 1.2). Examples of ultrasound images in medicine are displayed in Figure 1.3 and Figure 1.4.
Figure 1.2 Sonar image of the wreckage of the 1500 dwt German oil tanker “Holmengraa” It is lying on the slanted seabed off Horten, Vestfold, south of Oslo, Norway, at a depth of 77 m. It sank on 28
December 1944 as a result of an allied forces bombing. It was discovered in 1994. Reproduced with permission. Image copyright: Kongsberg Maritime.