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The ultrasound machine consists of two main parts, the probe and the processor. The probe is the “brawn” and the processor the “brains” of the operation. The probe has two main functions: first, to generate a sound wave (acts as a transmitter), and second, to receive a reflected sound wave (acts as a receiver). The processor, located within the ultrasound unit, takes these incoming signals and turns them into a useful image.

The transmitter and receiver functions of the transducer do not occur simultaneously but rather sequentially. When placed under mechanical stress, the ceramic crystals in the transducer generate a voltage. This process, known as the piezoelectric effect, occurs during the receiving phase, which is when returning sound waves strike the transducer. When an external voltage is applied to the crystals, they exhibit the reverse phenomenon and undergo a small mechanical deformation. The subsequent release of this energy generates the ultrasound wave. This is known as the reverse piezoelectric effect. World War I saw the first practical use of the piezoelectric effect in the development of sonar using a separate sound generator and detectors (Coltrera 2010).

The sound waves generated by diagnostic ultrasound machines are typically in the 3–14 megahertz (MHz) range and are thus too high pitched to be perceived by the human ear. We can hear sounds in the range of 20 Hz (cycles/second) to 20 000 Hz. In contrast, our average canine patient hears sounds in the range of 40 Hz to 60 000 Hz. The high frequencies are in the realm of what is termed the “ultrasonic” range, basically any sound above our ability to hear and hence the name for this clinical imaging tool (Nyland et al. 2002).

The sound waves produced by the transducer penetrate the body tissues and are subject to all the rules surrounding any sound wave, including reflection, refraction, reverberation, attenuation, and impedance. The processor analyzes the transmitted signals and the returning waves, including their quantity, strength, and the time they took to return. By applying preprogrammed algorithms, the processor translates this information into a pixel, gives it an appropriate intensity (its echogenicity), and places it on the monitor screen to give us the image (sometimes being “fooled” into creating artifacts).

Between the transducer and the processor, it is easy to see why the equipment for this modality can be rather pricey. However, by using the variety of POCUS and FAST ultrasound exams outlined in this textbook, we hope that your ultrasound machine will become an asset not only with improved patient care but also with a return on investment.