An Introduction to Ultrasound Equipment and Knobology

Key points

US machines

The fundamental principle of ultrasonography can be traced to approximately 200 years ago when Lazzaro Spallanzani, an Italian biologist, theorized that bats used echolocation to hunt in the dark.¹ During the late 1800s, the concept of sound was expressed mathematically by the English physicist Lord Raleigh.² In 1880, the piezoelectric effect of crystals was first described by Pierre and Jacques Curie.³ These principles in physics were initially incorporated into industrial applications (eg,

US probes

Although there are many US transducers designed for specific uses in medical practice, most of POC ultrasonography can be accomplished using one of four basic types of probes: (1) curvilinear, (2) linear, (3) sector/phased, and (4) intracavity (Fig. 9, Fig. 10, Fig. 11, Fig. 12).

The basic US transducer is composed of the head, the wire, and the connector. In most machines, the transducer is interchangeable by detaching it completely from the US machine base. Many POC US machines can be fitted

Image production and system controls

To produce US images for evaluation, the machine and probes work in concert to transmit, receive, and depict sound waves. The US machine receives the beam signal as amplitude, frequency, and the changes of the frequency over time. The two-dimensional gray scale of the image is generated from the amplitude of the echoes. The change of the frequency and wavelength of the US echoes from a target in motion is known as the Doppler effect. Further information about the physics of bedside US can be

Obtaining calculations on bedside US

During bedside scans, it is often useful to obtain specific measurements of the structure being evaluated. For example, measurements of the IVC diameter are being used to guide resuscitation attempts (Fig. 29). Most machines have a caliper button that allows the user to measure the absolute distance between two points. The select key is typically used to toggle between the two calipers. Once both calipers have been aligned along the border of the object being measured, the distance between the

Adjusting the depth of the scan

The penetration of the US beam on a particular transducer can be altered by manipulating the frequency of the probe and adjusting the depth or penetration button/knob on the US machine. The depth and penetration achieved during the scan are displayed as a scale on the left or right side of the US screen. By convention, these hash marks are designated at 0.1-, 0.5-, and 1-cm increments (Fig. 32). During the initial part of a scan, it is often useful to start with an increased depth for

Summary

Understanding basic US instrumentation and knobology is an important step in learning how to perform bedside US examinations. Although US machines may differ in some of their capabilities, the standard instrumentation and functionality remain essentially the same (Fig. 35). Becoming familiar with the machine and the controls used for image generation optimizes the scans being performed and enhances the use of US in patient care.