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Machine Characteristics for Bedside Use
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Deciding on the type of ultrasound machine to obtain for your emergency department depends on balancing the cost versus the features desired on the machine.
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Early portable ultrasound units had the advantages of low cost and user-friendly interfaces with limited adjustment options. Small viewing screens were problematic, and multiple probes could not be used simultaneously. Image quality was reduced but battery power and rapid power-up allowed immediate imaging.
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Traditional, larger ultrasound machines commonly used by radiologists are designed for the radiology suite, where patients are brought to the machine. There are obvious disadvantages in bringing these to the patient bedside in a crowded emergency department, and many have a prolonged power-up period causing a delay in image acquisition. The cost of these machines is also prohibitive in most emergency departments.
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Ultrasound machines designed specifically for bedside applications are now available. Small physical profiles, digital storage, fast power-up, multiple probe ports, and high-quality images are made possible by technological advances. Basic features ideal for the emergency department setting are listed in Table 6–1.
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There are three main types of ultrasound probes or transducers: curved, linear, and phased array (Figure 6–1). Curved probes are used for abdominal and obstetric imaging. Linear probes are used for soft tissue and small parts imaging. Phased array probes use computer control to “bend” the ultrasound beam from a flat, small footprint to a wider pie-shaped wedge distally. This is usually called the “cardiac” probe but is also excellent to image between ribs and is often used for abdominal imaging.
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Many ultrasound probes allow for use of variable frequencies. Curved array probes used for abdominal imaging, for example, may have settings from 2.5 to 5 MHz. Soft tissue probes and intracavitary/transvaginal probes may allow for settings above 7 MHz. There is an inverse relationship between the resolution of a probe and its penetration.
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Most emergency departments will require a minimum of three probes, depending on the types of ultrasound examinations and procedures anticipated (Table 6–2): one for abdominal imaging, one for high-resolution shallow imaging, and an intracavitary probe. While more probes would seem beneficial, the probes make up a large portion of the cost of the ...