Chapter 22

• Ultrasonography is the imaging of choice for confirmation of pyloric stenosis, testicular torsion, ectopic pregnancy, ovarian torsion, and appendicitis.
• High clinical suspicion for testicular torsion or ovarian torsion should not be ignored when not confirmed by ultrasonography. Sensitivity and specificity is limited.
• Successful diagnosis with ultrasonography may be limited in obese children.
• Computed tomography is an extremely valuable imaging tool, but the risk of ionizing radiation exposure should be considered when ordering this test in young children.
• MRI in the ED is usually reserved for emergent conditions such as cord compression and stroke.

The practice of emergency medicine brings patients with a variety of complaints to our doorstep. In deciphering the many signs and symptoms, the art of medicine comes into play when trying to reach a diagnosis. Technology has allowed us a more innovative method to confirm a diagnosis with various imaging studies. This chapter will review the most commonly available imaging modalities and discuss the various considerations for optimal visualization and patient safety.

Ultrasound technology was first commercially available in the late 1960s as a rigid contact B-mode machine.1 These early machines were able to take still pictures only, thus had limited usefulness in the emergency department due to the time and labor-intensive nature of the equipment. In the late 1970s, the first real-time ultrasonography machine was introduced, and by the mid-1980s ultrasound machines started to be used in the emergency department (Fig. 22–1).1,2 By 1996, the American College of Emergency Physicians founded the Section of Emergency Ultrasound to promote further advancement in this field.2Figures 22–2 and 22–3 provide an approach to the use of imaging for pediatric trauma victims and medical diagnosis in children.

###### Figure 22-1.

Picture of typical ultrasound machine.

###### Figure 22-2.

Trauma imaging algorithm.

###### Figure 22-3.

Medical imaging algorithm.

### Physics and Pathophysiology

Ultrasound employs sound waves, a form of nonionizing radiation, to visualize internal structures. As sound travels through the tissue, the molecules are compressed and decompressed. An isolated compression and decompression event is defined as one cycle. The number of cycles that occur over time is termed the frequency. Frequency is measured in hertz (Hz), where one hertz equals one cycle per second. Diagnostic ultrasound uses frequencies from 2 to 10 MHz (2–10 million cycles per second), which is considerably above the threshold that human ears can hear.2

The picture generated by the ultrasound machine is a result of various elements working together. The transducer, also known as the probe, is the portion of the machine that is held by the examiner to the patient's body. A linear ...

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