It is not always necessary for clinicians to have a profound understanding of the technologies that they use. One need only consider studies such as impedance plethysmography (IPG), computed tomography (CT), and magnetic resonance imaging (MRI) to appreciate that the intricacies of even commonly used techniques are often poorly understood by the physician. Yet even with these types of examinations, to say nothing of electrocardiograms (ECGs), plain radiography, and radionuclide scanning, the physician who has a basic understanding of the manner in which the information is obtained and displayed is better able to interpret the significance of that information, particularly when complex or unfamiliar results are obtained. This is especially true when diagnostic ultrasound is used for the emergency department patient. In part, this is because diagnostic ultrasound in the symptomatic patient is inherently an interactive technique. Unlike the standard kidney, ureter, and bladder (KUB) examination, for example, which is performed in a standardized manner regardless of the patient's specific complaints or clinical presentation, the ultrasound examination of the abdomen will vary greatly according to the patient's clinical condition, specific complaints, unique anatomy, and symptoms elicited while performing the examination.

When used in this way—as an extension of the emergency physician's clinical examination—ultrasound is clearly the most user dependent of the imaging techniques. Although standard guidelines and protocols for the performance of ultrasound examinations by the traditional ultrasound specialist and technologist serve as useful guides, the ultrasound examination of the symptomatic emergency patient frequently leads the careful examiner to scan adjacent and even distant regions from the organ that was initially suspected. To accomplish this, nonstandard views are often required, and unfamiliar images that represent normal anatomy, abnormal anatomy, and artifacts are often obtained. In addition, particular characteristics of the instrumentation used may also lead to artifacts or unusual representations of anatomy; these effects may or may not be avoidable. For all these reasons, a basic understanding of the manner in which ultrasound waves can be used to form images is not merely an intellectual exercise: it has practical, clinical applications.