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Ultrasound application has evolved from what was once a rote "cookbook" approach to a clinical science. Determining if ultrasound is indicated and, if appropriate, the proper output parameters requires knowledge of the type of tissues involved, the depth of the trauma, the nature and inflammatory state of the injury, and consideration of the skin and tissues overlying the treatment area.
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• Although some treatment parameters have been established, patient feedback and reevaluation of the response to prior treatments form the basis for adjusting the treatment parameters. Inform the patient about the expectations and sensations that are to be expected during the treatment and inform the patient to report any uncomfortable, unusual, or unexpected sensations such as pain or burning.
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To ensure safe application of therapeutic ultrasound, units must be calibrated at least once a year (many manufacturers recommend that this be done twice a year). The U.S. Food and Drug Administration (FDA) requires that the output frequency, effective radiating area (ERA), and beam type must be indicated on the generator or the transducer10 (Fig. 8-1). The date of the last calibration must also be indicated somewhere on the unit. The reported ERA is the average for that make and model; the actual ERA may be significantly different from the reported value.11 The size of the transducer face may also be included if it is significantly different from the size of the ERA (see Fig. 7.1).1
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Tissue Treatment Area
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Ultrasound can only increase tissue temperatures when the treatment area is approximately two times the size of the ERA.8 Note that the ERA is approximately half the size of the transducer face. Attempting to heat a larger area will significantly reduce the temperature increase. If the size of the target tissues is larger than three times the ERA, divide the area into two or more treatment zones (Fig. 8-2).
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