Ultrasound therapy involves production of longitudinal mechanical waves above the audible range (20 KHz). The frequencies used in physiotherapy vary from 0.75 MHz to 3 MHz. These are produced by distortion of quartz crystal, by a high frequency alternating current.
These sound waves require a conducting medium like oil or water to reach from the probe head to tissues. The probe head should be applied perpendicular to tissues to present refraction and it should be moved continuously to prevent concentration on one tissue area. Higher the frequency, greater the absorption and smaller the depth of penetration.
Guidelines for treatment
- Superficial lesions are treated with 3 MHz frequencies.
- Deeper lesions with 0.75-1.0 MHz frequencies.
- For acute injuries, starting dose may be 0.25 Wcm* for 5 minutes twice daily. Progression is made by increasing the time and reducing the frequency of treatment.
- For chronic problems, the intensity may be increased up to 1 Wcm*.
Indications
- Indications are same as short wave diathermy.
- Ultrasound therapy is speculated to help by release of chemical mediators, improving perfusion and mobilization of phagocytes and macrophages to reduce oedema.
*Wcm is unit of power intensity of ultrsound
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