Ultrasound

Ultrasound is a form of acoustic energy utilized for thermal and non-thermal effects. To deliver these acoustic waves, there is an instrument with a metal faceplate containing quartz or crystals inside. When mechanically altered, they produce an electric output. Therapeutic ultrasound has been used to stimulate the repair of soft tissue injuries and to relieve pain.

For thermal effects to occur, energy must be absorbed. One wants to attain a deep penetration of the heat, with the optimum depth of penetration being 3-5 cm (as opposed to a heat pack, which heats only 2 cm deep). Non-thermal effects include micromassage (microscopic movement of fluids and tissues), which leads to an increase in membrane permeability and arterial vasodilation and constriction. The indications for thermal and non-thermal ultrasound are quite different, whereas the precautions are the same:

• Areas with decreased sensation and circulation
• Eyes, esophogus, reproductive areas
• Pregnancy
• Cancer
• Cardiac Pacemaker

Clinical applications of therapeutic ultrasound include:

1. Inflammation: Acute and subacute phases
   • Utilized at low intensities to promote absorption of proteins
   • Decreased risk of poor structural formation of collagen (scar tissue)
2. Pain and Nerve Conduction:
   • Ultrasound selectively heats peripheral nerves, and alters or blocks impulse conduction and increases membrane permeability.
   • May block pain mechanism through effecting nerve.
3. Circulation:
   • Improved local circulation.

This heating effect occurs when the ultrasound is set on continuous. This means that the ultrasound is on 100% of the time. For non-thermal effects, one should be aware of the duty cycle. This represents the on and off time of the ultrasound. In the case of pulsed ultrasound, the duty cycle may be 20%, 40%, 50%, etc. In the case of 20% duty cycle, the ultrasound is only on 20% of the time. For acute injuries, the setting should be 20-50%. For subacute injuries, the duty cycle should be 50-80% to aid in the change-over to heating modalities.

For both thermal and non-thermal ultrasound, the following are appropriate intensities: acute - .1-.5 watts/cm2, subacute - .5-1.0 watts/cm2, chronic - 1.0-1.5 watts/cm2. All treatments should last 5 minutes.

When applying therapeutic ultrasound, a transmission gel should be used to produce better conductivity. It is important to use a small, circular pattern while keeping the ultrasound head in constant contact with the area. This maintains a high coupling effect, which will allow the patient to receive the greatest benefits.

Ultrasound can also be transmitted through water in cases where the area being treated is irregular in shape or the faceplate is too large to accomodate the area. The athlete sticks the area in a bucket of water while the athletic trainer administering the ultrasound holds the faceplate just under the surface of the water, 2 inches above the area being treated. An important point to keep in mind is that 60% of the ultrasound intensity is lost through water. So the intensity level needs to be increased to accomodate for this.

When turning the ultrasound on, the ultrasound head must be kept in contact with the gel or water. This helps prevent the crystals inside the head from shattering.