Ultrasound is a sound frequency greater than 20 kHz, which cannot be heard by the human ear. Therapeutic ultrasound is generally between 1 MHz (deeper) and 3.3 MHz (superficial) to penetrate into soft tissue depth of 1-5 cm.
How does it work?
Ultrasound passing through the tissue produces molecular motion and friction. This friction between particles can increase tissue temperature and cell activity.
The increased cell activity and tissue heating from the ultrasound can increase local blood flow, increase tissue extensibility, decrease edema/inflammation and muscle spasm, and increase enzymatic activity.
Additional effects of ultrasound
Movement of fluids along the acoustic boundaries as a result of the mechanical pressure wave associated with the US beam. This stimulus is perceived by the cells and amplified based on the cell size. Ultimately, cell plasma membrane permeability to calcium ions increase, allowing for increased cell activity and the synthesis and release of growth factors by macrophages.
This is the production and vibration of micron-sized gas bubbles in the coupling medium and fluid within the tissues. Gas bubbles move and compress in the tissue, causing increased cellular activity, resulting in a therapeutic healing process.
Ultrasound is applied to a patient through a transmission medium. Common transmission mediums are ultrasound gel, water, or lotion. Air is a poor transmitter of ultrasound, so the ultrasound head must maintain contact with the patient through the transmission medium. Ultrasound parameters include duty cycle (% of the time on), pulsed or continuous, intensity (amount of power per unit area), power (amount of acoustic energy per unit time, and frequency (number of cycles of ultrasound per unit time. Increasing frequency decreases the depth of penetration).
The area of treatment should be no more than twice the size of the ultrasound transducer head for maximal benefits. The transducer head is moved in a circular motion, or in a stroking motion. Holding the transducer head still over one area can rapidly increase the tissue temperature, so it is imperative to keep the ultrasound transducer moving.
- Over CNS tissues (brain and spinal cord)
- Over implants/prostheses
- Over pacemakers
- Over areas with thrombophlebitis, thrombus
- Reproductive organs
- Acute inflammation
- Growth plates
- Areas of fracture
- Over breast implants
- Over insensate areas