Therapeutic Ultrasound

Definition

Ultrasound refers to sound waves with a frequency greater than 20,000 Hertz, which is above the range of human hearing. Therapeutic ultrasound is the application of sound waves to the human body to treat various medical conditions.

Purpose

Ultrasound can be used for a variety of therapeutic applications, including healing soft-tissue injuries and skin wounds, destroying tumors and calculi, and delivering medications. Ultrasound is the most commonly used therapeutic heat modality in sports medicine, and an emerging modality in minimally invasive surgery. Specific applications of therapeutic ultrasound include:

• healing musculoskeletal and soft-tissue injuries
• relieving joint pain associated with arthritis
• relieving chronic low back pain, and pain associated with plantar fascitis and bursitis
• stimulating bone fracture healing
• treating kidney stones, gallstones, and other calculi via extracorporeal shock wave lithotripsy (ESWL)
• enhancing the action of "clot-busting" drugs (thrombolysis) during treatment of stroke and heart attack
• halting internal bleeding associated with trauma (acoustic hemostasis)
• ablating cardiac tissue to treat arrhythmia
• destroying tissue to treat cancerous tumors, uterine fibroids, and benign prostatic hyperplasia (BPH).

Precautions

Therapeutic ultrasound should be delivered by a clinician trained and experienced in its use. Improper selection of treatment parameters may result in tissue damage. Its use may be contraindicated in pregnant patients, or for over the spine or brain.

Description

Therapeutic ultrasound typically uses sound waves in the range of 1 to 3 MegaHertz (MHz), or 1,000,000 to 3,000,000 vibrations per second. This mechanical energy is approximately 1,000 times that of the ultrasound energy commonly used for diagnostic imaging purposes. Lower frequencies are used for healing applications, while higher frequencies are used for deep heating and tissue destruction.

Low-frequency ultrasound stimulates healing by breaking up scar tissue and adhesions, improving blood flow, and reducing inflammation. High-frequency ultrasound, often referred to as high-intensity focused ultrasound (HIFU), causes the formation of tiny bubbles within tissue (cavitation) that vibrate and collapse, or induces coagulation of tissue and blood.

A therapeutic ultrasound system is generally portable or mobile, and consists of a control unit and a handheld probe with a crystal transducer through which sound waves are delivered through the patient's skin. In some ESWL systems, the patient is submerged in a water bath, and sound waves are delivered through the water. The clinician delivering the therapy selects the treatment parameters (e.g., intensity and duration). The patient usually experiences a comfortable feeling of heating or no sensation at all. The treatment time is 5-10 minutes, but may be longer depending on the condition being treated.

Recently, a focused ultrasound ablation system for use with magnetic resonance imaging (MRI) was introduced to non-invasively treat benign and cancerous tumors. This system is in development as a possible alternative to conventional surgery or radiation therapy.

Preparation

Therapeutic ultrasound for healing purposes, involves little patient preparation. A coupling gel is usually applied to the patient's skin to facilitate transmission of sound waves from the probe into the body. ESWL and HIFU procedures may require epidural or general anesthesia.

Aftercare

No aftercare is necessary for healing applications. HIFU and ESWL procedures involving anesthesia require that the patient recover in a post-anesthesia care unit.

Complications

Tissue damage may result from improper administration of therapeutic ultrasound. Complications related to anesthesia may occur following HIFU and ESWL procedures.

Results

The application of therapeutic ultrasound should result in relief of pain, faster healing, and/or resolution of the medical condition being treated.

Health care team roles

Therapeutic ultrasound for healing injuries or other rehabilitative/sports medicine applications is administered by a trained physical therapist or credentialed athletic trainer. Therapeutic ultrasound for healing chronic wounds is administered by a healthcare professional specializing in wound management and therapeutic wound healing modalities. For chronic pain applications, chiropractors, physical therapists, or pain management specialists may administer therapeutic ultrasound.

Specialists are usually involved in HIFU procedures. ESWL for kidney stones is generally performed by a urologist, and ESWL for gallstones by a gastroenterologist. A urologist also performs HIFU for prostate cancer and benign prostatic hyperplasia. HIFU for other cancer applications may be performed by an oncologist or surgeon with ultrasound training. HIFU for arrhythmia ablation is performed by an interventional cardiologist. Nursing staff are generally required for HIFU and ESWL procedures.

KEY TERMS

Ablation— Destruction of biological tissue by excision

Benign prostatic hyperplasia— A common condition that develops in older men involving enlargement of the prostate. It may be treated with high-intensity focused ultrasound.

Frequency— The number of sound wave vibrations per second. Typical ultrasound frequencies for therapeutic applications range from 1 to 3 MHz.

Magnetic resonance imaging— An imaging method that utilizes a magnetic field and computers to produce cross-sectional images of the anatomy.

Megahertz (MHz)— The measurement used to define the number of cycles per second of sound. One Hertz equals one cycle per second. One Megahertz equals one million cycles per second.

Thrombolysis— Dissolution or destruction of a blood clot using intravenous drugs or mechanical methods.

Resources

PERIODICALS

Cummings, Jennifer E., Antonio Pacifico, John L. Drago, et al. "Alternative Energy Sources for Ablation of Arrhythmias." Pacing and Clinical Electrophysiology. 28 (May 2005): 434-443.

Jolesz, FA, K. Hynynen, N. McDannold, and C. Tempany. "MR Imaging-Controlled Focused Ultrasound Ablation: A Noninvasive Image-Guided Surgery." Magnetic Resonance Imaging Clinics of North America. 13(August 2005) 545-560.

Ouellette, Jennifer. "New Ultrasound Therapies Emerge." The Industrial Physicist. American Institute of Physics. (September 1998): 30-33.

Uhlemann, C., B. Heinig, and U. Wollina. "Therapeutic Ultrasound in Lower Extremity Wound Management." International Journal of Lower Extremity Wounds. 2 (September 2003): 152-157.

ORGANIZATIONS

International Society for Therapeutic Ultrasound. http://www.istus.org/istu/index.asp.

American Physical Therapy Association. 1111 North Fairfax Street, Alexandria, VA 22314-1488. (800) 999-2782. Fax: (703) 684-7343. http://www.apta.org.

National Athletic Trainers' Association. 2952 Stemmons Freeway, Dallas, TX 75247. (214) 637-6282. Fax: (214) 637-2206. http://www.nata.org.

OTHER

Abella, H.A. "Focused Ultrasound Fries Pancreatic Cancer." Diagnostic Imaging Online. November 1, 2005. www.dimag.com/showNews.jhtml?articleID=172901932.

Klein, Milton J. "Deep Heat." eMedicine. December 12, 2001. http://www.emedicine.com/pmr/topic203.htm.