Therapeutic ultrasound applications

Ultrasound is acoustic (sound) energy in the form of waves that have a frequency above the human hearing range. The highest frequency that the human ear can detect is approximately 20 thousand cycles per second (20,000 Hz). This is where the sonic range ends, and where the ultrasonic range begins. Ultrasound has many uses and is commonly used in electronic, navigational, industrial, and security applications. It is also used in medicine to view internal organs of the body.

Within the medical framework ultrasound can be sued for both Medical Imaging and Therapeutic treatment.

In ultrasonic medical imaging, high-frequency acoustic energy is transmitted into the human body using a set of transducers directly attached to the skin. Gel is used on all surfaces of the head to reduce friction and assist transmission of the ultrasonic waves. The ultrasound waves reflect from boundaries between organs and surrounding fluid, and between regions of differing tissue density.

Therapeutic ultrasound refers generally to any type of procedure that uses ultrasound for therapeutic benefit. This includes HIFU, lithotripsy, targeted ultrasound drug delivery, trans-dermal ultrasound drug delivery, ultrasound hemostasis, and ultrasound assisted thrombolysis

The origins of therapeutic ultrasound have,as is most common in the intial period of discovery of many techonological advancements, a Military origin. It was discoverd during the first large scale application of ultrasound in World War II that the Sonar systems used to navigate submarines were heating and killing fish at ultrasonic frequencies. This led to research in the ultrasound properties of tissue heating and healing effects.

The therapeutic ultrasound frequency used is typically 0.7 to 3.3 MHz. Maximum energy absorption in soft tissue occurs from 2 to 5 cm. Intensity decreases as the waves penetrate deeper. They are absorbed primarily by connective tissue: ligaments, tendons, and fascia (and also by scar tissue).

There are three primary benefits to ultrasound. The first is the speeding up of the healing process from the increase in blood flow in the treated area. The second is the decrease in pain from the reduction of swelling and edema. The third is the gentle massage of muscles tendons and/ or ligaments in the treated area because no strain is added and any scar tissue is softened. These three benefits are achieved by two main effects of therapeutic ultrasound.The two types of effects are: thermal and non thermal effects. Thermal effects are due to the absorption of the sound waves. Non thermal effects are from the vibration of the tissue causing microscopic air bubbles to form, which transmit the vibrations in a way that directly stimulates cell membranes. This physical stimulation appears to enhance the cell-repair effects of the inflammatory response.

Applications:

Lithotripsy, focused high-energy ultrasound pulses can be used to break calculi such as kidney stones and gallstones into fragments small enough to be passed from the body without undue difficulty.

Phacoemulsification - This is the use of Ultrasound in modern cataract removal in the eye. Using an instrument called a Phaco probe which is an ultrasonic handpiece that has a titanium or steel needle. In this procedure the surgeon gains acces to the lens using standard surginal cutters and then the The tip of the needle of the probe vibrates at ultrasonic frequency to sculpt and emulsify the cataract while the pump aspirates particles through the tip. The result is that the cataract is usually broken into two or four pieces and each piece is emulsified and aspirated out with suction pump.

Acoustic targeted drug delivery. This is a method that uses ultrasound energy to enhance the transport of molecules into and/or across specific tissues. The ultrasound source is pulsed on and off, and moved in a defined pattern to sonicate the tissue of interest. The pulsing of the ultrasound serves two purposes 1. to agitate the tissue matrix by extending and compressing it, and 2. to keep the tissue from absorbing to much energy and ablating it (or causing necrosis). This makes the cell membrane more permeable to pharmaceutical agents.The same principle can also be applied to creating more populated laboratory cultrues of microorganisms by increasing uptake of nutrients.

Removal of cancerous tumors. In a process called MRGFUS which stands for Magnetic resonance imaging focused ultrasound surgery. The ultrasound waves are used to destroy cancerous tumors under the guidance of MRI. Treatment of varicose viens- During Endovenous laser treatment - where an optical fibre utilizing IR light which causes the vessel to contract is guided to the affected vessel under the direction of ultrasound. Destruction of bacteria by acting synergistically with antibiotics. Tissue and bone regeneration. Dental Hygiene.

Sources:

Therapeutic Ultrasound in Physical Therapy - http://automailer.com/tws/ultrasound.html Halliday,D. Resnick,R. et al... Fundamentals of Physics,7th ED 2004, John Wiley and Sons Ultrasound Medline Plus- http://www.nlm.nih.gov/medlineplus/ency/article/003336.htm Ultrasound (sonography)- http://www.radiologyinfo.org/en/info.cfm?pg=genus Ultrasound therapy- http://www.mayoclinic.com/health/ultrasound/MY00308