THERAPEUTIC ULTRASOUND





DEEP HEATER AND OTHER MECHANICAL EFFECTS



Therapeutic ultrasound is a mechanical pressure wave applied to tissues at a level of intensity that is so low and at a frequency that is so rapid, the pressure itself cannot be detected by the person receiving it. Ultrasound treatment streams of pressure waves are transmitted to a small volume of tissue, which causes the molecules of the tissue to vibrate.





Ultrasound is considered a deep heater as its administration may result in increasing the temperature of tissues 3-5 centimeters below the level of the skin



Sound is a Form of Energy



Energy is a force that puts matter in motion. Energy does not have mass and does not take up space.


Sound energy travels in a sine wave form through air or other media and disrupts molecules in its path.


Sound waves do not carry heat, however its effects on media may produce heat.


Sound energy can be focused or collimated to give a greater directionality.










Ultrasound is generated by the process of conversion



High frequency alternating current s generated by the ultrasound machine.

The high frequency current is transmitted via a coaxial cable to the transducer.


The transducer head houses a piezoelectric crystal. When the electrical current is delivered to the crystal it causes the molecules of the crystal to be pushed together and pushed apart at high velocities.


Most ultrasound units are able to selectively generate sound wave frequencies a one or three mega hertz.

The molecular kinetic energy produces ultrasonic waves.

When the ultrasound waves are introduced to human tissue, depending on the tissue characteristics and tissue interfaces the energy is either reflected, refracted, absorbed.


When continuous streams of ultrasonic waves are absorbed by higher density tissue, the resultant increased molecular kinetic energy results in the development of metabolic heat.



Ultrasound can result in vigorous heating of deep tissue potentially heating selected tissues to up to 45 degrees celsius.


Refraction is a change in direction of wave energy when coming in contact to different media. For instance, when ultrasound energy reaches a tissue-air interface, it is refracted ninety degrees.

Reflection of ultrasound energy may result in destructive standing waves. Standing waves result when reflected waves are in phase with incoming waves. The intensity of these waves summate resulting in high amplitude, potentially destructive waves.


The formation of standing waves may be minimized by appropriately sizing the treatment area and continuously moving the transducer head during administration.




The common parameters of therapeutic ultrasound are selected based upon the therapeutic goals and pathological conditions



Intensity


A thin sheet of piezoelectrical crystal is firmly attached to the inner surface of the transducer head. Many ultrasound units provide two or three transducers with head diameter of 1-5 centimeters. The vibrating area of the crystal is typically slightly smaller than the diameter of the head. The area of the crystal producing the sound beam is called the effective radiating area (ERA). Intensity of ultrasound is determined by a ratio of total wats and ERA. Therefore therapeutic intensity range is 0.75 to 1.5 watts per cm^2.

Frequency


Frequency is the number of ultrasonic waves created per second and is measured in units known as hertz. Therapeutic ultrasound selectively generates frequencies at 1Mhz and 3.3 MHz. Frequency at 1Mhz yields deep penetration and 3.3Mhz less deep.

Mode

Ultrasonic energy may be delivered in a continuous or interrupted stream. Interrupted or pulsed ultrasound is use to minimize the heating effects of ultrasound while preserving non-thermal effects.


Treatment Area


The most effective size of an ultrasound treatment area is about twice the siz, and certainly no more than four times the size of the ERA.

Treatment Time


​Though there is no standard treatment time established, and research evidence is somewhat inconsistent, US treatment times are typically 5-10 minute

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All the general contraindications to therapeutic heat apply to ultrasound




Other Contraindications

Reproductive organs

Eyes

Anterior neck

Over implanted devices such as pacemakers, pumps, etc.




Precautions

Over plastic or cemented implants

Over active growth plate