Depth of penetration of the ultrasonic wave

Ultrasound is part of clinical practice since 1950 and remains a proven method of treatment for a range of clinical problems.

Ultrasonic energy

Ultrasound (US) is a form of energy, consisting of mechanical vibrations of varying frequency. Detectable by the human audible range is typically at a frequency of 25 to 20, 000 Hz. Sound above this frequency is called ultrasound. Frequencies used in medical physiotherapy is usually between 1.0 and 3.0 MHz (1MHz = 1 million cycles per second).

Penetration of ultrasonic energy is exponential in nature. More energy is absorbed in the surface layers than in the deep tissue, wherein the ultrasonic wave gradually weakens. In other words, there is no point at which energy is absorbed completely, but certainly has a point at which the levels of ultrasound energy levels are not sufficient to obtain a therapeutic effect. The deeper in the tissue penetrating ultrasound wave, the more energy will be absorbed and therefore has less energy to achieve the therapeutic effect at the end point. Amount of absorbed energy also depends on the type of fabric, as well as of ultrasound frequency. The lower the frequency, tolko deeper penetrating waves. The table below gives the average depth of penetration during treatment with ultrasound at a frequency of 1 MHz and at a frequency of 3 MHz.

Depth of penetration of the ultrasonic wave

Since it is difficult if not impossible to determine the exact thickness of each of these layers in different patients, so using averages for each of the most common frequencies used in physiotherapy:

1 MHz - 4.0 cm

3 MHz - 2.0 cm

To achieve a certain intensity ultrasound in depth should take into account the energy that has been absorbed by the tissues in the surface layers. The above table gives approximate reduction of the energy levels of typical tissue in two major frequencies used.

Since the penetration of the ultrasound is not uniform for each type of tissue, it is clear that certain tissues are capable of greater absorption of ultrasound by others. Typically, the tissues with high levels of protein will absorb more ultrasound energy, high water content absorbed less ultrasound energy (e.g., blood and fat). Tissues can be arranged according to their relative extent of absorption.

Blood - Fats - Nerves - Muscles - Skin - Tendon - Cartilage - Bone

More protein leads to greater absorption

Best absorption is in the joints, tendons and connective tissue

Although the cartilage and bone in the upper end of this scale, there is a problem with the reflection of the wave which means that the majority of US energy striking to the surface of each of these tissues do not absorb, but otrazvaa. Best absorbent tissue with respect to the clinical practice are those with a high content of collagen - joints, tendons, fascia (Syedinitelnotakanna skin which encloses the muscles and other organs), joint capsule, connective tissue.

The therapeutic application of ultrasound on tissue with a low level of energy absorption is less effective than the application of ultrasound energy to a highly absorbent fabric.