In addition, the amplitude attenuation coefficient of ultrasound is about 10–20 times higher in bone than in soft tissues. This causes the transmitted beam to be absorbed rapidly within the bone [17]. Ultrasound induces mechanical vibration of the particles or molecules of a material. Each particle moves small distances from its rest position but the vibrational energy is propagated as a wave traveling from particle to particle through the material. Ultrasound is attenuated as it travels through a tissue due to beam divergence, absorption, and deflection of

the acoustic energy. Deflection consists of the processes of reflection, refraction, and scattering. The energy required for a sound wave to travel through a tissue must overcome the internal Inhibitors,research,lifescience,medical friction Inhibitors,research,lifescience,medical intrinsic to any material. As a sound wave travels through tissue, it continually loses a proportion of its energy to the tissue (attenuation). The reasons of attenuation are divergence, deflection, and absorption. Divergence of the sound

beam spreads the acoustic energy over a larger Inhibitors,research,lifescience,medical beam area and reduces the intensity along the beam axis. Deflection of acoustic energy out of the beam also reduces the intensity. The greatest cause of attenuation in the body is absorption, in which energy is transferred from the sound beam to the tissue and ultimately is degraded to heat. The amount of absorption depends on the frequency of the ultrasound beam. Whenever a sound beam encounters a boundary between two materials, some of the energy is reflected and the remainder is transmitted through the boundary. The direction

of the reflected wave, or Inhibitors,research,lifescience,medical the echo, depends on the orientation of the boundary surface to the sound wave. The major physical effects of ultrasound are heat, mechanical effects, cavitation, and chemical effects. Acoustic impedance is a measure of the resistance that a material offers to the passage of Inhibitors,research,lifescience,medical an ultrasound wave and is expressed in units of rayls (kg/m2/sec). Acoustic impedance of water is 1.5 × 10−6 Mrayls whereas that of bone is 8 × 10−6 Mrayls. The greater the difference in acoustic impedance between two materials, the stronger Dacomitinib the echo (reflected wave) arising from their interface. Heat is the most common physical effect generated by sound waves in the body. When the rate of heat generation is higher than the rate of heat dissipation in the body, the body temperature will rise significantly. formerly Temperatures above 43°C if maintained for extended period can be damaging. Mechanical effects, such as the breaking of bonds, can occur if the amplitude of the ultrasound wave is significantly large. Cavitation occurs when an ultrasound beam of sufficient intensity travels through a liquid in which gas bubbles have been generated. The clearly alternating high- and low-pressure periods of the ultrasound wave forces the bubbles to contract and expand. The amplitude of the bubble oscillation increases with increasing ultrasonic intensity.