Biologic Effects and Safety:

Two bioeffects of ultrasound are heat and cavitation. As sound energy is transmitted through tissue, some energy is reflected and some energy is absorbed as heat. It has not been determined that medical ultrasound causes any deleterious effects. Cavitation is the formation, growth, and dynamic behavior of gas bubbles neither which have been determined harmful at the level of the medical usage. Mechanical effects of ultrasound include sheer forces and acoustic streaming.

AIUM Statements:

The American Institute of Ultrasound in Medicine states that as of 1982, no independently confirmed significant biologic effects had been observed in mammalian tissue below (medical usage) 100mW/cm2.

Measures of Intensity for Ultrasound:

Spatial Peak, Temporal Peak Intensity (SPTP) - the peak intensity at the point in space where the intensity is highest and that occurs when the ultrasonic emitting device is "on". It is highest of the measured intensities.

Spatial Average, Temporal Average Intensity (SATA) - the average power output of the device over the pulse repetition period divided by a reference, usually that of the transducer face. This measurement of intensity is the most quickly determined and most frequently quoted by manufacturers. It also yields the lowest more commonly used measures of intensity.

Spatial Average, Temporal Peak Intensity (SATP) - the peak intensity over a selected area, such as the transducer face, that occurs when the ultrasonic emitting device is "on."

Spatial Peak, Temporal Average Intensity (SPTA) - the maximal spatial intensity when the sound beam is "on" average over the pulse repetition period.

Spatial Peak Pulse Average Intensity (SPPA) - the pulse-averaged intensity measured at the point in space where the value is maximal.

Spatial Average Pulse Average (SAPA) - the pulse average intensity averaged over the beam cross sectional area.

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