(I-SPTA) Spatial peak time averaged intensity is the measure most associated with temperature rise.

See also Thermal Effect, and Time Average Intensity.

The thermal effect of ultrasound is caused by absorption of the ultrasound beam energy. As the ultrasound waves are absorbed, their energy is converted into heat. The higher the frequency, the greater the absorbed dose, converted to heat according the equation: f = 1/T where T is the period as in simple harmonic motion. Ultrasound is a mechanical energy in which a pressure wave travels through tissue. Heat is produced at the transducer surface and also tissue in the depth can be heated as ultrasound is absorbed.
The thermal effect is highest in tissue with a high absorption coefficient, particularly in bone, and is low where there is little absorption. The temperature rise is also dependent on the thermal characteristics of the tissue (conduction of heat and perfusion), the ultrasound intensity and the length of examination time. The intensity is also dependent on the power output and the position of the tissue in the beam profile. The intensity at a particular point can be changed by many of the operator controls, for example power output, mode (B-mode, color flow, spectral Doppler), scan depth, focus, zoom and area of color flow imaging. The transducer face and tissue in contact with the transducer can be heated.

See also Thermal Units Per Hour and Ultrasound Radiation Force.

Ultrasound therapy uses high energy sound waves to treat different diseases. Historically, the use of ultrasonic waves in therapy began before the wide use as a diagnostic medical imaging tool. Dependend on the intensity, ultrasound therapy reach from the thermal effect used in physical therapy to the destruction of tissue with lithotripsy.

Types of ultrasound treatment:
See also Thermal Index, History of Ultrasound, Interventional Ultrasound, and B-Mode Acquisition and Targeting.

This coefficient is a quantification of the energy intensity loss of waves (electromagnetic or mechanical) due to attenuation. In ultrasound imaging it is the relative energy intensity loss per traveled centimeter. The ultrasound attenuation coefficient is measured in units of dB/cm. The attenuation coefficient in soft tissues is nearly proportional to the ultrasound frequency. The attenuation coefficient is doubled when the frequency is doubled.
This coefficient (dB/cm) divided by the frequency (MHz) is almost constant in a given tissue.

Cross-section scattering is a measure of the scattering strength of a point scatterer. The scattering strength is dependent on the size of the scatterer, the density and compressibility of the scatterer and the surrounding medium, and the ultrasound wavelength.
If a transducer emits ultrasound with a total acoustic power of P, and the power is assumed to be uniform distributed over the US beam cross-sectional area, then the ultrasound intensity at a certain range, is defined by:
I = P/A
where I is the intensity, and A is the cross-sectional beam area at that range.
A point scatterer located in the ultrasound beam at this range, will scatter the ultrasound with a total acoustic power of Ps, defined by:
Ps = I s
where s is the scattering cross-section of the point scatterer.