The source level is the acoustic power (sound pressure) in decibels (dB) referenced to 1.0 microPascal measured at 1 meter from the sound source transmitted through a unit area in a specified direction.
The unit of intensity is watt per square meter, but source level is commonly given as a relative intensity in dB.

(AE) Induced acoustic emission is an effect of ultrasound contrast agents, presenting the interaction between the agent and the incident ultrasound wave.
Microbubbles break down in high-amplitude diagnostic ultrasound energy. The bubble rupture produces a transient pressure wave, which results in a characteristic mosaic pattern from tissues containing the agent. It is important to note that the color patterns of induced acoustic emission do not represent flow signals.

(ITP) The temporal (instantaneous) peak intensity is the maximum intensity during the ultrasound pulse.
The formula is: P2/rc
P is the instantaneous acoustic pressure, r is the density of the medium and c is the speed of sound in the medium.

See also Temporal Average Intensity (Time Average Intensity).

(IVUS) For intravascular ultrasound a small IVUS catheter with a probe is introduced into the artery. The transducer transmits and receives acoustic energy through this catheter. The reflected acoustic energy is used to build a picture of the inside of the vessel. A IVUS image consists of three layers around the lumen, the intima, media and adventitia.
In addition, elastography or palpography could be used to evaluate the local mechanical properties of tissues (e.g. lipid pools in high-risk vulnerable atherosclerotic plaques). These techniques use the deformation caused by the intraluminal pressure generated by the probe.
A high strain region at the lumen vessel wall boundary has 88% sensitivity and 89% specificity for identifying vulnerable plaques. There are high strain values of 1% in soft plaques with increased strain up to 2% at the shoulders of the plaque, while calcified material shows low strain values (0-0.2%). The radial strain in the tissue is obtained by cross-correlation techniques on the radio frequency signal. The strain is color-coded and plotted as a complimentary image to the intravascular ultrasound echogram.

See also Interventional Ultrasound, Vascular Ultrasound.

(LIPU / LIUS) Low intensity pulsed ultrasound is a form of mechanical power that is transmitted through and into tissues as an acoustic pressure wave. Low intensity pulsed ultrasound is often used in musculoskeletal and joint ultrasound and has therapeutic benefits for healing of (fresh) fractures, those that demonstrate either a delayed union or nonunion, and soft tissue repair.