(I) The intensity of a wave is the rate of power through a unit region perpendicular to the direction of propagation. The unit of intensity is watts per square meter (W/cm2).

(SP) The spatial peak intensity is the point in the sound field with maximum intensity.

(ITA) The time average intensity is the average ultrasound intensity calculated over the time between pulses.
Time average intensity = Pulse average intensity x Duty factor
For ultrasound systems, the instantaneous intensity is averaged over one or more scan repetition periods for a specified scan mode.

(IPA) The pulse average intensity is the average intensity during the ultrasound pulse.

(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).