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.

(SA) The spatial average intensity is the acoustic power within the beam, divided by the beam area.

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

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

See also Thermal Effect, and Time Average Intensity.

The spatial resolution describes the smallest distance between two points in the object that can be distinguished as separate details in the image, generally indicated as a length or a number of black and white line pairs per mm (lp/mm). In ultrasound imaging, the spatial resolution means how closely two reflecting tissues - or scattering regions, can be to one another while they can be identified as different reflectors.