The resolution is the ability to distinguish two adjacent objects or in Doppler measurements the smallest detectable change in flow. Probe resolutions are generally specified at 0.1Hz filtering.

See also Matrix Size.

Axial resolution is the minimum separation between two interfaces located in a direction parallel to the beam (objects above and below each other) so that they can be imaged as two different interfaces. The axial space resolution directly relates with the wave frequency, but higher frequencies have lower penetration into tissues.
The axial resolution is inversely proportional to the frequency of the transducer depending on the size of the patient. The higher the frequency the lower the axial resolution in large patients. This state results from the rapid absorption of the ultrasound energy with lower penetration. Lower frequencies are utilized to increase depth of penetration.

See also Damping.

The range resolution is the ability to determine the depth of reflectors.

Lateral resolution is the minimum separation of two interfaces aligned along a direction perpendicular (objects that are side by side) to the ultrasound beam. The lateral or angular resolution directly relates with the collimation of the beam emitted by the crystal. Lateral resolution is proportionally affected by the frequency, the higher the frequency the greater the lateral resolution.
Higher frequency transducers are used in fetal and pediatric echocardiography because the lateral resolution displays the smaller structures better. Lower frequencies are used for adults where structures are larger and the need for greater depth penetration is important.

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.