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.

Also called B-mode echography, B-mode sonography, 2D-mode, and sonogram.
B-mode ultrasound (Brightness-mode) is the display of a 2D-map of B-mode data, currently the most common form of ultrasound imaging.
The development from A-mode to B-mode is that the ultrasound signal is used to produce various points whose brightness depends on the amplitude instead of the spiking vertical movements in the A-mode. Sweeping a narrow ultrasound beam through the area being examined while transmitting pulses and detecting echoes along closely spaced scan lines produces B-scan images. The vertical position of each bright dot is determined by the time delay from pulse transmission to return of the echo, and the horizontal position by the location of the receiving transducer element.
To generate a rapid series of individual 2D images that show motion, the ultrasound beam is swept repeatedly. The returning sound pulses in B-mode have different shades of darkness depending on their intensities. The varying shades of gray reflect variations in the texture of internal organs. This form of display (solid areas appear white and fluid areas appear black) is also called gray scale.

Different types of displayed B-mode images are:
The probe movement can be performed manual (compound and static B-scanner) or automatic (real-time scanner).
The image reconstruction can be parallel or sector type.

See also B-Scan, 4B-Mode, and Harmonic B-Mode Imaging.

The backscatter energy is the portion of the incident acoustic power scattered back toward the transducer.

The beam pattern shows the relative amplitude of the acoustic pressure as a function of direction relative to the transducer. Beam patterns are three-dimensional. The transmit and receive beam patterns are basically the same.

The width of the main beam lobe of the transducer is described in degrees. The beam width is usually defined as the width between the half power point and the -3dB point.