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.

From SIUI Inc.;
'The CTS-285 is designed for the diagnosis of liver, gallbladder, kidney, pancreas, thyroid, breast, uterus, bladder, ovary, etc. It is a portable versatile ultrasound scanner with convex and linear array scanning.'

From SIUI Inc.;
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From SIUI Inc.;
'Incorporating the latest advances in technology, the CTS-6000 digital B/W ultrasound system provides exceptional imaging quality and complete diagnostic capabilities. It is equipped with extensive analysis package, super broadband multifrequency probes and disk storage capacity, a complete system that fully meets different clinical needs.
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To calculate the echo position, a constant sound speed of 1538.5 m/sec is assumed. Tissue penetration is frequency depended, if the frequency increases, the imaging depth decreases. The range resolution defines the depth. Ultrasound propagating in tissue is attenuated due to scattering and absorption. The attenuation is proportional to depth and frequency and is typically in the range from 0.5 to 1 dB/(MHz cm).

See also Attenuation Coefficient, Proximity Sensor, and Echo Ranging.