Lateral resolution (ultrasound)
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Lateral resolution in ultrasound refers to the ability to discern two separate objects that are adjacent to each other. The ultrasound beam should be narrower than the gap between the two objects in order to resolve them 2,3.
At the focal region of the beam, lateral resolution is roughly three times worse than axial resolution in ultrasound, meanwhile, the axial resolution is about one wavelength in size 2.
The lateral resolution is primarily determined by the width of the ultrasound beam, which in turn is determined by the diameter of the transducer (or aperture diameter), amount of beam focusing, and number of lines per frame (or scan line density). The smaller the diameter of the transducer, the greater the beam focusing, and the greater the scan line density, the better the lateral resolution 2,3. The lateral resolution is also one-third of the diameter of the transducer 2. The beam focusing is only in the azimuthal plane 2.
Since greater focusing causes greater divergence of the beam beyond the focus region, setting multiple focal depths can help to improve lateral resolution beyond the focus region. The transducer is programmed to receive information from a certain focal depth at a time, and then the information from multiple focal depths is put together into a single frame 2,3. Thus, temporal resolution is reduced owing to the reduced frame rate 1.