What does axial resolution indicate in ultrasound?

Axial resolution in ultrasound refers to the system's ability to distinguish between two closely spaced objects along the axis of the ultrasound beam. It is crucial for accurately identifying parallel reflectors, which are objects that lie in line with the direction of the ultrasound beam. High axial resolution allows for better visualization of distinct structures that are close together in the depth dimension, ensuring that they are represented clearly in the resulting image.

This capability is primarily determined by the spatial pulse length (SPL) of the ultrasound waves used during imaging; shorter pulse lengths result in better axial resolution. Therefore, when differentiating between closely spaced structures situated parallel to the beam, high axial resolution leads to clearer and more accurate delineation of these structures, allowing for better diagnostic accuracy.