Brightening of echoes in the focal zone is a result of:

Brightening of echoes in the focal zone, often referred to as focal enhancement, occurs due to horizontal enhancement. This phenomenon involves the increase in echo amplitude as sound waves converge in the focal area of the beam, where constructive interference enhances the strength of the returning signals. As a result, structures located within this focal zone appear brighter on the ultrasound image because the intensity of the echoes is amplified.

In sonography, this effect is significant because it can help define structures with greater clarity in this area, but it may also lead to misinterpretation if not understood correctly. The increase in brightness is not due to actual changes in the tissue being imaged but rather a consequence of the ultrasound beam characteristics, primarily at the focal point where the beam is most concentrated. Understanding this concept is crucial for sonographers to accurately assess and analyze ultrasound images.

The other potential options do not correctly address why echoes appear brighter in the focal zone. For instance, acoustic speckle refers to the granular appearance of ultrasound images caused by interference of scattered echoes, and mirror image artifact involves the appearance of duplicate structures along a reflective surface. The term "Alice thickness artifact" pertains to inconsistencies in visualizing structures based on their thickness, which does not directly contribute to echo brightness