What effect does increased focal depth have on ultrasound imaging?

Increased focal depth in ultrasound imaging affects axial resolution, which is the ability to distinguish between two structures that are parallel to the ultrasound beam. As the focal depth increases, the beam width also becomes wider, leading to a decrease in the ability to clearly differentiate between closely spaced objects along the axis of the sound beam. This results in a loss of detail in the image, particularly in the deeper structures being imaged.

In addition to this, other options, such as enhancing image brightness or improving contrast resolution, are related more to factors like gain settings and the processing algorithms used, rather than focal depth. Increasing the focal depth does not improve image detail, which is connected to resolution, but rather makes it more challenging to discern features distinctly. Thus, the correct understanding of the relationship between focal depth and axial resolution clarifies why an increase in focal depth leads to a decrease in axial resolution.