Why do you place the focal zone just under the structure you want to see?

The focal zone marks the depth where the ultrasound beam is most tightly focused, which improves lateral resolution and sharpens fine detail. Placing it just under the structure you’re evaluating gives the beam room to converge so the image looks clearest at the level you care about. A quick way to do this is to find the small focus marker on the depth scale and slide it so it sits just below your target.

If the focal zone sits too high, the area above your structure may look sharp while the structure itself looks slightly blurred. If it’s set too low, the beam has already spread out again, which reduces clarity.

A simple example is the supraspinatus tendon. If the focal zone is too shallow, the tendon can look a little soft or hazy. Moving the focal zone just below the tendon sharpens the tendon fibers and the bony surface of the greater tuberosity.