Final answer:
In ultrasound imaging, the 'beam-steering gradient' is utilized for the precise control of the direction of the emitted ultrasound waves during the sampling or production of an echo.
Step-by-step explanation:
The gradient that is on during the sampling or production of an echo in ultrasound imaging is referred to as the beam-steering gradient. During the ultrasound imaging process, a speaker-microphone broadcasts a directional beam, sweeping this beam across the area of interest to produce images like those in various figures described in your material. This directional beam is created by phasing multiple ultrasound sources in the probe's head to interfere constructively. Additionally, echoes are measured as a function of position and depth, allowing a computer to construct an image that reveals the shape and density of internal structures. The beam-steering gradient is an integral part of this process, enabling precise control over the direction of the emitted ultrasound waves.