Final answer:
Adjusting the receiver gain in an ultrasound modifies the amplification, which is the process of increasing the signal strength to improve image quality.
Step-by-step explanation:
When the ultrasound user adjusts the receiver gain, they are modifying the amplification function of the system. In ultrasound imaging, amplification is the process of increasing the strength of the electrical signals that are received from the returning ultrasound waves after they have interacted with the tissues in the body. This makes the signals that represent different tissues or structures more distinct, thus improving the quality of the image. Correct adjustments to the gain can help in distinguishing between tissues of different densities and compositions.