What is time gain compensation in ultrasound?

Answer 1

Ultrasound attenuates as it propagates through the body. When used to image the biological tissues, the echo signals need to be progressively amplified to allow the visualization of the shallow regions simultaneously with the deeper regions. Time Gain Compensation, or TGC, is that amplification step. The amplification coefficient, or gain, needs to increase with depth, as the signal gets smaller and smaller. But in ultrasound imaging, the speed of sound is usually assumed to be constant, creating a direct equivalence between distance and time, which is why the compensation of the gain is implicitly said to change with time, hence the name.