Time Gain Compensation (TGC) is an electronic control that selectively amplifies echoes according to the time (and therefore depth) at which they return to the transducer. Because ultrasound attenuates as it travels through tissue, echoes from deeper structures are inherently weaker than those from shallow structures. TGC applies increasing amplification with increasing depth to produce a more uniform image. Most ultrasound machines allow manual TGC adjustment via a series of sliding controls corresponding to different depth zones.