Time gain compensation in orbital ultrasonography

Abstract

Time gain compensation (TGC) is a setting applied in diagnostic ultrasound imaging to account for tissue attenuation. By increasing the received signal intensity with depth, the artifacts in the uniformity of a B-mode image intensity are reduced. The purpose of TGC is to normalize the signal amplitude with time, compensating for depth. When the image is displayed, similar materials should have similar brightness, regardless of depth; this is achieved by “Linear-in-dB” Gain, which means the decibel gain is a linear function of the control voltage. Gain is expressed in dB, a logarithmic ratio of the output power relative to the input power. Gain can be calculated by subtracting the input from the output levels when both are expressed in dBm, which is power relative to 1 milliwatt. The TGC creates uniformity in the brightness of the echoes when used in conjunction with the overall gain. The best approach is to center all the TGC settings before adjusting the overall gain. After adjusting the overall gain, the TGC can then be adjusted to compensate for attenuation at specific depth. Gain is a uniform amplification of the ultrasonic signal that returns to the transducer after it travels through the tissue.