Time Gain Compensation: Adjusting Image Brightness at specific points within the image.
©Walter Rasmussen, R.D.C.S.
Time gain compensation (TGC) utilizes an array of sliding tabs which control the gain, (and therefore, image brightness), corresponding to specific depths, and is used to compensate for the decrease in the strength of the ultrasound returning from greater distances. The goal of TGC is to make the entire image look evenly lit from top to bottom.
The TGC Control Panel
In general use, the sliding tabs at shallower depths need to be adjusted closer to minimum gain, and gradually move toward maximum gain at greater depths, as in the illustration. If there is an isolated bright reflector, such as a prosthetic valve or calcification, the tab at the level of that bright reflector can be adjusted in order to see it more clearly. Adjusting an individual tab allows a higher level of attention to the quality of the image, involving more work however, the resultant diagnostic information is significantly improved.
Left: This image could have benefited from decreasing the near field Gain by sliding the TGC tabs for that area and revealing the structure that is obscured. A very bright area on the image also makes other areas more difficult to perceive.
return to HOME