As the title asks: what are some artifacts caused by usage of time gain compensation (TGC).
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\$\begingroup\$ The title of a question posting is supposed to give us a sneak peek of what you're going to be asking, whereas the body is supposed to give us an insight of what you're doing and why you need to know what you asked. It's pointless if you all you ask is something that belongs in the title. \$\endgroup\$– user103380Apr 26, 2018 at 17:13
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\$\begingroup\$ Sorry I am new to US imaging and all I am asking is a question. System wouldn't let me post unless I write something in the body. Didn't know people would be this upset about this, should've asked somewhere else I guess. \$\endgroup\$– Stack_ProtégéApr 26, 2018 at 17:52
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Since path loss follows the inverse square law, B-Mode scanning for intensity vs density requires compensation with the speed of sound and time delay.
Displays for viewing are usually 8 bit per color or 256 level for monochrome the received signal must be compressed by time delay gain compensation that is performed by a quadratic ramp controlled gain starting very shortly after the transmitted burst,
Since the speed of sound in the fluid dielectric can vary slightly it is nominally set to 1.54 us/mm and the path depth includes the return or twice the depth , so this gain must increased by 12dB every unit of time delay. Since overall attenuation is also factored this quadration ratio has a gain constant with a slight focus variation for the propagation speed for maximum contrast. This implies that the Signal to Noise ratio drops 12db when distance is x2 or doubled, so it must be very high to reach maximum range.
Since the path loss is a combination of frequency sensitivity of reflection and absorption similar to the RF scattering parameters of s11 for Return Loss, the f may also be varied to optimize the Return Loss so get the highest Return loss which unlike 1 way radio waves, you want as much to reflect and return as possible while some variance dielectric like cysts may be more sensitive to absorption and thus appear black. Air gas on the interface must be avoided which cause higher false reflections or "birdies" as they called them on RADAR like a flock of birds near the antenna.
The frequency dependance on the body dielectric for sound is different than the speed of light which slows down with the square root of higher dielectric constant relative to air. Sound depends on physical density properties to propogate faster so imaging cannot be as high contrast as an optical camera signal without a lot of compensation for the medium.
