Today’s Quick Concept discusses transmit and receive gain. Throughout this series, I have tried to keep these videos very short, not exceeding 3-4 minutes. For this topic, to adequately explain the concept would require either a longer video, or subdivision into two parts. So this Quick Concept will actually be like one of those season ending cliffhangers.
Following Thanksgiving week, on December 3rd, we will release Transmit vs Receive Gain – Part 2.
TRANSMIT VERSUS RECEIVE GAIN – PART ONE
The first hurdle to clear in this discussion is that you will often encounter a wide range of words that describe the same principle during your studies on ultrasound. For those who tend toward literal memorization, this can be problematic. One familiar example of this is the multiple names for axial and lateral resolution. If you are not well aware that axial = longitudinal = radial = depth, or that lateral = azimuthal = transverse = width, the interchangeability of the terms will often be confusing.
In our discussion today, it should be noted that on the transmit side, increased gain = increased power = increased signal amplitude = increased voltage = stronger signal. So by manipulating transmit gain, you have a great deal of control over the signal that propagates into the patient.
Most beginning students would make an automatic assumption that ‘bigger is better’, but as you are familiarized with the concepts of attenuation, bioeffects, and the ALARA principle, that initial impression will change.
Whereas you can control the power of the signal transmitted into the patient, you cannot DIRECTLY affect how the signal reflects since the reflection is based primarily on the acoustic properties of the medium. However, indirectly, you can affect reflection by changing the scanning angle, the transmit frequency, the focus, and the view used. Changing the receiver gain does not affect the actual strength of the signal and hence will not necessarily result in better imaging. This relates to a concept called signal-to-noise, which we will be discussing in more depth later.
In the meantime, I hope you enjoy the holiday break and please join us on December 3rd for the conclusion of this discussion.
This subject matter is discussed more thoroughly in Frank Miele’s Ultrasound Physics and Instrumentation in Chapter 5: Transducers and Chapter 6: System Operation. Related discussions are in Chapter 3: Attenuation and Chapter 8: Artifacts.