reciever functions

Order of 5 receiver functions?

Amplification > compensation > compression > demodulation > reject

What amplification ( gain ) does ?

• Brightens the entire image equally

• Aka: overall gain / receiver gain

• User controlled

• Does not improve signal-to-noise ratio

Compensation ( TGC )

Fixes attenuation w depth

Compression

Changes contrast / number of gray shades

Demodulation

Rectification + smoothing ( not operator controlled )

Reject

Removes low level noise

What is reject (threshold)?

• Eliminates low-level echoes / noise

• Only affects darkest echoes

• User controlled

• Too high → loss of weak structures

What is demodulation?

• Converts RF signal to video form

• 2 steps: rectification + smoothing (envelope detection)

• Not user controlled

• Does not change image appeara

What does compression (dynamic range) do?

• Reduces wide range of echo amplitudes to fit display

• Changes contrast (soft vs hard image)

• User controlled

• Keeps signal within display range

What does TGC (Compensation) do?

• Corrects for depth-dependent attenuation

• Makes image uniformly bright from near → far

• User controlled

• TGC curve: near, mid, far zones

What does the receiver do? (List the 5 receiver functions)

1. Amplification (Gain) – boosts all echoes

2. Compensation (TGC) – boosts deeper echoes

3. Compression – squeezes signal into a range the monitor can show

4. Demodulation – makes the signal into a smooth wave

5. Reject – removes low-level noise speckles

What is dynamic range?

Dynamic range = how many shades of gray the system displays.

-High dynamic range = more grays (soft, more shades)

-Low dynamic range = fewer grays (more black/white contrast)

What is TGC (Time Gain Compensation)?

TGC adds more gain to deeper echoes to make them the same brightness as shallow ones.

Because sound weakens as it travels, TGC brings up the deeper signals so the image looks uniform.

Think:

• Top of the sliders = near field

• Bottom = far field

What does the gain knob do?

Gain adjusts the overall brightness of the entire image equally.

• It amplifies all echoes exactly the same amount.

• It does not change how deep sound travels.

• It does not change patient exposure.

What is amplification?

Amplification = the process of increasing the strength (size) of the returning echoes.

• Yes, it’s what the gain knob controls.

• Gain does NOT add energy to the body, it only makes the returning signal brighter after it comes back.

• More gain = brighter image

• Less gain = darker image

What is compression?

Compression reduces the range of signal intensities so they can fit on screen.

• It changes contrast

• Higher compression = more grays

• Lower compression = more black & white

What is demodulation?

Demodulation changes the echo signal from a messy wave to a smooth one so the system can display it.

Two steps:

• Rectification (makes all waves positive)

• Smoothing / Enveloping

You don’t adjust this — it’s automatic.

What is reject?

Reject eliminates low-level noise so black areas look cleaner.

• Too much reject = you erase weak real echoes

• Too little = speckly image

What is overall depth used for?

Depth sets how deep the system sends sound and how deep the screen displays echoes.

• More depth = smaller structures

• Less depth = bigger structures

What is focal zone?

Focal zone = the point where resolution is best (beam is narrowest).

Bottom line:

• Put the focal zone at or just below the structure you want to see clearly.