Knobology: the four knobs that matter

Machines have dozens of buttons; four matter on almost every scan. Turn them below.

Live simulator — try itFull interactive lesson →

Depth

Start deep to survey, then bring the target to the middle of the screen with a little room behind it.

Gain

Overall brightness. Fluid should be black and solid organs mid-grey. Too much gain fills fluid with fake echoes — the classic reason free fluid gets missed.

Focus

The depth where the beam is narrowest. Place it at or just below what you care about.

Frequency

The highest frequency that still reaches the target: higher is sharper, lower is deeper.

Real scans

Normal gallbladder — A thin-walled, black (fluid-filled) gallbladder within the liver, with no stones. — **Normal gallbladder.** A thin-walled, black (fluid-filled) gallbladder within the liver, with no stones. Nevit Dilmen · CC BY-SA 3.0 · source

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FAQ

What is TGC?

Time-gain compensation amplifies later (deeper) echoes so the image is even from top to bottom.

Related guides

Linear, curvilinear or phased array?The three ultrasound probes explained — frequencies, footprints, image shapes and which to use for vessels, lungs, abdomen and heart — plus the probe marker convention.
Ultrasound artifacts, explainedAcoustic shadowing, posterior enhancement, reverberation (A-lines), B-lines, mirror image and edge artifacts — why they happen and how they help diagnosis.
Gallstones and cholecystitis on ultrasoundWhat gallstones look like on ultrasound (bright, shadowing, mobile), the signs of acute cholecystitis, and how to find the gallbladder. Interactive simulator and real scans.

Educational content for learners; follow local protocols and supervision. Simulated images are generated by Sonoduck’s physics model; real images are credited individually.