IMG-31

Ultrasound round-trip attenuation

A_dB = 2 α f z. Soft-tissue α ≈ 0.5 dB cm⁻¹ MHz⁻¹.

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UltrasoundUS attenuation

Governing equation

A_{\mathrm{dB}}=2\alpha f z

where

\alpha: Attenuation α (dB/cm/MHz)
f: Frequency (MHz)
z: Depth (cm)
A: Round-trip loss (dB)

Lecture brief

Historical brief

Larmor precession, CT Beer projections, SNR and Nyquist sampling are why MRI and CT images exist as numbers. The lab computes frequency, dose and resolution limits. This sheet (IMG-31 — Ultrasound round-trip attenuation) is the form associated with US attenuation. Working symbols: $\alpha$ , $f$ , $z$ $\rightarrow$ $A$ . TGC restores the depth-dependent loss. Bone and air stop the beam (α huge, Z mismatch).

Purpose

Purpose: compute

A

from

\alpha

f

z

in Medical imaging via

A_{\mathrm{dB}}=2\alpha f z

A_dB = 2 α f z. Soft-tissue α ≈ 0.5 dB cm⁻¹ MHz⁻¹. Use it when a real medical imaging question must be answered in SI before a code check.

Live realistic example

In symbols

Live case. Given

\alpha = 0.500\,\mathrm{dB/cm/MHz}

f = 5.000\,\mathrm{MHz}

z = 6.000\,\mathrm{cm}

, the governing relation

A_{\mathrm{dB}}=2\alpha f z

yields

A = 30.00\,\mathrm{dB}

. A fading echo from deeper tissue. Move a slider: the numbers are this situation, not a canned story.

Calculator

Inputs

Attenuation α \alpha0.5 dB/cm/MHzFrequency f5 MHzDepth z6 cm

Outputs

Round-trip loss A30.00 dB

Reading speed

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Narration of this film

A fading echo from deeper tissue.

TGC restores the depth-dependent loss. Bone and air stop the beam (α huge, Z mismatch).

Reading speed

Watch on YouTube