08 Ultrasound
Frame rate
FR = c / (2 d N_lines N_foci). Multi-focus and colour packets cost frames.
Listen
Listen · English
Simulation
Frame rate — Change the numbers; the scene follows.
Where it works
Ultrasound
Console
On the console — depth (13 µs/cm), PRF, frame rate, dynamic range, aliasing limit.
Open this machineFormula
Variables
Results
FR
Frame rate
50.13Hz
T_frame
Frame time
19.95ms
Curve
Explanation
What it means
Frame rate is limited by the speed of sound: each line needs a round trip, and multi-focus or colour packets multiply the lines. FR = c / (2 d N N_foci). Deep, wide, multi-focus colour is slow — that is why you drop lines or depth for cardiac rates. This is a working relation in Ultrasound.
Where it is used
Clinically it sits on the Ultrasound — Console. On the console — depth (13 µs/cm), PRF, frame rate, dynamic range, aliasing limit. Ultrasound equations sit on the probe face and along the beam: impedance, Snell, Doppler, MI and TI. They explain why gel matters, why aliasing appears, and why a mechanical index is on the screen.
Ultrasound · Open this machineHow to use it
128 lines, 12 cm, one focus → ~50 Hz. Two foci halve it. Parallel beamforming (modern boxes) can beat this formula. Change one input and watch the curve and the simulation follow.
Symbols
- dDepth12 cm
- N_linesLines per frame128
- N_fociFoci or packets1
- cSpeed of sound1,540 m/s
Worked example
A typical case from the default values: d = 12 cm (Depth); N_lines = 128 (Lines per frame); N_foci = 1 (Foci or packets); c = 1,540 m/s (Speed of sound). Substituting into the relation gives FR = 50.13 Hz; T_frame = 19.95 ms. These are teaching numbers — align them with your machine.
Typical values give
- FR = 50.13Hz
- T_frame = 19.95ms
Where it comes from
The displayed formula is the working relation. FR = c / (2 d N_lines N_foci). Multi-focus and colour packets cost frames. Usual reference: Bushberg. Derive it in the specialty lesson, then return here to pin the numbers.
Reference: Bushberg
Assumptions & limits
One beam at a time, no multiline acquire. Sector vs linear line density is your N. Dead time between frames is omitted.
Pitfalls
Soft-tissue 1540 m/s is an assumption — not a measurement in that patient. Doppler angle 90° gives no shift. MI and TI are on-screen estimates, not absorbed dose. One beam at a time, no multiline acquire. Sector vs linear line density is your N. Dead time between frames is omitted.
Keep this
Gel, angle, and assumed speed of sound — get those three right before you trust a centimetre. One beam at a time, no multiline acquire. Sector vs linear line density is your N. Dead time between frames is omitted.
In this specialty