Color and Spectral Doppler

• Color box: set the 2D sector and the color box as narrow and shallow as possible while covering all the flow of interest; this maximizes frame rate and velocity scale.
• Color gain: raise it until random speckle appears outside the flow, then lower it until the speckle just disappears. Readjust often during the study.
• Color scale: default Nyquist 50 to 70 cm/s in each direction for routine color and regurgitant jets. The same jet looks larger at a lower scale. Use about 30 cm/s for low-flow regions (atria, pulmonary veins). Record blood pressure, since driving pressure also changes jet size.
• Color map: red toward, blue away, black at zero; brighter hues are faster. Laminar flow is a pure color, turbulence a mosaic; variance maps add green and yellow.
• Spectral scale and baseline: display the signal as large as possible without aliasing, but do not cut off flow in the opposite direction.
• Sweep speed: 100 mm/s for all velocity and time measurements (VTI, slopes, intervals); 25 mm/s to show respiratory variation over many beats.
• Sample volume: 1 to 3 mm at the tips of the open mitral or tricuspid leaflets (mitral gate toward the lateral wall); about 3 to 5 mm in the LVOT, centered about 5 mm proximal to the aortic valve. Too large a sample volume causes spectral broadening; too close to the aortic valve broadens the LVOT signal.
• Wall filter: removes high-intensity, low-velocity clutter from walls and leaflets. Set it so the beginning and end of flow are clearly shown; lower it for low velocities, raise it for high velocities.
• Gain: show the full spectrum of velocities without noise. Measure the modal velocity (densest part) for laminar flow, or the distinct outer border for turbulent flow.
• Angle: keep the beam parallel to flow. A 20° angle reduces the measured velocity by only 6%. Angle correction is not recommended in echocardiography; use several views instead and report the highest good-quality signal.
• PW, HPRF and CW: PW gives depth-specific velocity but aliases above the Nyquist limit; HPRF adds sample volumes to raise the limit at the cost of range ambiguity; CW has no Nyquist limit but no depth resolution.
• Mitral inflow: record E, A and deceleration time. With tachycardia, E and A can fuse; do not measure DT if A starts on the E slope above 20 cm/s.

Mitchell C, Rahko PS, Blauwet LA, et al. Guidelines for performing a comprehensive transthoracic echocardiographic examination in adults: recommendations from the American Society of Echocardiography. J Am Soc Echocardiogr. 2019;32(1):1-64.

• Doppler only measures the part of the blood velocity that runs along the ultrasound beam. Flow toward the transducer is shown red on color and above the baseline on spectral; flow away is blue and below the baseline (BART: blue away, red toward).
• The color bar is a velocity map. The black band in the middle is no detectable shift (removed by the wall filter); brighter colors are faster. The number at each end is the Nyquist limit.
• Aliasing: when blood moves faster than the Nyquist limit, the color wraps to the opposite color and the PW spectrum wraps around the scale. Lower the depth, raise the scale, shift the baseline, or switch to CW.
• PW samples one small gate, so you know where the velocity came from, but its maximum measurable velocity is limited by depth. CW listens along the whole line, so it can record high velocities (like TR) but cannot tell you where along the line they came from.
• Angle matters: the measured velocity equals true velocity × cos θ. At 20° the error is about 6%; at 60° the machine reads only half the true velocity. Align the beam with the jet.
• LVOT VTI is the area under the LVOT PW envelope (the distance blood travels per beat). Stroke volume = VTI × LVOT area. Normal VTI is about 18 to 22 cm; a low VTI suggests low stroke volume.
• Doppler sound: the pitch rises with velocity. Laminar flow sounds like a clean whoosh; turbulent jets sound harsh. Flow toward the probe plays in the right ear and flow away in the left.
• Peak TR velocity estimates RV systolic pressure with the simplified Bernoulli equation: RVSP ≈ 4v² + RA pressure.