Echocardiographic Imaging Techniques and Instrumentation
Image optimization
Transducer selection balances penetration and resolution. Neonates and infants tolerate higher-frequency probes, often 7–12 MHz, while older children and adults require lower frequencies. Harmonic imaging improves endocardial border detection but can reduce frame rate. Frame rate depends on depth, sector width, and color box size. A large color box or excessive depth lowers frame rate and can make jets appear falsely broad. Adjust color gain until flow is visible without speckle, and set the color scale just above the expected peak velocity to avoid aliasing.
Doppler principles
Pulsed-wave Doppler is range-specific and best for low-velocity flow. Continuous-wave Doppler is not range-specific and is required for high-velocity jets. The Nyquist limit equals half the pulse repetition frequency; when velocity exceeds it, aliasing occurs. Keep the Doppler angle within 20 degrees, ideally less than 15 degrees, and use angle correction when appropriate. Wall filters remove low-velocity clutter but can erase low-flow signals. Transesophageal and three-dimensional echocardiography add complementary views when transthoracic windows are limited.
Traps
Using pulsed-wave Doppler for a 5 m/s jet causes aliasing and underestimation. Measuring a gradient without aligning the cursor to flow underestimates the true velocity. Excessive color gain creates false jets, while too low a scale hides true jets.
Rule of thumb
Set the color or spectral scale just above the expected peak velocity, and use continuous-wave Doppler for any jet that aliases or exceeds about 2 m/s.
Worked example
A ventricular septal defect jet aliases at 2 m/s with pulsed-wave Doppler. Switch to continuous-wave Doppler, align the cursor with the jet, and measure a peak of 4 m/s. The simplified Bernoulli gradient is 4V², or 64 mm Hg.