What is the source of the bright echoes indicated by the arrow in this Doppler waveform?

• A. Aliasing
• B. Bruit
• C. Spectral broadening
• D. Mirror imaging

Answer: (B)

Noise in the Doppler signal causes those bright echoes; this is bruit, the random electronic/thermal noise present in the system. On a spectral display, brightness reflects signal amplitude at each velocity, so the random fluctuations from bruit show up as bright speckles across the spectrum that don’t correspond to actual blood flow. This is distinct from aliasing, which comes from too-low PRF causing a wrap of high-velocity signals; from spectral broadening, which reflects a real spread of velocities due to turbulence or multiple flow components; and from mirror imaging, which is a ghost of the spectrum across the baseline due to filtering artifacts. So the arrow points to bruit—the source of those non-physiologic bright echoes.