When stenosis is minimal, the flow through the vessel stays largely laminar, with only a small acceleration through the narrowed segment. This produces only a tiny spread of velocities within the sample volume, seen on the Doppler spectrum as minimal spectral broadening. As stenosis worsens, turbulence increases and spectral broadening becomes moderate to severe. No spectral broadening would imply an almost perfectly mono-velocity flow, which is not typical even with minimal narrowing. Therefore, the best description for minimal stenosis is minimal spectral broadening.

Collateral flow through the circle of Willis can compensate when one ICA is stenosed, so the brain relies on the opposite side to supply blood. On Doppler, this shows up as higher flow volumes and velocities in both carotid systems because more blood is being delivered through shared pathways to the affected hemisphere. The key clue is that the spectra would be smooth and laminar, without the turbulent jet that comes from a locally significant stenosis. So seeing increased flow in both ICAs and CCAs with no turbulence points to redistribution of flow via collateral pathways rather than a single artery with a high-grade stenosis causing a turbulent jet. If flow were increased only on the contralateral side with turbulence, that would suggest a focal stenotic jet rather than collateral compensation. Normal flow on both sides or decreased contralateral flow would not reflect active collateral redistribution.

Decibels express ratios on a log scale, and for power the formula is dB = 10 log10(P2/P1). If power is reduced by a factor of 100, P2/P1 = 1/100. So dB = 10 log10(1/100) = 10 × (-2) = -20 dB. The negative sign simply indicates attenuation. In words: a 100× reduction in power corresponds to a 20 dB drop.

In ICA stenosis, the brain can recruit collateral pathways from the external carotid artery to perfuse intracranial vessels. When the ECA becomes a major source of intracranial flow, it is effectively internalized, and most of its flow is directed into intracranial collaterals rather than distally through the ECA branches. On Doppler, this redistribution often results in little or no detectable forward flow in the ECA itself, appearing as flow ceasing. This pattern reflects collateral circulation taking over the intracranial supply rather than a normal or occlusive pattern of the ECA.