Fig. 1

(corresponding to b and c of Fig. 2 [1]). Note the different and confusing nomenclature regarding “mean velocities”. As depicted from the trace of the envelope of the Doppler spectra (yellow arrows), time-averaged maximum velocity is recorded, namely, TAV (time-averaged velocity) in (a) and TAP (time-averaged peak velocity) in (b). There is also no doubt in a that is TAP, because pulsatility index (PI) is calculated using this value [peak systolic velocity (PSV)-end-diastolic velocity (EDV)/TAV]. Time-averaged mean velocity is not recorded in (a), but is shown in (b) as TAM, traced in the middle of the Doppler spectra (white arrow). In TCCS, time-averaged maximum or peak velocities are the “mean” velocities that should be considered. The correct Lindegaard Index (Middle cerebral artery TAP/internal carotid artery TAP) in this case is 123/58, equal to 2.1 (corresponding to hyperemia if considered independently). It is thus clearly incorrect to use different “mean velocities” when calculating the LI, such as TAP/TAMEAN. Note: the waveform in (b) is consistent with an external carotid artery flow, given its sharp systolic upstroke, high-resistance velocity profile, and early diastolic notch (another mistake that should be taken into account)