Diagram for calculating Pulsatility Index (PI).

A. Normal to mild SVD case: Initially, MCA was identified as identified as flow toward the probe from the temporal windows within an insonation depth of 50–60 mm. By slowly increasing insonation depth to 40 mm, bifurcation of the terminal internal carotid artery is identified. From this point, the entire length of M1 flow is evaluated until the signal is divided into two or three branches (M2 of MCA). Peak systolic velocity, end diastolic velocity, and mean flow velocity were obtained from proximal to distal M1 with 5 mm intervals of insonation depth. B. Severe SVD case: Patients with severe SVD have peaked shape waveforms, slight PSV reduction, and prominent EDV reduction. This results in increased PI value. C. PI was calculated as [PI = (peak systolic velocity–end diastolic velocity)/mean flow velocity].