Dampening of blood-flow pulsatility along the carotid siphon: does form follow function?

BACKGROUND AND PURPOSE The tortuous distal part of the ICA may have an attenuating effect on pulsatile arterial flow. We investigated local arterial blood flow patterns in the ICA proximal and distal to the carotid siphon to detect quantitative waveform changes. MATERIALS AND METHODS Arterial flow patterns were analyzed by using flow-sensitized 4D PC MR imaging (time-resolved 3D PCMR) at 3T in 17 healthy volunteers. Time-resolved blood flow velocities were extracted from the source data at the C4 and C7 segments of the ICA. PI, RI, and PA were calculated by using time-resolved flow volume. A linear mixed-effects model was applied to compare values at C4 and C7. Furthermore, 3D blood flow visualization was performed for all 34 ICAs. RESULTS PI, RI, and PA were significantly lower at the distal C7 segment compared with the proximal C4 segment of the ICA (P < .0001). Helical flow patterns were observed in 5 ICAs of 4 subjects. CONCLUSIONS Arterial flow patterns showed a significant reduction in PI, RI, and PA when compared distal to proximal to the carotid siphon. The observed attenuation of flow pulsatility is most likely related to the contorted shape of the distal ICA and may bear a protective effect for downstream cerebral vasculature.