MR Derived Volumetric Flow Rate Waveforms at Locations within the Common Carotid, Internal Carotid, and Basilar Arteries

Abstract

The volumetric flow rate (VFR) waveform over the cardiac cycle in the cerebral vasculature is a significant factor in many studies, which involve cerebrovascular function. Perhaps contrary to expectation, the literature in this area is sparse and the characteristics of blood flow waveforms are ill defined. A better understanding of the variation of blood flow rate and pulsatility may aid our knowledge of risk factors involved in diseases and conditions, such as stroke, arteriovenous malformation, or aneurysm rupture. This study sought to characterise the blood flow waveform over the cardiac cycle at levels within the carotid artery and basilar artery (BA) in a normal cohort. The study cohort consisted of 22 subjects (recruitment age: 20 to 40 years) with no history of vascular disease (median age=26 years, interquartile range=25 to 32 years). Two-dimensional quantitative phase-contrast magnetic resonance imaging was performed on each subject at nine anatomic locations within the carotid artery and BA. Significant differences in pulsatility were present within the carotid tree. Archetypal VFR waveforms were established for this group at the nine locations. A normal individual's VFR waveform at a location within the carotid tree can be estimated by taking the group's archetypal waveform for that location, and scaling by the individual's average flow rate.

Dampening of Blood-Flow Pulsatility along the Carotid Siphon: Does Form Follow Function?

“…The discrepancy between the findings of Gwilliam et al 6 and our own results is most likely related to the underlying MR imaging technique for flow measurement. Along vessels without long straight sections, like the segments C3-C7 of the ICA, 2D PCMR with unidirectional velocity encoding can lead to an underestimation of peak flow values.…”

“…These limitations of 2D PCMR may explain the results of Gwilliam et al, 6 in which no significant reduction in pulsatility along the carotid siphon was found.…”

“…In contrast to 2D PCMR, this effect appears uniformly along the vessel independent of its geometric complexity. However, the study of Gwilliam et al 6 and ours are not fully comparable due to the different objectives and statistical approaches. In the present study, a general linear model was applied for a selective systematic comparison of pulse-wave characteristics at 2 locations.…”

“…25 In contrast, detailed assessment of hemodynamic parameters at different sites of the ICA has received relatively little attention so far. However, in a recent study, Gwilliam et al 6 assessed arterial pulsatility in a collection of healthy volunteers in the CCA and the ICA in both its proximal and distal course with 2D PCMR. A high reduction of pulsatility was found in the ICA immediately after the bifurcation compared with the CCA.…”

“…One publication, however, analyzed flow waveforms at different sites along the ICA to depict possible waveform changes. 6 In the present study, we applied flow-sensitive 4D PCMR imaging (time-resolved 3D PCMR) to assess carotid artery flow. In contrast to most 2D PCMR applications that use unidirectional velocity encoding, 4D PCMR allows velocity encoding multidirectionally in the acquired 3D data volume.…”