Hemodynamic Disturbances in Posterior Circulation Stroke: 4D Flow Magnetic Resonance Imaging Added to Computed Tomography Angiography

Abstract

Objective: A clinically feasible, non-invasive method to quantify blood flow, hemodynamics, and collateral flow in the vertebrobasilar arterial tree is missing. The objective of this study was to evaluate the feasibility of quantifying blood flow and blood flow patterns using 4D flow magnetic resonance imaging (MRI) in consecutive patients after an ischemic stroke in the posterior circulation. We also explore if 4D-flow, analyzed in conjunction with computed tomography angiography (CTA), has potential as a diagnostic tool in posterior circulation stroke.Methods: Twenty-five patients (mean age 62 years; eight women) with acute ischemic stroke in the posterior circulation were investigated. At admission, all patients were examined with CTA followed by MRI (4D flow MRI and diffusion-weighted sequences) at median 4 days after the presenting event. Based on the classification of Caplan, patients were divided into proximal/middle (n = 16) and distal territory infarcts (n = 9). Absolute and relative blood flow rates were calculated for internal carotid arteries (ICA), vertebral arteries (VA), basilar artery (BA), posterior cerebral arteries (P1 and P2), and the posterior communicating arteries (Pcom). In a control group consisting of healthy elderly, the 90th and 10th percentiles of flow were calculated in order to define normal, increased, or decreased blood flow in each artery. “Major hemodynamic disturbance” was defined as low BA flow and either low P2 flow or high Pcom flow. Various minor hemodynamic disturbances were also defined. Blood flow rates were compared between groups. In addition, a comprehensive analysis of each patient’s blood flow profile was performed by assessing relative blood flow rates in each artery in conjunction with findings from CTA.Results: There was no difference in total cerebral blood flow between patients and controls [604 ± 117 ml/min vs. 587 ± 169 ml/min (mean ± SD), p = 0.39] or in total inflow to the posterior circulation (i.e., the sum of total VA and Pcom flows, 159 ± 63 ml/min vs. 164 ± 52 ml/min, p = 0.98). In individual arteries, there were no significant differences between patients and controls in absolute or relative flow. However, patients had larger interindividual relative flow variance in BA, P1, and P2 (p = 0.01, <0.01, and 0.02, respectively). Out of the 16 patients that had proximal/middle territory infarcts, nine had CTA findings in VA and/or BA generating five with major hemodynamic disturbance identified with 4D flow MRI. For those without CTA findings, seven had no or minor 4D flow MRI hemodynamic disturbance. Among nine patients with distal territory infarcts, one had major hemodynamic disturbances, while the remaining had minor disturbances.Conclusion: 4D flow MRI contributed to the identification of the patients who had major hemodynamic disturbances from the vascular pathologies revealed on CTA. We thus conclude that 4D flow MRI could add valuable hemodynamic information when used in conjunction with CTA.

Evaluating the Impact of Domain Boundaries on Hemodynamics in Intracranial Aneurysms within the Circle of Willis

“…When present, the BA supplies the posterior circulation of the brain without directly irrigating the anterior circulation. Therefore, the flux traversing the PCom is strictly unidirectional, carrying blood away from the ICA towards the PCA in accordance with the commonly observed flow direction [18,45]. According to our models, Patients B and C feed the distal PCA mostly (Patient C) or exclusively (Patient B) through the PCom due to their small or fetal P1 segments.…”

“…From an anatomical point of view, these vessels serve the purpose 50 of linking anterior and posterior circulations, thereby providing alternative pathways for 51 the blood in case of ischemia [17]. Frequently, the PCom carries a lesser net flow from the 52 ICA to the PCA, albeit different CoW configurations may perturb this rule [18][19][20]. The 53 majority of CFD studies that examine IA at the carotid arteries only consider one part of 54 the anterior circulation, thereby defining the PCom as a regular system outlet [15,21] or 55 neglecting it [22,23].…”

Hemodynamic Stroke: Emerging Concepts, Risk Estimation, and Treatment

“…Although this technology is promising, its implementation has thus far been limited by a long scan duration and the temporal and spatial resolution determining data quality need to be traded off against acquisition time. 50,53 Transcranial Duplex Sonography Ultrasound techniques support the evaluation of extraand intracranial cerebrovascular disease, including hemodynamic features, stroke cause, and risk prediction. Although neurosonology is highly operator-dependent, its advantages include safety, bedside availability, high temporal and spatial resolution, and cost-effectiveness.…”

“…Although this technology is promising, its implementation has thus far been limited by a long scan duration and the temporal and spatial resolution determining data quality need to be traded off against acquisition time. 50,53…”

Advances in differential diagnosis of cerebrovascular diseases in magnetic resonance imaging: a narrative review

“…It is a multi-modality approach using phase-contrast MRI to enhance assessments of blood flow and hemodynamic analysis in cerebral aneurysms and other CVDs. It uses a collection of high-resolution velocity fields to reconstruct the flow field (Figure 1H), which increases the spatial resolution and velocity accuracy in synthesizing MRI data, and thus provides reliable evaluation of pressure and wall shear stress in cerebral aneurisms while providing volumetric and time-resolved visualization and quantification of blood flow (27,(40)(41)(42).…”