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A 62-year-old woman with left internal carotid artery stenosis. Magnetic resonance angiography shows that the left internal carotid artery disappears (A). The vector map of time-resolved 3D phase-contrast (4D-Flow) MRI shows the antegrade flow of the affected-side the ophthalmic artery (OphA) (B). The rest and acetazolamide stress single photon emission computed tomography (SPECT) images show that cerebral blood flow and cerebral vascular reserve did not decrease in the territory of middle cerebral artery (MCA) (C).
Source publication
Background and purpose:
To assess the clinical feasibility of time-resolved three-dimensional phase contrast (4D Flow) magnetic resonance imaging (MRI) assessment of the ophthalmic artery (OphA) flow in patients with internal carotid artery stenosis (ICS).
Materials and methods:
Twenty-one consecutive patients with unilateral ICS were recruited....
Similar publications
Objective To assess the correlation between the angiographic appearance of cerebral collateral pathways or the degree of internal carotid artery stenosis (ICAS) and reduced cerebrovascular reactivity (CVR) estimated by single-photon emission computed tomography (SPECT) image analysis in patients with unilateral ICAS.
Methods A retrospective analysi...
Background:
Transcranial Doppler ultrasound remains the only imaging modality that is capable of real-time measurements of blood flow velocity and microembolic signals in the cerebral circulation. We here assessed the repeatability and reproducibility of transcranial Doppler ultrasound in healthy volunteers and patients with symptomatic carotid ar...
Citations
... Advancements in MRI technique and three-dimensional (3D) medical imaging workstation allow us to use 4D-flow MRI for clinical practice of several diseases [1][2][3][4][5] . A 4D-flow MRI is flow information in 3D space with a time axis, which consists of 3D morphological information and 3-directional phase imaging of flow information 6,7 . ...
Background and purpose: Carotid-cavernous fistulas (CCF), dural arteriovenous fistula (DAVF) and spinal arteriovenous fistula (SAVF) are rare vascular malformations that cause arteriovenous shunting. Detecting the shunt point and flow direction is necessary for shunt disease diagnosis and treatment. Hence, we propose a new shunt disease diagnostic way with four dimensional-flow magnetic resonance imaging (4D-flow MRI). Material and methods: The 4D-flow MRI and the DSA (digital subtraction angiography) were performed on 23 patients, including 2 with CCF, 20 with intracranial DAVF, and 1 with SAVF. Catheter embolization was performed in 19 patients. The 4D-flow MRI assessment was conducted for pre- and post-treatment (n = 9), pretreatment only (n = 12) and post-treatment only (n = 2). We use two functions of 4D-flow imaging application, one is a two-dimensional (2D)-colormap, which indicates velocity distribution with color scale for detecting shunt point, and another one is a 2D-flow vector for diagnosing flow direction.
Results: Shunt points are detected as red-colored lesions, with higher velocity compared with the surrounded area on 2D-colormap, with corresponding results to DSA findings. A 2D-flow vector indicates flow vectors of the main feeder, drainer, and influenced dural venous sinuses that could complement information obtained from other standard examinations. The post-therapeutic residual shunt flow analysis was consistent with DSA results except for one DAVF case.
Conclusion: 2D-colormap helps detect the shunt point of vascular malformations. A 2D- flow vector makes it possible to diagnose CCF, DAVF and SAVF based on flow dynamic analysis. A 4D-flow MRI would be an additional measurement for shunt disease diagnoses.
... Moreover, reversed OA flow has been associated with a 10-20% improvement in stroke outcome compared to patients with forward OA flow and the same degree of intracranial stenosis [155]. Analysis of OA flow direction may also help to predict intracranial hemodynamic impairment, since the ratio of cerebral blood flow at rest to normal control and cerebral vascular reserve is reduced in patients with non-native OA flow [156]. Diameter reduction and decreased blood flow velocities of the OA have shown strong associations with cerebral small vessel disease and the presence of cerebral microbleeds, enlarged perivascular spaces, lacunar infarcts and white matter hyperintensities. ...
Abnormal retrobulbar hemodynamics have been linked to the development of various ocular diseases, including glaucoma, age-related macular degeneration, and diabetic retinopathy. Additionally, altered retrobulbar blood flow has been observed in patients with severe cardiovascular diseases, including carotid artery occlusion, stroke, heart failure, and acute coronary syndrome. Due to the complex and intricate anatomy of retrobulbar blood vessels and their location behind the eyeball, measurement of retrobulbar blood flow and vascular reactivity, as well as the interpretation of the findings, are challenging. Various methods, such as color Doppler imaging, computed tomography angiography or magnetic resonance imaging, have been employed to assess retrobulbar blood flow velocities in vivo. Color Doppler imaging represents a fast and non-invasive method to measure retrobulbar blood flow velocities in vivo. While no information about vessel diameter can be gained performing this method, computed tomography angiography and magnetic resonance imaging provide information about vessel diameter and detailed information on the anatomical course. Additionally, ex vivo studies, such as myography, utilizing genetically modified animal models may provide high optical resolution for functional vascular investigations in these small vessels. To our best knowledge, this is the first review, presenting a detailed overview of methods aiming to evaluate retrobulbar blood flow and vascular reactivity in both humans and laboratory animals. Furthermore, we will summarize the disturbances observed in retrobulbar blood flow in retinal, optic nerve, and cardiovascular diseases.
... GT-Flow software, which was recently used to estimate the WSS of intracranial arteries and carotid artery, is well agreed with CFD, which is currently regarded as the gold standard for measuring cerebral hemodynamics. [15][16][17][18] A semiautomatic filter was applied to mask static tissue, including the brain parenchyma and skull. Two-dimensional analysis planes were positioned perpendicular to the long axis of the vessels in the M1 segment of the MCA. ...
... The WSS (maximum and mean) of the vessel through a cardiac cycle was measured as previous study. [17][18][19] ...
Background and purpose:
Various mechanisms are involved in the etiology of stroke caused by atherosclerosis of the middle cerebral artery (MCA). Here, we compared differences in plaque nature and hemodynamic parameters according to stroke mechanism in patients with MCA atherosclerosis.
Methods:
Consecutive patients with asymptomatic and symptomatic MCA atherosclerosis (≥50% stenosis) were enrolled. MCA plaque characteristics (location and plaque enhancement) and wall shear stress (WSS) were measured using high-resolution vessel wall and four-dimensional flow magnetic resonance imaging, respectively, at five points (initial, upstream, minimal lumen, downstream, and terminal). These parameters were compared between patients with asymptomatic and symptomatic MCA atherosclerosis with infarctions of different mechanisms (artery-to-artery embolism vs. local branch occlusion).
Results:
In total, 110 patients (46 asymptomatic, 32 artery-to-artery embolisms, and 32 local branch occlusions) were investigated. Plaques were evenly distributed in the MCA of patients with asymptomatic MCA atherosclerosis, more commonly observed in the distal MCA of patients with artery-to-artery embolism, and in the middle MCA of patients with local branch occlusion. Maximum WSS and plaque enhancement were more prominent in the minimum lumen area of patients with asymptomatic MCA atherosclerosis or those with local branch occlusion, and were more prominent in the upstream area in those with artery-to-artery embolism. The elevated variability in the maximum WSS was related to stroke caused by artery-to-artery embolism.
Conclusion:
Stroke caused by artery-to-artery embolism was related to plaque enhancement and the highest maximum WSS at the upstream point of the plaque, and was associated with elevated variability of maximum WSS.
... Recent work has also shown the usefulness of 4D flow MRI in detecting collateral blood supply, another indication of a hemodynamic disturbance in the stroke patient [59,62]. Such collateral blood flow patterns were described in carotid stenosis patients prior to [63] and after surgery [64]. ...
Alterations in cerebral blood flow are common in several neurological diseases among the elderly including stroke, cerebral small vessel disease, vascular dementia, and Alzheimer's disease. 4D flow magnetic resonance imaging (MRI) is a relatively new technique to investigate cerebrovascular disease, and makes it possible to obtain time-resolved blood flow measurements of the entire cerebral arterial venous vasculature and can be used to derive a repertoire of hemodynamic biomarkers indicative of cerebrovascular health.
The information that can be obtained from one single 4D flow MRI scan allows both the investigation of aberrant flow patterns at a focal location in the vasculature as well as estimations of brain-wide disturbances in blood flow. Such focal and global hemodynamic biomarkers show the potential of being sensitive to impending cerebrovascular disease and disease progression and can also become useful during planning and follow-up of interventions aiming to restore a normal cerebral circulation.
Here, we describe 4D flow MRI approaches for analyzing the cerebral vasculature. We then survey key hemodynamic biomarkers that can be reliably assessed using the technique. Finally, we highlight cerebrovascular diseases where one or multiple hemodynamic biomarkers are of central interest.
Abstract
Review of 4D flow MRI hemodynamic biomarkers for cerebrovascular diseases.
... 168,170 In patients with severe carotid artery stenosis, retrograde or absent ophthalmic artery flow on 4D flow MRI can predict intracranial hemodynamic impairment, as suggested by lower relative CBF and cerebrovascular reserve. 171 4D flow MRI revealed the patency of EC-IC bypass and flow direction in the MCA. 172,173 The increased flow of the contralateral ICA and BA supply collateral blood flow. ...
Considering the crosstalk between the flow and vessel wall, hemodynamic assessment of the neurovascular system may offer a well‐integrated solution for both diagnosis and management by adding prognostic significance to the standard CT/MR angiography. 4D flow MRI or time‐resolved 3D velocity‐encoded phase‐contrast MRI has long been promising for the hemodynamic evaluation of the great vessels, but challenged in clinical studies for assessing intracranial vessels with small diameter due to long scan times and low spatiotemporal resolution. Current accelerated MRI techniques, including parallel imaging with compressed sensing and radial k‐space undersampling acquisitions, have decreased scan times dramatically while preserving spatial resolution. 4D flow MRI visualized and measured 3D complex flow of neurovascular diseases such as aneurysm, arteriovenous shunts, and atherosclerotic stenosis using parameters including flow volume, velocity vector, pressure gradients, and wall shear stress. In addition to the noninvasiveness of the phase contrast technique and retrospective flow measurement through the wanted windows of the analysis plane, 4D flow MRI has shown several advantages over Doppler ultrasound or computational fluid dynamics. The evaluation of the flow status and vessel wall can be performed simultaneously in the same imaging modality. This article is an overview of the recent advances in neurovascular 4D flow MRI techniques and their potential clinical applications in neurovascular disease.
Level of Evidence
5
Technical Efficacy Stage
3
... It is clinically desirable to establish MRI-based risk stratification to identify patients who must undergo further PET/ SPECT examination. Recently, time-resolved 3D phasecontrast (4D flow) MRI has been developed, and its scan has been reduced to meet the clinical scanning time (~6 min) by combining acceleration techniques such as radial sampling, k-t acceleration techniques, and compressed sensing [15][16][17][18][19][20][21][22][23]. It provides more objective and reliable information than TOF-MRA by retrospective flow velocity quantification from 3D imaging volumes. ...
... To investigate collateral blood flow circulation, we evaluated flow directions of A1 and the posterior communicating artery (Pcom) of the affected side. The flow patterns were assigned to one of two groups: native flow pattern (antegrade or unclear) or non-native flow pattern (retrograde) (Figs. 2 and 3) [17]. ...
PurposeMRI-based risk stratification should be established to identify patients with internal carotid artery stenosis (ICS) who require further PET or SPECT evaluation. This study assessed whether multiparametric flow analysis using time-resolved 3D phase-contrast (4D flow) MRI can detect cerebral hemodynamic impairment in patients with ICS.Methods
This retrospective study analyzed 26 consecutive patients with unilateral ICS (21 men; mean age, 71 years) who underwent 4D flow MRI and acetazolamide-stress brain perfusion SPECT. Collateral flow via the Willis ring was visually evaluated. Temporal mean flow volume rate (Net), pulsatile flow volume (ΔV), and pulsatility index (PI) at the middle cerebral artery were measured. Cerebral vascular reserve (CVR) was calculated from the SPECT dataset. Patients were assigned to the misery perfusion group if the CVR was < 10% and to the nonmisery perfusion group if the CVR was ≥ 10%. Parameters showing a significant difference in both groups were statistically evaluated.ResultsAffected side ΔV, ratio of affected to contralateral side Net (rNet), and ratio of affected to contralateral side ΔV were significantly correlated to CVR (p = 0.030, p = 0.010, p = 0.015, respectively). Absence of retrograde flow at the posterior communicating artery was observed in the misery perfusion group (p = 0.020). Combined cut-off values of the affected side ΔV (0.18 ml) and rNet (0.64) showed a sensitivity and specificity of 100% and 77.8%, respectively.Conclusion
Multiparametric flow analysis using 4D flow MRI can detect misery perfusion by comprehensively assessing blood flow data, including blood flow volume, pulsation, and collateral flow.
... 30 The recently innovated cardiac phase-resolved three-dimensional (3D) phase-contrast MRI (4D-flow MRI) is a 3D phase-contrast imaging that can provide comprehensive 3D velocity information of the blood flow within the entire vasculatures throughout the cardiac cycle. [31][32][33][34] Unlike CFD simulation, the 4D-flow MRI allows for direct measurements of the WSS and OSI by transforming actual local 3D velocity data measured adjacent to the endothelium. [35][36][37] With an aid of 4D-flow MRI, the purpose of this study was to characterize non-laminar flow dynamics represented by vortex or helical flow, as well as their derivatives such as WSS and OSI in the dilated abdominal aorta as compared with the upstream undilated aorta. ...
Purpose: To characterize the non-laminar flow dynamics and resultant decreased wall shear stress (WSS) and high oscillatory shear index (OSI) of the infrarenal abdominal aortic dilatation, cardiac phase-resolved 3D phase-contrast MRI (4D-flow MRI) was performed.
Methods: The prospective single-arm study was approved by the Institutional Review Board and included 18 subjects (median 67.5 years) with the dilated infrarenal aorta (median diameter 35 mm). 4D-flow MRI was conducted on a 1.5T MRI system. On 3D streamline images, laminar and non-laminar (i.e., vortex or helical) flow patterns were visually assessed both for the dilated aorta and for the undilated upstream aorta. Cardiac phase-resolved flow velocities, WSS and OSI, were also measured for the dilated aorta and the upstream undilated aorta.
Results: Non-laminar flow represented by vortex or helical flow was more frequent and overt in the dilated aorta than in the undilated upstream aorta (P < 0.0156) with a very good interobserver agreement (weighted kappa: 0.82–1.0). The WSS was lower, and the OSI was higher on the dilated aortic wall compared with the proximal undilated segments. In mid-systole, mean spatially-averaged WSS was 0.20 ± 0.016 Pa for the dilated aorta vs. 0.68 ± 0.071 Pa for undilated upstream aorta (P < 0.0001), and OSI on the dilated aortic wall was 0.093 ± 0.010 vs. 0.041 ± 0.0089 (P = 0.013). The maximum values and the amplitudes of the WSS at the dilated aorta were inversely proportional to the ratio of dilated/undilated aortic diameter (r = −0.694, P = 0.0014).
Conclusion: 4D-flow can characterize abnormal non-laminar flow dynamics within the dilated aorta in vivo. The wall of the infrarenal aortic dilatation is continuously and increasingly affected by atherogenic stimuli due to the flow disturbances represented by vortex or helical flow, which is reflected by lower WSS and higher OSI.
Purpose
The impact of carotid endarterectomy (CEA) on choriocapillaris (CC) perfusion was investigated using swept-source optical coherence tomography angiography (SS-OCTA) imaging before and after surgery in patients with clinically significant carotid artery stenosis (CAS).
Methods
In this prospective observational study, patients with clinically significant CAS undergoing unilateral CEA had SS-OCTA imaging performed in both eyes before and within 1 week after surgery. The percent CC flow deficits (CC FD%) and CC thickness were assessed using previously validated algorithms. Multivariable regression analysis was conducted to evaluate the impact of variables on the change in CC measurements.
Results
A total of 112 eyes from 56 patients with an average age of 72.6 ± 6.9 years were enrolled. At baseline, significantly higher CC FD% and thinner CC thickness were observed on the surgical side (eyes ipsilateral to the side of CEA) versus the nonsurgical side (eyes contralateral to the side of CEA) (P = 0.001 and P = 0.03, respectively). Following CEA, a significant reduction in CC FD% and a significant increase in CC thickness were detected on the surgical as compared with the nonsurgical side (P = 0.008 and P = 0.01, respectively). Smoking status positively affected CC FD% change (coefficient of variation [CV] = 0.84, P = 0.01) on the surgical side and negatively affected CC thickness change on both the surgical side (CV = −0.382, P = 0.009) and the nonsurgical side (CV = −0.321, P = 0.04). The degree of stenosis demonstrated a positive influence on CC FD% change (CV = 0.040, P = 0.02) on the surgical side.
Conclusions
Unilateral CEA on the side of clinically significant CAS increases carotid blood flow, which further results in improved CC perfusion.
Objective
This study aimed to evaluate whether CT angiography (CTA) manifestations in anterior cerebral artery a1 segment (A1) were related to the hemodynamics in patients with internal carotid artery stenosis (ICAS).
Methods
A total of 97 cases were selected. The degree of ICAS and symmetry of A1 were evaluated by CTA examination. Hemodynamic indexes were detected by transcranial Doppler (TCD). The differences in CTA presentations of A1 and hemodynamics between the vessels on the stenotic and contralateral sides were analyzed according to the different degrees of stenosis. The degree of ICAS according to the different manifestations of A1 and the hemodynamics of A1’s adjacent vessels were also analyzed.
Results
In the case of unilateral ICAS, the difference in Vm of A1 between the stenotic and the contralateral side was the most significant relative to the stenosis degree. When unilateral ICAS was ≥70%, the presentation of A1 on the stenotic side was more slender or non-visualized compared to that on the contralateral side, while in cases with unilateral stenosis <70% or bilateral stenosis with a similar degree of stenosis, A1 were mainly symmetrical. When A1 on the side of ICAS was slender or non-visualized, the Vm of A1 was significantly slower than that on the contralateral side (P < 0.001).
Conclusion
The CTA manifestations of A1 on the side of ICAS embodied the overall changes of the intracranial hemodynamics after ICAS. A combination of TCD and CTA examination of A1 can assist in judging the location and degree of ICAS.
Both computational fluid dynamics (CFD) and time-resolved, three-dimensional, phase-contrast, magnetic resonance imaging (4D-flow MRI) enable visualization of time-varying blood flow structures and quantification of blood flow in vascular diseases. However, they are totally different. CFD is a method to calculate blood flow by solving the governing equations of fluid mechanics, so the obtained flow field is somewhat virtual. On the other hand, 4D-flow MRI measures blood flow in vivo, thus the flow is real. Recently, with the development and enhancement of computers, medical imaging techniques, and related software, blood flow analysis has become more accessible to clinicians and its usefulness in vascular diseases has been demonstrated. In this review, we have outlined the methods and characteristics of CFD and 4D-flow MRI, respectively. We have discussed the differences in the characteristics between both methods; reviewed the milestones achieved by blood flow analysis in various vascular diseases; and discussed the usefulness, challenges, and limitations of blood flow analysis. We have discussed the difficulties and limitations of current blood flow analysis. We have also discussed our views on future directions.
