In vivo evaluation of quantitative MR angiography in a canine carotid artery stenosis model

Lack of correlation between cerebral arteriovenous malformation angioarchitectural and hemodynamic characteristics and systemic inflammation

PURPOSE

Plasma-based inflammatory biomarkers have gained attention in cerebrovascular pathologies, with studies suggesting links to high-risk features. This study investigates the association between systemic inflammatory markers and cerebral arteriovenous malformation (AVM) angioarchitectural and hemodynamic characteristics.

METHODS

A single-center database of AVM patients (2007-2023) was queried. Patients with unruptured, supratentorial AVMs, baseline quantitative magnetic resonance angiography, and complete blood counts at admission were included. Biomarkers analyzed included white blood cell (WBC) count, absolute neutrophil count (ANC), absolute monocyte count (AMC), absolute lymphocyte count (ALC), and platelet count. Neutrophil-lymphocyte ratio (NLR), lymphocyte-monocyte ratio (LMR), platelet-lymphocyte ratio (PLR), and systemic inflammation index (SII) were calculated. AVM characteristics and hemodynamic properties were assessed.

RESULTS

86 patients met inclusion criteria. No significant correlations were found between systemic inflammatory markers and AVM size, morphology, venous stenosis, or Spetzler-Martin grade. While WBC count and ANC weakly correlated with flow index (p < 0.05), AVM flow showed no consistent associations with inflammatory markers.

CONCLUSION

Systemic inflammatory markers do not consistently correlate with unruptured AVM angioarchitecture or hemodynamics. These findings suggest systemic inflammation may have limited relevance to sporadic AVM pathology. Future studies should explore localized inflammatory biomarkers to better understand AVM behavior.

Evaluation of Sex-Related Differences in Cerebrovascular Bypass Patency: Review of 357 Direct Cerebral Bypasses

BACKGROUND

Demographics and comorbid conditions play a role in vascular health, yet their specific impact on cerebrovascular bypass patency remains unclear.

METHODS

An institutional database of 357 patients with intracranial bypass procedures between August 2001 and May 2022 was retrospectively reviewed. Patients with bypass for all causes (eg, aneurysm, atherosclerotic disease, moyamoya disease) were included. Medical history, surgical technique, and flow-related measurements (intraoperatively and on quantitative magnetic resonance angiography at follow-up) were compared across biological sex and in relation to bypass patency. Bonferroni correction was applied to the initial analysis (P≤0.00167). The remaining analyses were considered exploratory. Propensity score-matched analysis matched cardiovascular risk factors and compared women and men in bypass patency.

RESULTS

Of 357 patients, 141 were men (39.5%) and 216 were women (60.5%) with average age of 49.0±16.7 years and an average follow-up of 1.97 years. Bypass patency at last follow-up was 84.4% (n=114) for men versus 69.2% (n=148) for women (P=0.001). Differences were seen in underlying diagnoses, with more aneurysm and moyamoya cases represented in female sex (P<0.001); irrespective of diagnosis, lower patency rates were seen in women when considering bypass for aneurysm (P=0.032), moyamoya disease (P=0.035), and for atherosclerotic disease (P=0.159). Medical comorbidities were seen at higher rates in men, with comorbidity score of 2.7 versus 2.1 (P<0.001). Cut flow was higher in men 59.2 versus 51.1 (P=0.028), with no differences in intraoperative bypass flow, cut flow index, or follow-up quantitative magnetic resonance angiography. After removing cases using interposition grafts, similar differences were redemonstrated. Propensity score-matched analysis found women have a 2.71 higher chance of bypass occlusion after adjusting for cut flow index (P=0.017 [95% CI, 1.19-6.18]).

CONCLUSIONS

Biological sex appears to play a role in bypass patency, across diagnoses. Women were less likely to have patent bypasses at the last follow-up, despite having fewer medical comorbidities than men and despite having similar intraoperative and perioperative flows.

The Value of Non-Invasive Optimal Vessel Analysis Quantitative Magnetic Resonance Angiography for Studying Flow and Collateral Patterns in Patients with Bilateral Carotid Steno-Occlusive Disease

Background/Objectives: Bilateral steno-occlusive disease of the internal carotid artery (ICA) carries an increased stroke risk with associated high morbidity and mortality. Management of these patients is often complex. In this study, we evaluate the value of non-invasive optimal vessel analysis quantitative magnetic resonance angiography (NOVA-qMRA) for studying flow and collateral patterns in patients with bilateral carotid steno-occlusive disease. Methods: Patients with bilateral ICA-stenosis ≥ 50% who received NOVA-qMRA were included in this study. The volume flow rates (VFRs) of the A2-segment of the anterior cerebral artery (A2-ACA), M1-segment of the middle cerebral artery (M1-MCA), and P2-segment of the posterior cerebral artery (P2-PCA) were analyzed. Demographic, clinical, and treatment data were collected. Results: Twenty-two patients (mean age ± SD: 68 ± 10 years) were included. Nineteen patients (86%) were symptomatic. Thirteen patients (59%) were revascularized; among them, M1-VFR was significantly lower (p-value = 0.01) on the side selected for revascularization (88 mL/min ± 53) compared to the contralateral one (130 mL/min ± 56). P2-VFR was significantly higher (p-value = 0.04) in the treated subgroup (108 mL/min ± 41) than in the non-treated one (83 mL/min ± 34). Conclusions: The present study supports the use of NOVA-qMRA to study flow and collateral patterns in patients with bilateral steno-occlusive carotid disease, especially M1- and P2-VFR. This information may be helpful for decision-making and to tailor revascularization treatment.

The Correlation of Vessel Wall Macrophage Infiltration With Hemosiderin in Arteriovenous Malformations

BACKGROUND

Endothelial dysfunction, induced by high shear stress from increased nidal blood flow, may promote a cycle of inflammation, possibly leading to instability and cerebral arteriovenous malformations (AVMs) rupture. Macrophages, identified with Cluster of Differentiation 68, are key inflammatory components in AVM pathology. We aim to evaluate the relationship of inflammation with AVM flow and hemosiderin.

METHODS

This is a retrospective study of archived tissue. Adult patients (2002-2022) with baseline quantitative magnetic resonance angiography imaging, no embolization, and history of microsurgical resection (n = 17), with both ruptured (n = 9) and unruptured cases (n = 8). Brain AVM sections were stained with Cluster of Differentiation 68 to quantify vessel wall macrophage infiltration and hematoxylin and eosin stain as a control and to quantify hemosiderin. Quantitative magnetic resonance angiography with noninvasive optimal vessel analysis was reviewed, and AVM flow was calculated. Statistical analyses were performed.

RESULTS

There were no significant differences among macrophage infiltration and patient demographics, Spetzler-Martin grade, eloquence, venous stenosis, nidus compactness, volume, and AVM flow. Vessel wall macrophage infiltration positively correlated with patients who presented with confirmed AVM rupture (163.8 ± 46.7 vs. 101.3 ± 49.4, P = 0.017). Increases in vessel wall macrophage infiltration were found to positively correlate with higher grades of hemosiderin (P = 0.023), except for grade 4 hemosiderin. Venous anomaly showed a negative association with macrophage infiltration (P = 0.035).

CONCLUSIONS

These findings suggest a relationship among AVM vessel wall inflammation, hemosiderin, and hemorrhage presentation. Further investigations with larger sample sizes are warranted to understand the role of altered hemodynamics, hemosiderin deposition, and inflammation in AVM vessel walls.

Correlation between nova volume flow rate and TOF signal intensity ratio: value in unilateral internal carotid artery occlusion

BACKGROUND AND PURPOSES

Non-invasive optimal vessel analysis quantitative magnetic resonance angiography (NOVA-QMRA) has emerged as a valuable tool to characterize cerebral hemodynamics in intracranial atherosclerotic disease (ICAD). Our aim was to explore the eventual correlation between volume flow rate (VFR) measured via NOVA-QMRA and signal intensity ratio (SIR) of time-of-flight (TOF) MRA in M1- and P2-segments bilaterally in patients with unilateral internal carotid artery (ICA) occlusion.

MATERIALS AND METHODS

Patients with acute, subacute or chronic unilaterall ICA occlusion receiving NOVA-QMRA between June 2019 and June 2021 were retrospectively included. In bilateral M1- and P2-segments VFR was assessed by means of NOVA-QMRA and a region of interest (ROI) was selected to measure TOF SIR. A correlation between TOF SIR and VFR was tested by means of Pearson correlation coefficient. Mean difference of TOF SIR and VFR between ipsilateral (to occluded ICA) and contralateral M1- and P2-segments was analyzed using a two-sided Welch's t test.

RESULTS

Fifty-five patients with unilateral ICA occlusion were included (acute: 28; subacute: 8; chronic: 19). Both ipsilateral (r = 0.536, p < 0.001) and contralateral (r = 0.757, p < 0.001) TOF SIR correlated significantly with NOVA VFR. This observation proved especially true for patients with chronic ICA occlusion. Both VFR (165.18 vs 110.60, p < 0.001) and TOF SIR (4.96 vs 2.70, p < 0.001) were higher in contralateral than ipsilateral M1-segments; whereas, the contrary was observed for P2-segments (VFR 72.35 vs 102.12, p < 0.001, TOF SIR 2.87 vs 3.39, p = 0.016).

CONCLUSION

The study results showed that TOF SIR significantly correlated with phase-contrast derived flow volume in patients with symptomatic ICA occlusion. This correlation remains the same regardless of the stage of the ischemic stroke (acute vs subacute vs chronic). Furthermore, significantly high VFR and TOF SIR in ipsilateral P2-segments may provide evidence of leptomeningeal collateralization in acute patients. Standardly performed TOF SIR Sequences might be of help for a qualitative evaluation of the flow in M1- and P2-segments in patients with unilateral ICA occlusions. NOVA QMRA allows precise quantitative measurements of the flow in cerebral vessels.

A patient-specific circle of Willis blood flow model in predicting outcomes of balloon test occlusion

BACKGROUND AND PURPOSE

Balloon test occlusion (BTO) evaluates cerebral ischemic tolerance before internal carotid artery (ICA) sacrifice but carries risks like dissection and thrombosis. This study introduces a new approach using a patient-specific circle of Willis (COW) blood flow model, based on non-invasive quantitative MR angiography (qMRA) measurements, to predict the outcomes of BTO.

METHODS

We developed individualized COW blood flow models for 43 patients undergoing BTO. These models simulated blood flow and pressure under normal conditions and with the ICA occlusion. We then compared the model's predictions of blood flow changes due to the simulated ICA occlusion to actual qMRA measurements before the BTO.

RESULTS

For all 31 BTO failures, the ipsilateral hemisphere showed an average flow decrease of 15 ± 10% (mean ± standard deviation), compared to 3 ± 2% in the contralateral hemisphere. In all 12 BTO passes, these figures were 6 ± 3% and 1 ± 0.8%, respectively. Notably, all BTO passes had less than a 10% reduction in the ipsilateral hemisphere. In contrast, 65% of BTO failures and 67% single-photon emission computed tomography (SPECT) failures exhibited a decrease of 10% or more in the same region.

CONCLUSION

Blood flow reduction exceeding 10% in the ipsilateral hemisphere during BTO is a strong predictor of failure in both BTO and SPECT. Our patient-specific COW blood flow models, incorporating detailed flow and arterial geometry data, offered valuable insights for predicting BTO outcomes. These models are especially beneficial for situations where conducting BTO or SPECT is clinically impractical.

Flow-augmentation STA-MCA bypass for acute and subacute ischemic stroke due to internal carotid artery occlusion and the role of advanced neuroimaging with hemodynamic and flow-measurement in the decision-making: preliminary data

Background

A major clinical challenge is the adequate identification of patients with acute (<1 week) and subacute (1-6 weeks) ischemic stroke due to internal carotid artery (ICA) occlusion who could benefit from a surgical revascularization after a failure of endovascular and/or medical treatment. Recently, two novel quantitative imaging modalities have been introduced: (I) quantitative magnetic resonance angiography (qMRA) with non-invasive optimal vessel analysis (NOVA) for quantification of blood flow in major cerebral arteries (in mL/min), and (II) blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging to assess cerebrovascular reactivity (CVR). The aim of this study is to present our cohort of patients who underwent surgical revascularization in the acute and subacute phase of ischemic stroke as well as to demonstrate the importance of hemodynamic and flow assessment for the decision-making regarding surgical revascularization in patients with acute and subacute stroke and ICA-occlusion.

Methods

Symptomatic patients with acute and subacute ischemic stroke because of persistent ICA-occlusion despite optimal medical/endovascular recanalization therapy who were treated at the Neuroscience Clinical Center of the University Hospital Zurich underwent both BOLD-CVR and qMRA-NOVA to study the hemodynamic and collateral vessel status. Patients selected for surgical revascularization according to our previously published flowchart were included in this prospective cohort study. Repeated NOVA and BOLD-CVR investigations were done after bypass surgery as follow up as well as clinical follow up. Continuous BOLD-CVR and qMRA-NOVA variables were compared using paired Student t-test.

Results

Between May 2019 and September 2022, superficial temporal artery-middle cerebral artery (STA-MCA) bypass surgery was performed in 12 patients with acute and subacute stroke because of ICA-occlusion despite of optimal endovascular and/or medical treatment prior to the surgery. Impaired BOLD-CVR in the occluded vascular territory [MCA territory: ipsilateral vs. contralateral: -0.03±0.07 vs. 0.11±0.07 %BOLD/mmHgCO2, P<0.001] as well as reduced hemispheric flow with qMRA-NOVA (ipsilateral vs. contralateral: 228.00±54.62 vs. 384.50±70.99 mL/min, P=0.01) were measured indicating insufficient collateralization. Post-operative qMRA-NOVA showed improved hemispheric flow (via bypass) (pre-bypass vs. post-bypass: 236.60±76.45 vs. 334.20±131.33 mL/min, P=0.02) and the 3-month-follow-up with BOLD-CVR showed improved cerebral hemodynamics (MCA territory: pre-bypass vs. post-bypass: -0.01±0.05 vs. 0.06±0.03 %BOLD/mmHgCO2, P=0.02) in all patients studied.

Conclusions

Quantitative assessment with BOLD-CVR and qMRA-NOVA allows us to evaluate the pre- and post-operative cerebral hemodynamics and collateral vessel status in patients with acute/subacute stroke due to ICA occlusion who may benefit from surgical revascularization after failure of endovascular/medical treatment.

Quantitative Blood Flow Reduction in Selective Embolization of Intranidal Fistula of Cerebral Arteriovenous Malformations: Case Series

BACKGROUND AND OBJECTIVES

Arteriovenous malformations (AVMs) are often associated with high-flow intranidal fistulas (INFs). Although INF embolization has been suggested to provide higher reduction of total AVM flow compared with regular pedicle embolization, this effect has not previously been quantified. The aim of this study was to characterize the effect of AVM INF embolization on total AVM flow.

METHODS

This study is an Institutional Review Board-approved, retrospective case series of patients from 2010 to 2022 with AVMs, both with and without INFs, who underwent quantitative magnetic resonance angiography and endovascular embolization.

RESULTS

Twenty patients accounted for 35 separate embolization sessions: 13 patients with INFs underwent a total 21 embolizations and 12 patients without INFs had 14 embolizations. No significant differences were found between groups on age, sex, laterality, drainage pattern, and Spetzler-Martin grade. However, AVMs with INFs were larger than the control group (12.7 vs 8.37 cm 3 , P = .049). Baseline pre-embolization AVM flow significantly differed between AVM with INF vs control groups (522 vs 320 cc/min, P = .005). Similarly, postembolization AVM flow also differed between AVM with INF and control groups (392 vs 224 cc/min, P = .008), with a larger decrease in flow per vessel per embolization session within the AVM INF group compared with controls (101.5 vs 33.2 cc/min, P < .001). Repeated measure analysis of variance showed significant differences pre-embolization and postembolization AVM flow between those with INFs vs controls ( P < .001).

CONCLUSION

This study represents the first to examine the effect of INF embolization on total AVM flow. AVMs with INFs showed higher baseline flow, and targeted embolization toward INFs significantly lowered AVM flow in comparison with controls without INFs. The results of this study emphasize the importance of recognizing the presence of INFs within AVMs and their embolization to reduce AVM flow as part of a multistep management paradigm.

Rupture-Risk Stratifying Patients with Cerebral Arteriovenous Malformations Using Quantitative Hemodynamic Flow Measurements

Arteriovenous malformations (AVMs) are high-pressure, low-resistance arterial-venous shunts without intervening capillaries. Up to 60% of AVMs present with an intracranial hemorrhage; however, noninvasive neuroimaging has increasingly diagnosed incidental AVMs. AVM management depends on weighing the lifetime rupture risk against the risks of intervention. Although AVM rupture risk relies primarily on angioarchitectural features, measuring hemodynamic flow is gaining traction. Accurate understanding of AVM hemodynamic flow parameters will help endovascular neurosurgeons and interventional neuroradiologists stratify patients by rupture risk and select treatment plans. This review examines various neuroimaging modalities and their capabilities to quantify AVM flow, as well as the relationship between AVM flow and rupture risk. Quantitative hemodynamic studies on the relationship between AVM flow and rupture risk have not reached a clear consensus; however, the preponderance of data suggests that higher arterial inflow and lower venous outflow in the AVM nidus contribute to increased hemorrhagic risk. Future studies should consider using larger sample sizes and standardized definitions of hemodynamic parameters to reach a consensus. In the meantime, classic angioarchitectural features may be more strongly correlated with AVM rupture than the amount of blood flow.

Quantified flow and angioarchitecture show similar associations with hemorrhagic presentation of brain arteriovenous malformations

INTRODUCTION

The purpose of our study was to elucidate the impact of brain arteriovenous malformation (BAVM) flow and wall shear stress (WSS) on angioarchitecture and to evaluate their association with hemorrhagic presentations.

MATERIALS AND METHODS

Forty-one patients with BAVMs were evaluated by phase-contrast MR angiography. Volume flow rate and WSS were quantified. Angioarchitectural features such as location, angiogenesis, venous stenosis, venous ectasia, venous phlebitis, venous rerouting, exclusive deep vein and venous sac were evaluated by two neuroradiologists. The correlation between BAVM flow and size was evaluated with Spearman correlation coefficients. Differences of size, flow, and WSS between the hemorrhagic and non-hemorrhagic groups, the seizure and non-seizure groups, and between the different groups based on angioarchitecture were evaluated with Mann-Whitney U tests. Accuracy in predicting hemorrhage was evaluated with receiver operating characteristic curves.

RESULT

BAVM flow was highly correlated with volume (ρ = 0.77). Higher flow was more commonly associated with angiogenesis, venous ectasia, venous rerouting, and venous phlebitis. Flow and angioarchitecture showed similar efficacy in differentiating hemorrhagic from non-hemorrhagic BAVMs. WSS did not demonstrate differences across any clinical groups.

CONCLUSION

Flow quantification and angioarchitecture analysis of BAVMs showed similar efficacy as evaluated by associations with hemorrhagic presentation. High flow affects both arterial and venous angioarchitecture, reflecting the nature of low vascular resistance in BAVMs.

Flow augmentation STA-MCA bypass evaluation for patients with acute stroke and unilateral large vessel occlusion: a proposal for an urgent bypass flowchart

OBJECTIVE

Endovascular recanalization trials have shown a positive impact on the preservation of ischemic penumbra in patients with acute large vessel occlusion (LVO). The concept of penumbra salvation can be extended to surgical revascularization with bypass in highly selected patients. For selecting these patients, the authors propose a flowchart based on multimodal MRI.

METHODS

All patients with acute stroke and persisting internal carotid artery (ICA) or M1 occlusion after intravenous lysis or mechanical thrombectomy undergo advanced neuroimaging in a time window of 72 hours after stroke onset including perfusion MRI, blood oxygenation level-dependent functional MRI to evaluate cerebrovascular reactivity (BOLD-CVR), and noninvasive optimal vessel analysis (NOVA) quantitative MRA to assess collateral circulation.

RESULTS

Symptomatic patients exhibiting persistent hemodynamic impairment and insufficient collateral circulation could benefit from bypass surgery. According to the flowchart, a bypass is considered for patients 1) with low or moderate neurological impairment (National Institutes of Health Stroke Scale score 1-15, modified Rankin Scale score ≤ 3), 2) without large or malignant stroke, 3) without intracranial hemorrhage, 4) with MR perfusion/diffusion mismatch > 120%, 5) with paradoxical BOLD-CVR in the occluded vascular territory, and 6) with insufficient collateral circulation.

CONCLUSIONS

The proposed flowchart is based on the patient's clinical condition and multimodal MR neuroimaging and aims to select patients with acute stroke due to LVO and persistent inadequate collateral flow, who could benefit from urgent bypass.

Prediction of Long-Term Restenosis After Carotid Endarterectomy Using Quantitative Magnetic Resonance Angiography

Background

To detect restenosis after carotid endarterectomy (CEA), long-term monitoring is required. However, non-selective follow-up is controversial and can be limited by costs and logistical considerations.

Objective

To examine the value of immediate perioperative vessel flow measurements after CEA using quantitative magnetic resonance angiography (QMRA) to detect patients at risk of long-term restenosis.

Methods

A prospective cohort study with long-term sonographic follow-up after CEA for symptomatic internal carotid artery stenosis (ICAs) > 50%. In all patients, vessel flow has been assessed both pre- and postoperatively using QMRA within ±3 days of surgery. Data on QMRA assessment were analyzed to identify patients at risk of restenosis for up to 10 years.

Results

Restenosis was recorded in 4 of 24 patients (17%) at a median follow-up of 6.8 ± 2.6 years. None of them experienced an ischemic event. Perioperative flow differences were significantly greater in patients without long-term restenosis, both for the ipsilateral ICA (p < 0.001) and MCA (p = 0.03), compared to those with restenosis (p = 0.22 and p = 0.3, respectively). The ICA mean flow ratio (p = 0.05) tended to be more effective than the MCA ratio in predicting restenosis over the long term (p = 0.35).

Conclusion

Our preliminary findings suggest that QMRA-based mean flow increases after CEA may be predictive of restenosis over the long term. Perioperative QMRA assessment could become an operator-independent screening tool to identify a subgroup of patients at risk for restenosis, in whom long-term monitoring is advised.

Use of quantitative magnetic resonance angiography in patients with symptomatic intracranial arterial stenosis who undergo stenting: Presentation of three cases

Intracranial atherosclerotic disease (ICAD) is an important cause of ischemic stroke. The etiology of stroke in patients with ICAD could be due to several mechanisms including hypoperfusion, artery-to-artery embolism, and plaque extension over small penetrating artery ostia. Management of symptomatic ICAD includes medical and endovascular management. Quantitative magnetic resonance angiography (MRA) is a technique that allows for non-invasive measurement of large vessel blood flow in the head and neck. Here, we describe procedural and clinical outcomes on three patients who presented with symptomatic ICAD and were treated with angioplasty and stenting. Quantitative MRA was used pre- and post- procedurally to assess the effects of stenting on the intracranial blood flow. Quantitative measures of intracranial blood flow may serve as an additional triage tool in the evaluation of patients with symptomatic ICAD.

Comparative efficacy of autologous versus cadaveric saphenous vein grafts in cerebral revascularization surgery

OBJECTIVE

Cerebral bypasses are performed for the purpose of either flow augmentation for ischemic cerebrovascular disease or flow replacement for vessel sacrifice during complex aneurysm or tumor surgery. Saphenous vein grafts (SVGs) are commonly used interposition grafts. The authors of this study sought to compare the efficacy of autologous versus cadaveric SVGs in a large series of cerebral bypasses using interposition vein grafts with long-term angiographic follow-up.

METHODS

All intracranial bypass procedures performed between 2001 and 2018 were reviewed. Demographic, clinical, angiographic, and operative data were recorded and then analyzed according to SVG type.

RESULTS

A total of 308 consecutive intracranial bypasses were performed during the study period, 53 (17.2%) of which were bypasses with an interposition SVG (38 autologous, 15 cadaveric). At a median follow-up of 2.2 months (IQR 0.2-29.1), 39 (73.6%) bypasses were patent (26 [68.4%] autologous, 13 [86.7%] cadaveric, p = 0.30). Comparing autologous and cadaveric SVG recipients, there were no statistically significant differences in age (p = 0.50), sex (p > 0.99), history of smoking (p = 0.75), hypertension (p > 0.99), diabetes mellitus (p = 0.13), indication for bypass (p = 0.27), or SVG diameter (p = 0.65). While there were higher intraoperative (autologous, 100.0 ml/min, IQR 84.3-147.5; cadaveric, 80.0 ml/min, IQR 47.3-107.8; p = 0.11) and postoperative (autologous, 142.2 ml/min, IQR 76.8-160.8; cadaveric, 92.0 ml/min, IQR 69.2-132.2; p = 0.42) volumetric flow rates in the autologous SVGs compared to those in the cadaveric SVGs, the difference between the two groups did not reach statistical significance. In addition, the blood flow index, or ratio of postoperative to intraoperative blood flow, for each bypass was similar between the groups (autologous, 1.3, IQR 0.9-1.6; cadaveric, 1.5, IQR 1.0-2.3; p = 0.37). Kaplan-Meier estimates showed no difference in bypass patency rates over time between autologous and cadaveric SVGs (p = 0.58).

CONCLUSIONS

Cadaveric SVGs are a reasonable interposition graft option in cerebral revascularization surgery when autologous grafts are not available.

Changes in Cognition and Hemodynamics 1 Year after Carotid Endarterectomy for Asymptomatic Stenosis

OBJECTIVES

 The impact of a change in hemodynamics on cognitive skills in patients with asymptomatic carotid stenosis (ACS) after carotid endarterectomy (CEA) remains unclear. The aim of this study was to evaluate the results of CEA for ACS at 1 year by assessing the changes in anterior, middle, and posterior cerebral artery blood flow in tandem with changes in cognitive efficiency.

METHODS

 Flow volume in cerebral arteries using quantitative magnetic resonance angiography was measured in a group of 14 males and 5 females before and at 1 year after CEA for ACS. Cognitive efficiency was assessed by Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). The values of flow volume were processed using simple ratio (SR) and were used for covariance analyses with changes in cognitive skills after CEA.

RESULTS

 A significant improvement in cognitive efficiency indexes of immediate memory and visuospatial perception at 1 year after CEA for ACS was observed. Simultaneously, a significant deterioration of speech index was noted. During the analysis of association between flow and cognition, the highest correlation could be seen between the middle cerebral artery (MCA) flow and the visuospatial perception. A change in posterior cerebral artery (PCA) flow was associated with an increase in immediate memory index and anterior cerebral artery (ACA) flow change with the speech index.

CONCLUSION

 Convergence of data supporting the association between revascularization and cognitive improvement were added in a small, single-center cohort of ACS patients undergoing CEA. No significant differences in cognition were seen between preoperative findings and at 1 year after CEA. Visuospatial perception improvement was linked to flow change in MCA, immediate memory improvement to flow change in PCA, and speech index change to flow change in ACA. Methodical limitations of this small study preclude formulating larger generalizations. Hemodynamic factors in CEA should be assessed in a larger-scale study.

Inter- and Intra-Rater Reliability of Individual Cerebral Blood Flow Measured by Quantitative Vessel-Flow Phase-Contrast MRI

Vessel flow quantification by two-dimensional (2D) phase-contrast magnetic resonance imaging (PC-MRI) using a three-dimensional (3D) magnetic resonance angiography (MRA) model to measure cerebral blood flow has unclear analytical reliability. The present study aimed to determine the inter- and intra-rater reliability of quantitative vessel-flow PC-MRI and potential factors influencing its consistency. We prospectively recruited 30 Asian participants (aged 20-90 years; 16 women; 22 healthy and 8 stroke patients) for performing 1.5-T MR equipped with a head coil. Each participant was first scanned for time-of-flight magnetic resonance angiography (TOF-MRA) images for localization of intracranial arteries. The 2D PC-MRI for each cerebral artery (total 13 arteries in fixed order) was performed twice by two well-trained operators in optimal position. Using the same 3D MRA as a map and facilitated with the non-invasive optimal vessel analysis (NOVA) system, each scan was taken on a plane perpendicular to the target artery. Two consecutive full 13-artery scans were performed at least 15 min apart after participants were removed from the scanner table and then repositioned. A total of four PC flow images obtained from each target artery were transmitted to a workstation facilitated with the NOVA system. Flow data were calculated semi-automatically by the NOVA system after a few simple steps. Two-way mixed-effect models and standard errors of measurements were used. In 13 cerebral arteries, repeatability, using the intra-rater estimate expressed as the average-measures intraclass correlation coefficient, ranged from 0.641 to 0.954, and reproducibility, using the inter-rater estimate, ranged from 0.672 to 0.977. Except in the middle cerebral artery and the distal segment of the anterior cerebral artery, repeatability and reproducibility were excellent (intraclass correlation coefficient exceeded 0.8). The use of quantitative vessel-flow PC-MRI is a precise means to measure blood flow in most target cerebral arteries. This was evidenced by inter-rater and intra-rater correlations that were good/excellent, indicating good reproducibility and repeatability.

Infarct Patterns in Patients with Atherosclerotic Vertebrobasilar Disease in Relation to Hemodynamics

Introduction

Distal territory blood flow is independently associated with subsequent strokes in symptomatic vertebrobasilar atherosclerotic disease. We aimed to assess infarct patterns in relation to hemodynamic status in the prospective Vertebrobasilar Flow Evaluation and Risk of Transient Ischemic Attack and Stroke (VERiTAS) study.

Methods

Distal territory blood flow was measured using quantitative magnetic resonance angiography (MRA) in 72 patients with symptomatic atherosclerotic vertebrobasilar disease, and then dichotomized into normal (n = 54) and low (n = 18) flow. Patients were followed longitudinally on standard medical management. Two observers blinded to flow status independently reviewed the imaging performed at the time of subsequent strokes, in order to adjudicate the likely mechanism based on infarct patterns. The frequency of stroke mechanisms was qualitatively compared based on flow status.

Results

During a median follow-up period of 23 months, 10/72 patients had a subsequent stroke; 5 of these had low distal flow. Infarct patterns were adjudicated to be consistent with hemodynamic (n = 2), embolic (n = 4), and junctional plaque/perforator (n = 4) infarcts. Hemodynamic infarcts were seen in 40% (2/5) low-flow patients, in comparison to 0% (0/5) normal-flow patients.

Conclusion

In contrast to normal-flow patients, those with low distal flow seem to be uniquely susceptible to hemodynamic infarctions, although other patterns of infarction can also be seen in these hemodynamically impaired patients.

Contrast Time-Density Time on Digital Subtraction Angiography Correlates With Cerebral Arteriovenous Malformation Flow Measured by Quantitative Magnetic Resonance Angiography, Angioarchitecture, and Hemorrhage

BACKGROUND

Digital subtraction angiography (DSA) currently provides angioarchitectural features of cerebral arteriovenous malformations (AVMs) but its role in the hemodynamic evaluation of AVMs is poorly understood.

OBJECTIVE

To assess contrast time-density time (TT) on DSA relative to AVM flow measured using quantitative magnetic resonance angiography (QMRA).

METHODS

Patients seen at our institution between 2007 and 2014 with a supratentorial AVM and DSA and QMRA obtained prior to any treatment were retrospectively reviewed. Regions of interest were selected on the draining veins at the point closest to the nidus. TT on DSA was defined as time needed for contrast to change image intensity from 10% to 100%, 100% to 10%, and 25% to 25%. TT was correlated to AVM total flow, angioarchitectural features, and hemorrhage.

RESULTS

Twenty-eight patients (mean age 35.6 yr) were included. Six patients presented with hemorrhage. Mean AVM volume was 11.42 mL (range 0.3-57.7 mL). Higher total AVM flow significantly correlated with shorter TT100%-10% and TT25%-25% (P = .02, .02, respectively). Presence of venous stenosis correlated significantly with shorter TT100%-10% (P = .04) and TT25%-25% (P = .04). AVMs with a single draining vein exhibited longer TT25%-25% compared to those with multiple draining veins (P = .04). Ruptured AVMs had significantly shorter TT10%-100% compared to unruptured AVMs (P = .05).

CONCLUSION

TT on DSA correlates with cerebral AVM flow measured using QMRA and with AVM angioarchitecture and hemorrhagic presentation. Thus, TT may be used to indirectly estimate AVM flow during angiography in real-time and may also be an indicator of important AVM characteristics associated with outflow resistance and increased rupture risk, such as venous stenosis.

Role of Resistivity Index Analysis in the Prediction of Hemodynamically Significant Venous Sinus Stenosis in Patient With Idiopathic Intracranial Hypertension

BACKGROUND

The resistivity index (RI) in cerebral venous sinus stenosis (VSS) has not been studied in patients with idiopathic intracranial hypertension (IIH).

OBJECTIVE

To evaluate the role of RI measured by quantitative magnetic resonance venogram (QMRV) as a noninvasive tool in the diagnosis of venous hypertension associated with VSS in IIH.

METHODS

Retrospective evaluation of 13 consecutive IIH patients who underwent venous sinus stenting at our institution between 2013 and 2018.

Patients’ demographics, clinical presentation, cerebral mean venous sinus pressure (MVP), and RI both pre- and poststenting were recorded. The baseline RI was also compared to a control group.

RESULTS

Among 13 patients of IIH, 11 had unilateral VSS in dominant sinus, whereas 2 had bilateral VSS. RI was significantly higher in IIH patients compared to the control group in the superior sagittal (SSS) and transverse sinuses (TS) (0.21 vs 0.11, P = .01 and 0.22 vs 0.13, P = .03, respectively). The MVP (in mm Hg) decreased significantly after venous sinus stenting in the SSS (41.9 to 22.5, P &lt; .001) and TS (39.4 to 19.5, P &lt; .001), which was also associated with a significant reduction of the RI (0.22 vs 0.17, P &lt; .01 in SSS and 0.23 vs 0.17, P = .03 in TS) poststenting.

CONCLUSION

RI calculated using QMRV can serve as a noninvasive tool to aid in the diagnosis of hemodynamically significant VSS. The study had a small sample size, and larger multicenter studies would be required to validate the results further.

Quantitative evaluation of blood flow in each cerebral branch associated with zone 1-2 thoracic endovascular aortic repair

OBJECTIVES

Optimal methods to quantitatively evaluate the blood flow in each cerebral artery after zone 1-2 thoracic endovascular aortic repair (TEVAR) remain unknown. Our objective was to evaluate the differences between preoperative and postoperative cerebral artery blood flows after zone 1-2 debranching TEVAR (dTEVAR).

METHODS

Between January 2016 and August 2018, a prospective analysis of the blood flow in both the internal carotid artery and the vertebral artery in 16 patients before and after zone 1-2 dTEVAR was conducted. Zone 1 dTEVAR with right axillary artery-left common carotid artery-left axillary artery (RAxA-LCCA-LAxA) bypass was performed on 7 patients. Zone 2 dTEVAR was performed on 9 patients: 4 underwent RAxA-LAxA bypass and 5 underwent LCCA-LAxA bypass. Quantitative magnetic resonance angiography was performed before and after zone 1-2 dTEVAR.

RESULTS

Total intracranial blood flow was preserved postoperatively [The median (interquartile range) preoperatively vs postoperatively: 621 (549-686) vs 638 (539-703) ml/min, not significant]. The anterior [469 (400-504) vs 475 (404-510) ml/min, not significant] and posterior cerebral blood flows [157 (121-199) vs 163 (123-210) ml/min, not significant] were also maintained postoperatively. In the 3 debranching procedures, the postoperative anterior and posterior cerebral blood flows were maintained at rates similar to preoperative rates, with the proportion of anterior and posterior cerebral circulations reaching almost 75% and 25%, respectively. No significant differences between preoperative and postoperative distributions of internal carotid artery blood flows were observed. Regarding vertebral artery blood flows, the distribution of blood flow through the left vertebral artery was significantly lower postoperatively than preoperatively; however, the postoperative right vertebral artery blood flow distribution significantly increased compared with the preoperative flow.

CONCLUSIONS

In zone 1-2 dTEVAR, total intracranial blood flow was preserved postoperatively, and the postoperative anterior and posterior cerebral circulations were maintained at rates similar to their preoperative rates.

Hemodynamic characteristics associated with cerebral aneurysm formation in patients with carotid occlusion

OBJECTIVE

The pathogenesis of cerebral aneurysms in patients with internal carotid artery (ICA) occlusion is hypothesized to be hemodynamic. For the first time, the authors quantify the hemodynamic characteristics associated with aneurysm formation in patients with ICA occlusion.

METHODS

Records of patients with unilateral ICA stenosis or occlusion ≥ 90% who underwent hemodynamic assessment before treatment using quantitative MR angiography were retrospectively reviewed. The patients were classified into 2 groups based on the presence or absence of aneurysms. The hemodynamic parameters of flow volume rate, flow velocity, and wall shear stress (WSS) were measured in each vessel supplying collateral flow-bilateral A1 segments and bilateral posterior communicating arteries-and then compared between the groups.

RESULTS

A total of 36 patients were included (8 with and 28 without aneurysms). The mean flow (72.3 vs 48.9 ml/min, p = 0.10), flow velocity (21.1 vs 12.7 cm/sec, p = 0.006), and WSS (22.0 vs 12.3 dynes/cm2, p = 0.003) were higher in the A1 segment contralateral to the side of the patent ICA in patients with versus without aneurysms. All de novo or growing aneurysms in our cohort were located on the anterior communicating artery (ACoA) or P1 segment.

CONCLUSIONS

Flow velocity and WSS are significantly higher across the ACoA in patients who harbor an aneurysm, and de novo or growing aneurysms are often located on collateral vessels. Thus, robust primary collaterals after ICA occlusion may be a contributing factor in cerebral aneurysm formation.

Combined native magnetic resonance angiography, flow-quantifying, and perfusion-imaging for impending second-stroke assessment

This special report introduces native flow quantitative imaging for evaluating stroke risk. Moreover, the advantage of combining three imaging techniques [magnetic resonance angiography (MRA), phase-contrast (PC) flow imaging, and arterial spin-labeling imaging] is shown to be beneficial for responding to ischemia and preserving viable neurons. These quantitative imaging techniques provide authoritative information for diagnosing impending stroke and selecting appropriate treatment.

Single Vessel Double Anastomosis for Flow Augmentation – A Novel Technique for Direct Extracranial to Intracranial Bypass Surgery

BACKGROUND

A double anastomosis using a single superficial temporal artery (STA) donor branch for both a proximal side-to-side (S2S) and a distal end-to-side anastomosis is a novel direct bypass technique for use in selected patients necessitating flow augmentation.

OBJECTIVE

To describe the single-vessel double anastomosis (SVDA) technique, including its indications, advantages, and limitations, in addition to reporting our cases series of patients who underwent a SVDA bypass surgery.

METHODS

Patients undergoing a SVDA bypass at a single institution between January 2010 and February 2016 were retrospectively reviewed. Intraoperative flow data was collected, including STA cut-flow, bypass flows, and cut flow index (CFI). Bypass patency was assessed by cerebral angiography and quantitative magnetic resonance angiography with noninvasive optimal vessel analysis. Adverse events occurring during the hospital stay and clinical status at last follow up was recorded.

RESULTS

Seven patients underwent SVDA bypass. Mean follow-up was 14.5 mo. Initial CFI for the S2S bypasses averaged 0.56 ± 0.25 and CFI after the SVDA averaged 1.15 ± 0.24. There was a statistically significant average difference in CFI before and after the SVDA bypass (p < .013). Thirteen bypasses (93%) were patent postoperatively, and remained patent at last follow up. Four patients experienced various postoperative complications. None of the patients had a new stroke since hospital discharge.

CONCLUSION

SVDA is a novel technique that can be advantageous for selected cases of extracranial-to-intracranial bypass. Expertise in bypass procedures is a necessary prerequisite. Graft patency rates and complications appear comparable to other bypass techniques.

Hemodynamic analysis of carotid artery after endarterectomy: a preliminary and quantitative imaging study based on computational fluid dynamics and magnetic resonance angiography

Background

The carotid blood flow following carotid endarterectomy (CEA) is not fully understood. Computational fluid dynamics (CFD) is a promising method to study blood flow. This study is to investigate local hemodynamic characteristics after CEA via the use of unenhanced magnetic resonance angiography (MRA) and CFD.

Methods

Eight carotid arteries with atherosclerosis and sixteen normal carotid arteries were included in this study. Time-of-flight (TOF) and phase contrast (PC) MRA were applied for the measurement of three-dimensional artery geometries and velocity profile under CFD simulation. The hemodynamic parameters of the proximal internal carotid artery (ICA) including velocity, ICA/common carotid artery (CCA) velocity ratio, mean, maximum, minimum and gradient of wall shear stress (WSS_mean, WSS_max, WSS_min and WSSG) were calculated before and after CEA. Morphologic characteristics of the carotid including bifurcation angle, tortuosity and planarity were also analyzed.

Results

Compared with pre-CEA, there was a significant reduction in post-CEA velocity, WSS_max, WSS_mean, and WSSG, by 87.24%±13.38%, 86.86%±14.97%, 57.32%±56.71% and 69.74%±37.03% respectively, whereas WSS_min was almost unchanged. ICA/ CCA velocity ratios increased significantly after CEA. We also found that the post-CEA flow conditions were positively remodelled to approximate the conditions in normal arteries. The correlation between PC-MRA and CFD was excellent for the measurement of maximum velocity at the external carotid artery (r=0.846).

Conclusions

Our preliminary results indicated that major flow dynamics were restored shortly following CEA, and CFD based on MRA measurements could be useful for quantitative evaluation of hemodynamic outcomes after CEA.

Multiple blood flow measurements before and after carotid artery stenting via phase-contrast magnetic resonance imaging: An observational study

After carotid artery stenting, the procurement of information about blood flow redistribution among brain-feeding arteries and its time trend is essential to understanding a patient’s physiological background and to determine their care regimen. Cerebral blood flow has been measured twice following carotid artery stenting in few previous studies, with some discrepancies in the results. The purpose of this study was to measure cerebral blood flow at multiple time points after carotid artery stenting, and to elucidate the time trend of cerebral blood flow and redistribution among arteries. Blood flow rates in 11 subjects were measured preoperatively, at one day, one week, and about three months, respectively after carotid artery stenting by using phase-contrast magnetic resonance imaging. The target vessels were the bilateral internal carotid arteries, the basilar artery, and the bilateral middle cerebral arteries. Lumen was semi-automatically defined using an algorithm utilizing pulsatility. The results showed that blood flow rates in the stented internal carotid artery and the ipsilateral middle cerebral artery increased following carotid artery stenting. Blood flow rates in the contralateral internal carotid artery and the basilar artery gradually declined, and they were lower than the preoperative values at three months after stenting. The sum of blood flow rates of the bilateral internal carotid arteries and the basilar artery increased after carotid artery stenting, and then decreased over the next three months. There was no significant change in the blood flow rate in the contralateral middle cerebral artery. From these results, it was concluded that redistribution among the bilateral internal carotid arteries and the basilar artery occurs after carotid artery stenting, and that it takes months thereafter to reach another equilibrium.

Quantitative magnetic resonance angiography as a potential predictor for cerebral hyperperfusion syndrome: a preliminary study

OBJECTIVE

Cerebral hyperperfusion syndrome (CHS) is a rare but devastating complication of carotid endarterectomy (CEA). This study sought to determine whether quantitative hemodynamic assessment using MR angiography can stratify CHS risk.

METHODS

In this prospective trial, patients with internal carotid artery (ICA) stenosis were randomly selected for pre- and postoperative quantitative phase-contrast MR angiography (QMRA). Assessment was standardized according to a protocol and included Doppler/duplex sonography, MRI, and/or CT angiography and QMRA of the intra- and extracranial supplying arteries of the brain. Clinical and radiological data were analyzed to identify CHS risk factors.

RESULTS

Twenty-five of 153 patients who underwent CEA for ICA stenosis were randomly selected for pre- and postoperative QMRA. QMRA data showed a 2.2-fold postoperative increase in blood flow in the operated ICA (p < 0.001) and a 1.3-fold increase in the ipsilateral middle cerebral artery (MCA) (p = 0.01). Four patients had clinically manifested CHS. The mean flow increases in the patients with CHS were significantly higher than in the patients without CHS, both in the ICA and MCA (p < 0.001). Female sex and a low preoperative diastolic blood pressure were the clearest clinical risk factors for CHS, whereas the flow differences and absolute postoperative flow values in the ipsilateral ICA and MCA were identified as potential radiological predictors for CHS.

CONCLUSIONS

Cerebral blood flow in the ipsilateral ICA and MCA as assessed by QMRA significantly increased after CEA. Higher mean flow differences in ICA and MCA were associated with the development of CHS. QMRA might have the potential to become a noninvasive, operator-independent screening tool for identifying patients at risk for CHS.

Correlation Between Contrast Time-Density Time on Digital Subtraction Angiography and Flow: An in Vitro Study

BACKGROUND AND PURPOSE

Digital subtraction angiography (DSA) provides an excellent anatomic characterization of cerebral vasculature, but hemodynamic assessment is often qualitative and subjective. Various clinical algorithms have been produced to semiquantify flow from the data obtained from DSA, but few have tested them against reliable flow values.

METHODS

An arched flow model was created and injected with contrast material. Seventeen injections were acquired in anterior-posterior and lateral DSA projections, and 4 injections were acquired in oblique projection. Image intensity change over the angiogram cycle of each DSA run was analyzed through a custom MATLAB code. Time-density plots obtained were divided into 3 components (time-density times, TDTs): TDT_10%-100% (time needed for contrast material to change image intensity from 10% to 100%), TDT_100%-10% (time needed for contrast material to change image intensity from 100% to 10%), and TDT_25%-25% (time needed for contrast material to change from 25% image intensity to 25%). Time-density index (TDI) was defined as model cross-sectional area to TDT ratio, and it was measured against different flow rates.

RESULTS

TDI_10%-100%, TDI_100%-10%, and TDI_25%-25% all correlated significantly with flow (P < 0.001). TDI_10%-100%, TDI_100%-10%, and TDI_25%-25% showed, respectively, a correlation coefficient of 0.91, 0.91, and 0.97 in the anterior-posterior DSA projections (P < 0.001). In the lateral DSA projection, TDI_100%-10% showed a weaker correlation (r = 0.57; P = 0.03). Also in the oblique DSA projection, TDIs correlated significantly with flow.

CONCLUSIONS

TDI on DSA correlates significantly with flow. Although in vitro studies might overlook conditions that occur in patients, this method appears to correlate with the flow and could offer a semiquantitative method to evaluate the cerebral blood flow.

Quantitative assessment of changes in hemodynamics of the internal carotid artery after bypass surgery for moyamoya disease

OBJECTIVE Although intracranial vessel remodeling has been observed in moyamoya disease, concerns remain regarding the effect of bypass surgery on hemodynamic changes within the internal carotid artery (ICA). The authors aimed to quantify the surgical effect of bypass surgery on bilateral ICAs in moyamoya disease and to estimate pressure drop (PD) along the length of the ICA to predict surgical outcomes. METHODS Records of patients who underwent bypass surgery for treatment of moyamoya disease and in whom flow rates were obtained pre- and postsurgery by quantitative MR angiography were retrospectively reviewed. Quantitative MR angiography and computational fluid dynamics were applied to measure morphological and hemodynamic changes during pre- and postbypass procedures. The results for vessel diameter, volumetric flow, PD, and mean wall shear stress along the length of the ICA were analyzed. Subgroup analysis was performed for the circle of Willis (CoW) configurations. RESULTS Twenty-three patients were included. The PD in ICAs on the surgical side (surgical ICAs) decreased by 21.18% (SD ± 30.1%) and increased by 11.75% (SD ± 28.6%) in ICAs on the nonsurgical side (contralateral ICAs) (p = 0.001). When the PD in contralateral ICAs was compared between patients with a complete or incomplete CoW, the authors found that the PDI in the former group decreased by 2.45% and increased by 20.88% in the latter (p = 0.05). Regression tests revealed that a greater postoperative decrease in PD corresponded to shrinking of ICAs (R² = 0.22, p = 0.02). CONCLUSIONS PD may be used as a reliable biomechanical indicator for the assessment of surgical treatment outcomes. The vessel remodeling characteristics of contralateral ICA were related to CoW configurations.

Cerebral Arteriovenous Malformation Flow Is Associated With Venous Intimal Hyperplasia

BACKGROUND AND PURPOSE

The pathogenesis of venous intimal hyperplasia and venous outflow stenosis associated with cerebral arteriovenous malformation (AVM) draining veins is poorly understood. We sought to determine the relationship between maximum vein wall thickness and AVM flow.

METHODS

Patients who underwent AVM surgical resection and had flow measured before treatment using quantitative magnetic resonance angiography were retrospectively reviewed. Specimens were mounted on slides and stained with elastin special stain. Perinidal veins were identified, and maximum wall thickness was measured from digitized images. Relationship between maximum vein wall thickness and AVM flow was assessed.

RESULTS

Twenty-eight patients were included. Spearman correlation revealed a statistically significant relationship between maximum vein wall thickness and total AVM flow (ρ=+0.51; P=0.006), AVM flow per draining vein (ρ=+0.41; P=0.03), and mean intranidal vessel diameter (ρ=+0.39; P=0.04).

CONCLUSIONS

Maximum vein wall thickness increases with higher total AVM flow and AVM flow per draining vein. This finding implicates chronically high AVM inflow in venous intimal hyperplasia.

Validation of cerebral arteriovenous malformation hemodynamics assessed by DSA using quantitative magnetic resonance angiography: preliminary study

BACKGROUND

The hemodynamic evaluation of cerebral arteriovenous malformations (AVMs) using DSA has not been validated against true flow measurements.

OBJECTIVE

To validate AVM hemodynamics assessed by DSA using quantitative magnetic resonance angiography (QMRA).

MATERIALS AND METHODS

Patients seen at our institution between 2007 and 2016 with a supratentorial AVM and DSA and QMRA obtained before any treatment were retrospectively reviewed. DSA assessment of AVM flow comprised AVM arterial-to-venous time (A-Vt) and iFlow transit time. A-Vt was defined as the difference between peak contrast intensity in the cavernous internal carotid artery and peak contrast intensity in the draining vein. iFlow transit times were determined using syngo iFlow software. A-Vt and iFlow transit times were correlated with total AVM flow measured using QMRA and AVM angioarchitectural and clinical features.

RESULTS

33 patients (mean age 33 years) were included. Nine patients presented with hemorrhage. Mean AVM volume was 9.8 mL (range 0.3-57.7 mL). Both A-Vt (r=-0.47, p=0.01) and iFlow (r=-0.44, p=0.01) correlated significantly with total AVM flow. iFlow transit time was significantly shorter in patients who presented with seizure but A-Vt and iFlow did not vary with other AVM angioarchitectural features such as venous stenosis or hemorrhagic presentation.

CONCLUSIONS

A-Vt and iFlow transit times on DSA correlate with cerebral AVM flow measured using QMRA. Thus, these parameters may be used to indirectly estimate AVM flow before and after embolization during angiography in real time.

Quantitative assessment of parent vessel and distal intracranial hemodynamics following pipeline flow diversion

Background Pipeline embolization devices (PEDs) are commonly used for endovascular treatment of cerebral aneurysms but can be associated with delayed ipsilateral intraparenchymal hemorrhage. Although intra-aneurysmal hemodynamic changes have been studied, parent vessel and intracranial hemodynamics after PED use are unknown. We examine the impact of flow diversion on parent artery and distal intracranial hemodynamics. Method Patients with internal carotid cerebral aneurysms treated with PED who had flow volume rate, flow velocities, pulsatility index, resistance index, Lindegaard ratio, and wall shear stress (WSS) obtained after treatment using quantitative magnetic resonance angiography were reviewed. Means were compared between ipsilateral and contralateral internal carotid artery (ICA) and middle cerebral artery (MCA) using paired t tests. Results A total of 18 patients were included. Mean flow volume rate was lower in the ipsilateral versus contralateral ICA ( p = 0.04) but tended to be higher in the ipsilateral versus contralateral MCA ( p = 0.08). Lindegaard ratio was higher ipsilateral to the PED in diastole ( p = 0.05). Although there was no significant difference in flow velocities, pulsatility or resistance indices, and WSS, the two cases in our cohort with hemorrhagic complications did display significant changes in MCA flows and MCA WSS. Conclusion PED placement appears to alter the elasticity of the stented ICA segment, with lower flows in the ipsilateral versus contralateral ICA. Conversely, MCA flows and MCA WSS are higher in the ipsilateral MCA among patients with hemorrhage after PED placement, suggesting the role of disrupted distal hemodynamics in delayed ipsilateral intraparenchymal hemorrhage.

Novel imaging approaches to cerebrovascular disease

Imaging techniques available to the physician treating neurovascular disease have substantially grown over the past several decades. New techniques as well as advances in imaging modalities continuously develop and provide an extensive array of modalities to diagnose, characterize, and understand neurovascular pathology. Modern noninvasive neurovascular imaging is generally based on computed tomography (CT), magnetic resonance (MR) imaging, or nuclear imaging and includes CT angiography, CT perfusion, xenon-enhanced CT, single-photon emission CT, positron emission tomography, magnetic resonance angiography, MR perfusion, functional magnetic resonance imaging with global and regional blood oxygen level dependent imaging, and magnetic resonance angiography with the use of the noninvasive optional vessel analysis software (River Forest, Ill). In addition to a brief overview of the technique, this review article discusses the clinical indications, advantages, and disadvantages of each of those modalities.

Relationship of pulsatility and resistance indices to cerebral arteriovenous malformation angioarchitectural features and hemorrhage

The role that hemodynamics plays in the pathophysiology of cerebral arteriovenous malformation (AVM) hemorrhage remains unclear. Here, we examine the relationship of pulsatility and resistance indices to AVM angioarchitectural features and hemorrhage. Records of patients with cerebral AVMs evaluated at our institution between 2007-2014 and with flows obtained before treatment using quantitative magnetic resonance angiography (QMRA) were retrospectively reviewed. Flow volume rate and flow velocity were measured in primary arterial feeders and compared to their contralateral counterparts. Pulsatility index (PI)=[(systolic flow velocity-diastolic flow velocity)/mean flow velocity] and resistance index (RI)=[(systolic flow velocity-diastolic flow velocity)/systolic flow velocity] were calculated for each feeder and compared to the normal contralateral vessel. Relationships between PI, RI and AVM clinical and angioarchitectural features were assessed using linear regression. Seventy-two patients with a total of 101 feeder arteries were included. PI and RI were significantly lower in AVM arterial feeders compared to normal vessels, thereby resulting in significantly higher flow volume rates and flow velocities in feeder vessels. There was no significant association of PI and RI with hemorrhagic presentation, exclusive deep venous drainage, venous stenosis, single draining vein, or deep location. In conclusion, PI and RI can be measured using QMRA and are lower in AVM arterial feeders compared to normal vessels. Although we found no significant correlation between PI, RI, and AVM angioarchitectural characteristics thought to be associated with increased hemorrhage risk, future studies with larger sample sizes may better elucidate this relationship.

Correlation between angiographic transit times and neurological status on admission in patients with aneurysmal subarachnoid hemorrhage

OBJECT

The use of digital subtraction angiography (DSA) for semiquantitative cerebral blood flow(CBF) assessment is a new technique. The aim of this study was to determine whether patients with aneurysmal subarachnoid hemorrhage (aSAH) with higher Hunt and Hess grades also had higher angiographic contrast transit times (TTs) than patients with lower grades.

METHODS

A cohort of 30 patients with aSAH and 10 patients without aSAH was included. Relevant clinical information was collected. A method to measure DSA TTs by color-coding reconstructions from DSA contrast-intensity images was applied. Regions of interest (ROIs) were chosen over major cerebral vessels. The estimated TTs included time-to-peak from 0% to 100% (TTP0–100), TTP from 25% to 100% (TTP25–100), and TT from 100% to 10% (TT100–10) contrast intensities. Statistical analysis was used to compare TTs between Group A (Hunt and Hess Grade I-II), Group B (Hunt and Hess Grade III-IV), and the control group. The correlation coefficient was calculated between different ROIs in aSAH groups.

RESULTS

There was no difference in demographic factors between Group A (n = 10), Group B (n = 20), and the control group (n = 10). There was a strong correlation in all TTs between ROIs in the middle cerebral artery (M1, M2) and anterior cerebral artery (A1, A2). There was a statistically significant difference between Groups A and B in all TT parameters for ROIs. TT100–10 values in the control group were significantly lower than the values in Group B.

CONCLUSIONS

The DSA TTs showed significant correlation with Hunt and Hess grades. TT delays appear to be independent of increased intracranial pressure and may be an indicator of decreased CBF in patients with a higher Hunt and Hess grade. This method may serve as an indirect technique to assess relative CBF in the angiography suite.

Donor Selection in Flow Replacement Bypass Surgery for Cerebral Aneurysms: Quantitative Analysis of Long-term Native Donor Flow Sufficiency

BACKGROUND:

Graft selection in extracranial-intracranial bypass surgery for cerebral aneurysms has traditionally been based on clinical impression and operator preference. However, decision making can be optimized with a donor selection algorithm based on intraoperative flow data.

OBJECTIVE:

To present long-term follow-up and quantitative assessment of flow sufficiency for native donors selected in this manner.

METHODS:

Patients with bypass for anterior circulation intracranial aneurysms using only a native donor (superficial temporal artery) selected on the basis of an intraoperative flow algorithm over a 10-year period were retrospectively studied. Intracranial hemispheric and bypass flows were assessed preoperatively and postoperatively when available with quantitative magnetic resonance angiography.

RESULTS:

Twenty-two patients with flow data were included (median aneurysm size, 22 mm). The intraoperative flow offer (cut flow) of the superficial temporal artery was sufficient in these cases relative to the flow demand in the sacrificed vessel (59 vs 28 mL/min) to warrant its use. Bypass flow averaged 81 mL/min postoperatively (n = 19). Bypass flows were highest in the immediate postoperative period but remained stable between the intermediate and final follow-up (40 vs 52 mL/min; P = .39; n = 8). Mean ipsilateral hemisphere flows were maintained after bypass (299 vs 335 mL/min; P = .42; n = 7), and remained stable over intermediate and long-term follow-up. Ipsilateral hemispheric flows remained similar to contralateral flows at all time points.

CONCLUSION:

Despite a relative reduction in bypass flow over time, hemispheric flows were maintained, indicating that simple native donors can carry sufficient flow for territory demand long term when an intraoperative flow-based algorithm is used for donor selection.

Improvement in venous outflow following superior sagittal sinus decompression after a gunshot wound to the head: case report

The most commonly described indications for surgical management of closed depressed skull fractures are hematoma evacuation and repair of extensive cosmetic deformity. Venous sinus injury, which occurs in a subset of depressed skull fractures, is not typically listed as an indication for surgical treatment due to the potential for major venous hemorrhage associated with surgery near these structures. However, if patients exhibit signs and symptoms of intracranial hypertension and radiographic findings demonstrate sinus compromise, surgical elevation of the depressed skull fragments is indicated. The authors present the case of a 25-year-old woman with a depressed skull fracture secondary to a gunshot wound with symptomatic compromise in venous outflow of the posterior one-third of the superior sagittal sinus. The patient was treated with surgical decompression via bilateral craniectomy along with intracranial pressure-lowering medical therapy and had almost full resolution of her presenting symptoms with documented improvement in flow through the superior sagittal sinus. While the use of surgical treatment for these types of injuries is highly debated, the authors demonstrate here that safe, effective surgical management of these patients is possible and that surgical decompression should always be considered in the case of symptomatic venous sinus flow obstruction.

Changes in wall shear stress of cerebral arteriovenous malformation feeder arteries after embolization and surgery

BACKGROUND AND PURPOSE

Wall shear stress (WSS) has been implicated as an important stimulus for vascular remodeling. The purpose of this study is to measure WSS in AVM arterial feeders using quantitative magnetic resonance angiography pre- and post-embolization/surgery.

METHODS

Records of patients who underwent AVM embolization and surgical resection at our institution between 2007 and 2013 and had WSS, flow rate, and vessel diameter obtained pre- and post-treatment using quantitative magnetic resonance angiography were retrospectively reviewed. WSS was compared between the feeder and contralateral artery pre- and post-embolization/surgery.

RESULTS

Twenty-one patients were included (mean age 34 years, 19% hemorrhagic presentation), with Spetzler-Martin grades 1 to 4. WSS, blood flow, and vessel diameter were assessed in a total of 51 feeder arteries. At baseline, mean WSS was significantly higher compared with the contralateral vessel (29.7±12.0 dynes/cm(2) versus 23.3±11.0 dynes/cm(2); P=0.007). After embolization (23.0 dynes/cm(2) versus 22.5 dynes/cm(2); P=0.78) and surgery (17.9 dynes/cm(2) versus 23.2 dynes/cm(2); P=0.09), WSS was not significantly different than in the contralateral vessel. Reduced WSS post-embolization corresponded to significantly decreased flow (338.1 mL/min versus 170.3 mL/min; P<0.001) and smaller vessel diameter (3.7 mm versus 3.5 mm; P=0.01).

CONCLUSIONS

Enlargement of cerebral AVM arterial feeders is insufficient to compensate for increased blood flow, creating high WSS. After treatment, flow diminishes and so WSS and vessel diameter concomitantly decrease. Thus, WSS plays a pivotal role in vascular remodeling that may be exploited to monitor AVM response to treatment or understand other high-flow vascular pathologies.

Quantitative assessment of changes in cerebral arteriovenous malformation hemodynamics after embolization

BACKGROUND AND PURPOSE

Embolization reduces flow in arteriovenous malformations (AVMs) before surgical resection, but achievement of this goal is determined subjectively from angiograms. Here, we quantify effects of embolization on AVM flow.

METHODS

Records of patients who underwent AVM embolization at our institution between 2007 and 2013 and had flow rates obtained pre- and postembolization using quantitative magnetic resonance angiography were retrospectively reviewed. Total flow was estimated as aggregate flow within primary arterial feeders or flow in single draining veins.

RESULTS

Twenty-one patients were included (mean age 35 years, 24% hemorrhagic presentation) with Spetzler-Martin grades 1 to 4. Fifty-four total embolization sessions were performed. The mean AVM flow was 403.4±262.4 mL/min at baseline, 285.3±246.4 mL/min after single session (29% drop, P<0.001), and 102.0±103.3 mL/min after all sessions of embolization (75% drop, P<0.001). Total number of pedicles embolized (P<0.001) and embolization of an intranidal fistula during any session (P=0.002) were significantly associated with total decreased flow postembolization. On multivariate analysis, total pedicles embolized was predictive of total flow drop (P<0.001). However, pedicles embolized per session did not correlate with flow drop related to that session (P=0.44).

CONCLUSIONS

AVM flow changes after embolization can be measured using quantitative magnetic resonance angiography. The total number of pedicles embolized after multiple embolization sessions was predictive of final flow, indicating this parameter is the best angiographic marker of a hemodynamically successful intervention. The number of pedicles embolized per session, however, did not correlate with flow drop in that session, likely because of flow redistribution after partial embolization.

Effect of age and vascular anatomy on blood flow in major cerebral vessels

Measurement of volume flow rates in major cerebral vessels can be used to evaluate the hemodynamic effects of cerebrovascular disease. However, both age and vascular anatomy can affect flow rates independent of disease. We prospectively evaluated 325 healthy adult volunteers using phase contrast quantitative magnetic resonance angiography to characterize these effects on cerebral vessel flow rates and establish clinically useful normative reference values. Flows were measured in the major intracranial and extracranial vessels. The cohort ranged from 18 to 84 years old, with 157 (48%) females. All individual vessel flows and total cerebral blood flow (TCBF) declined with age, at 2.6 mL/minute per year for TCBF. Basilar artery (BA) flow was significantly decreased in individuals with one or both fetal posterior cerebral arteries (PCAs). Internal carotid artery flows were significantly higher with a fetal PCA and decreased with a hypoplastic anterior cerebral artery. Indexing vessel flows to TCBF neutralized the age effect, but anatomic variations continued to impact indexed flow in the BA and internal carotid artery. Variability in normative flow ranges were reduced in distal vessels and by examining regional flows. Cerebral vessel flows are affected by age and cerebrovascular anatomy, which has important implications for interpretation of flows in the disease state.

Intracranial Blood Flow Changes After Extracranial Carotid Artery Stenting

BACKGROUND:

Carotid artery stenting is an endovascular treatment option for patients with extracranial carotid stenosis. However, intracranial blood flow changes following stenting have not been established.

OBJECTIVE:

To determine the effects of stenting on intracranial blood flow.

METHODS:

Records of patients who underwent stenting at our institution between 2004 and 2012 and had flow rates obtained pre- and poststenting by the use of quantitative magnetic resonance angiography were retrospectively reviewed. Percentage stenosis, stenosis length, and minimum vessel diameter were measured from cerebral angiography images.

RESULTS:

Eighteen patients were included. Mean age was 65 years with 67% presenting with symptomatic stenosis. Degree of stenosis ranged from 60% to 90%. Internal carotid artery (ICA) mean flow improved significantly poststenting from 174.9 ± 83.6 mL/min to 250.7 ± 91.2 mL/min (P = .011). Ipsilateral middle cerebral artery (MCA) flow, however, was not significantly altered poststenting (107.8 ± 41.6 mL/min vs 114.3 ± 36.3 mL/min; P = .28). Univariate analysis revealed that improved minimum vessel diameter after stenting, but not percentage stenosis (P = .18) or stenosis length (P = .45), is significantly associated with increased ICA flow (P = .02). However, improved percentage stenosis, stenosis length, minimum vessel diameter, and ICA flow poststenting were not significantly associated with increased MCA flow (P = .64, .38, .13, .37, respectively).

CONCLUSION:

ICA flow was compromised at baseline, improving 43% on average poststenting. Increased minimum vessel diameter was the factor most significantly associated with increased flow. Conversely, MCA flow was not significantly compromised at baseline nor altered after stenting, suggesting compensatory intracranial collateral supply prestenting that redistributes following ICA revascularization.

Combined Direct and Indirect Bypass for Moyamoya

BACKGROUND:

The optimal revascularization strategy for symptomatic adult moyamoya remains controversial. Whereas direct bypass offers immediate revascularization, indirect bypass can effectively induce collaterals over time.

OBJECTIVE:

Using angiography and quantitative magnetic resonance angiography, we examined the relative contributions of direct and indirect bypass in moyamoya patients after combined direct superficial temporal artery-to-middle cerebral artery (STA-MCA) bypass and indirect encephaloduroarteriosynangiosis (EDAS).

METHODS:

A retrospective review of moyamoya patients undergoing combined STA-MCA bypass and EDAS was conducted, excluding pediatric patients and hemorrhagic presentation. Patients with quantitative magnetic resonance angiography measurements of the direct bypass immediately and &gt; 6 months postoperatively were included. Angiographic follow-up, when available, was used to assess EDAS collaterals at similar time intervals.

RESULTS:

Of 16 hemispheres in 13 patients, 11 (69%) demonstrated a significant (&gt; 50%) decline in direct bypass flow at &gt; 6 months compared with baseline, averaging a drop from 99 ± 35 to12 ± 7 mL/min. Conversely, angiography in these hemispheres demonstrated prominent indirect collaterals, in concert with shrinkage of the STA graft. Decline in flow was apparent at a median of 9 months but was evident as early as 2 to 3 months.

CONCLUSION:

In this small cohort, a reciprocal relationship between direct STA bypass flow and indirect EDAS collaterals frequently occurred. This substantiates the notion that combined direct/indirect bypass can provide temporally complementary revascularization.