The Utility of Quantitative Magnetic Resonance Angiography in the Assessment of Intracranial In-Stent Stenosis

Quantitative magnetic resonance angiography as an alternative imaging technique in the assessment of cerebral vasospasm after subarachnoid hemorrhage

INTRODUCTION

The major mechanism of morbidity of delayed cerebral ischemia after subarachnoid hemorrhage (SAH) is considered to be severe vasospasm. Quantitative MRA (QMRA) provides direct measurements of vessel-specific volumetric blood flow and may permit a clinically relevant assessment of the risk of ischemia secondary to cerebral vasospasm.

PURPOSE

To evaluate the utility of QMRA as an alternative imaging technique for the assessment of cerebral vasospasm after SAH.

METHODS

QMRA volumetric flow rates of the anterior cerebral artery (ACA), middle cerebral artery (MCA), and posterior cerebral artery (PCA) were compared with vessel diameters on catheter-based angiography. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of QMRA for detecting cerebral vasospasm was determined by receiver-operating characteristic curves. Spearman correlation coefficients were calculated for QMRA flow versus angiographic vessel diameter.

RESULTS

Sixty-six vessels (10 patients) were evaluated with QMRA and catheter-based angiography. The median percent QMRA flow of all vessels with angiographic vasospasm (55.0%, IQR 34.3-71.6%) was significantly lower than the median percent QMRA flow of vessels without vasospasm (91.4%, IQR 81.4-100.4%) (p < 0.001). Angiographic vasospasm reduced QMRA-assessed flow by 23 ± 5 (p = 0.018), 95 ± 12 (p = 0.042), and 16 ± 4 mL/min (p = 0.153) in the ACA, MCA, and PCA, respectively, compared to vessels without angiographic vasospasm. The sensitivity, specificity, PPV, and NPV of QMRA for the discrimination of cerebral vasospasm was 84%, 72%, 84%, and 72%, respectively, for angiographic vasospasm >25% and 91%, 60%, 87%, and 69%, respectively, for angiographic vasospasm >50%. The Spearman correlation indicated a significant association between QMRA flows and vessel diameters (rs = 0.71, p < 0.001).

CONCLUSION

Reduction in QMRA flow correlates with angiographic vessel narrowing and may be useful as a non-invasive imaging modality for the detection of cerebral vasospasm after SAH.

Selective endovascular treatment of cervical arterial dissection using quantitative magnetic resonance angiography

INTRODUCTION

The role of endovascular treatment in cervical artery dissection (CAD) is equivocal. This study compared cerebral blood flow in CAD between medically and endovascularly treated patients using quantitative magnetic resonance angiography (QMRA).

METHODS

Retrospective chart review was completed for patients with CAD. Inclusion criteria were adults (>18 years) with diagnosis of dissection of the internal carotid artery or vertebral artery who received QMRA. The cases were reviewed for clinical presentation, diagnosis, management, and imaging, and in particular, patients who underwent endovascular treatment were evaluated.

RESULTS

Forty-one patients were included, 46.3% female and mean age 46.0+/- 11.9 years. 21 patients (51.2%) had contralateral (ICA) dissections while 19 (46.3%) had vertebral artery (VA) dissections, and 1 had both involved. Five patients underwent stenting, angioplasty, or both. Baseline characteristics between patients who underwent medical versus endovascular treatment were similar, although patients undergoing stenting/angioplasty were more likely to have diabetes (p = 0.015) and prior anticoagulation use (p = 0.007). All endovascular patients demonstrated ischemia on MRI versus 53.1% of those undergoing medical management (p = 0.047). Comparing ipsilateral vessel flow over time in these two patient groups showed those who underwent stenting or angioplasty had lower baseline flows, albeit non-significant (p = 0.629). Patients who underwent endovascular treatment had lower distal flow compared to the medical management group.

CONCLUSION

This study represents the first to assess vessel flow using QMRA in patients who underwent endovascular treatment of CAD. In combination with progressive symptoms, QMRA may serve as a useful adjunct in the selection of patients for endovascular intervention in arterial dissections.

Epidemiology, Pathophysiology, and Imaging of Atherosclerotic Intracranial Disease

Intracranial atherosclerotic disease (ICAD) is one of the most common causes of stroke worldwide. Among people with stroke, those of East Asia descent and non-White populations in the United States have a higher burden of ICAD-related stroke compared with Whites of European descent. Disparities in the prevalence of asymptomatic ICAD are less marked than with symptomatic ICAD. In addition to stroke, ICAD increases the risk of dementia and cognitive decline, magnifying ICAD societal burden. The risk of stroke recurrence among patients with ICAD-related stroke is the highest among those with confirmed stroke and stenosis ≥70%. In fact, the 1-year recurrent stroke rate of >20% among those with stenosis >70% is one of the highest rates among common causes of stroke. The mechanisms by which ICAD causes stroke include plaque rupture with in situ thrombosis and occlusion or artery-to-artery embolization, hemodynamic injury, and branch occlusive disease. The risk of stroke recurrence varies by the presumed underlying mechanism of stroke, but whether techniques such as quantitative magnetic resonance angiography, computed tomographic angiography, magnetic resonance perfusion, or transcranial Doppler can help with risk stratification beyond the degree of stenosis is less clear. The diagnosis of ICAD is heavily reliant on lumen-based studies, such as computed tomographic angiography, magnetic resonance angiography, or digital subtraction angiography, but newer technologies, such as high-resolution vessel wall magnetic resonance imaging, can help distinguish ICAD from stenosing arteriopathies.

Multimodal imaging approach for the diagnosis of intracranial atherosclerotic disease (ICAD): Basic principles, current and future perspectives

PURPOSE

To review the different imaging modalities utilized in the diagnosis of Intracranial Atherosclerotic Disease (ICAD) including their latest development and relevance in management of ICAD.

METHODS

A review of the literature was conducted through a search in google scholar, PubMed/Medline, EMBASE, Scopus, clinical trials.gov and the Cochrane Library. Search terms included, "imaging modalities in ICAD," "ICAD diagnostic," "Neuroimaging of ICAD," "Evaluation of ICAD". A summary and comparison of each modality's basic principles, advantages and disadvantages were included.

RESULTS

A total of 144 articles were identified and reviewed. The most common imaging used in ICAD diagnoses were DSA, CTA, MRA and TCD. They all had proven accuracy, their own benefits, and limitations. Newer modalities such as VWI, IVUS, OCT, PWI and CFD provide more detailed information regarding the vessel walls, plaque characteristics, and flow dynamics, which play a tremendous role in treatment guidance. In certain clinical scenarios, using more than one modality has been shown to be helpful in ICAD identification. The rapidly evolving software related to imaging studies, such as virtual histology, are very promising for the diagnostic and management of ICAD.

CONCLUSIONS

ICAD is a common cause of recurrent ischemic stroke. Its management can be both medical and/or procedural. Many different imaging modalities are used in its diagnosis. In certain clinical scenario, a combination of two more modalities can be critical in the management of ICAD. We expect that continuous development of imaging technique will lead to individualized and less invasive management with adequate outcome.

Intracranial atherosclerosis: Review of imaging features and advances in diagnostics

Intracranial atherosclerotic disease is one of the leading causes of ischemic strokes and poses a moderate risk of recurrence. Diagnosis is currently limited to stenosis on luminal imaging, which likely underestimates the true prevalence of the disease. Detection of non-stenosing intracranial atherosclerosis is important in order to optimize secondary stroke prevention strategies. This review collates findings from the early seminal trials and the latest studies in advanced radiological techniques that characterize symptomatic intracranial atherosclerotic disease across various imaging modalities. While computed tomography angiography (CTA) and magnetic resonance angiography (MRA) comprise diagnostic mainstays in identifying stenotic changes secondary to atherosclerosis, emerging techniques such as high-resolution MRA, quantitative MRA, and computational fluid dynamics may reveal a myriad of other underlying pathophysiological mechanisms.

Utility of quantitative magnetic resonance angiography and non-invasive optimal vessel analysis for identification of complications and long-term hemodynamic changes in post-pipeline embolization patients

INTRODUCTION

Quantitative magnetic resonance angiography and non-invasive optimal vessel analysis serve as powerful tools to collect and analyze hemodynamic data from pipeline embolization patients. At our institution, patients receive post-embolization quantitative magnetic resonance angiography within 24 h of treatment and within 6 months for follow-up to evaluate pipeline patency. Here, we aim to elucidate the long-term hemodynamic changes following pipeline embolization device placement and report two cases in which in-stent stenosis was detected.

METHODS

Medical records of patients who underwent pipeline embolization device placement for an internal carotid artery aneurysm between 2017 and 2019 were reviewed. Patients who received post-procedure NOVA and follow-up NOVA were included in the study (n = 32). Location and size of aneurysm, number of pipeline embolization device deployed, and complications were collected along with the non-invasive optimal vessel analysis report (flow volume rate (ml/min), mean, systolic, and diastolic flow velocities (cm/s), and vessel diameter (mm)). Internal carotid artery vessel flow rate was measured proximal to the pipeline embolization device. Derivations of hemodynamic parameters (pulsatility index, Lindegaard ratio, and wall shear stress) were calculated.

RESULTS

The middle cerebral artery mean and diastolic flow velocities were significantly lower on the follow-up NOVA compared to the post-procedure NOVA. Moreover, follow-up NOVA demonstrated lower middle cerebral artery wall shear stress on the side with flow diversion compared to the post-procedure NOVA. In-stent stenosis, requiring intervention, was detected in two patients on follow-up NOVA. One patient had a successful balloon angioplasty of the stented internal carotid artery that resolved her stenosis. However, the second patient developed progressive stenosis and expired despite intervention.

CONCLUSION

Long-term hemodynamic adaptations post-pipeline embolization device demonstrate decreased wall shear stress and decreased mean and diastolic flow velocities in the distal middle cerebral artery, which suggest decreasing velocity of blood flow with endothelialization of the device. Furthermore, follow-up NOVA is a useful tool for detecting potential flow-related complications such as in-stent stenosis.

Quantitative Magnetic Resonance Angiography Fails to Screen In-Stent Restenosis but Predicts Good Long-Term Outcome

Wingspan stent in the setting of symptomatic intracranial atherosclerotic disease (ICAD) has shown to be associated with in-stent restenosis (ISR). Conventional angiography is typically used to detect ISR, but quantitative magnetic resonance angiography (QMRA), a non-invasive measure of blood hemodynamics, has also been used to screen for ISR. This report highlights a case where QMRA failed to screen for ISR in a patient who received a Wingspan stent for symptomatic intracranial vertebral artery stenosis but predicted good long-term outcome. The patient remained asymptomatic and had robust vertebrobasilar flow at long-term follow-up despite developing ISR.

Blood Flow Volume Measurement in Cervical and Intracranial Arteries using Quantitative Magnetic Resonance Angiography and Duplex Sonography (Bocaccia) - A Prospective Observational Study

PURPOSE

 Cerebral blood flow volume is an important factor for the accurate diagnosis of neurovascular diseases and treatment indication. This study aims to assess correlations of blood flow volume measurements in cervical and intracranial arteries between duplex sonography and quantitative magnetic resonance angiography (qMRA).

MATERIALS AND METHODS

 Consecutive patients with suspicion of cerebral vascular pathology underwent qMRA and duplex sonography of cervical and intracranial arteries with measurement of blood flow volume in bilateral common (CCA), internal (ICA) and external carotid arteries, vertebral and basilar arteries, middle, anterior, posterior cerebral and posterior communicating arteries using 2 different ultrasound machines. Ten patients underwent all examinations twice. Correlations between blood flow volume measurements were evaluated using Spearman's correlation coefficient and inter-class correlation coefficient (ICC).

RESULTS

 In total, 21 subjects (15 males, mean age: 56.3 ± 6.2 years) were included in the study. Duplex sonography inter-investigator correlation was excellent (ICC = 0.972, p < 0.0001) as well as intra-investigator correlations of both qMRA and duplex sonography (ICC ˃ 0.990, p < 0.0001). Mostly high correlations were recorded between qMRA and duplex sonography in particular cervical arteries but only low to moderate correlations were obtained for intracranial arteries. The mean differences between blood flow volume measurements were 10.9 ± 8.1 % in the CCA and its branches when using qMRA and 15.0 ± 11.9 % when using duplex sonography, 13.5 ± 11.8 %/35.4 ± 34.2 % in the ICA siphon and its branches when using qMRA/duplex sonography, and 24.1 ± 19.7 %/44.9 ± 44.0 % in both vertebral arteries and the basilar artery when using qMRA/duplex sonography.

CONCLUSION

 Duplex sonography as well as qMRA allow for highly reproducible measurement of blood flow volume in cervical and intracranial arteries in routine clinical practice.

Carotid Revascularization and Its Effect on Cognitive Function: A Prospective Nonrandomized Multicenter Clinical Study

BACKGROUND

There is conflicting data on the effect of carotid revascularization on cognitive function.

OBJECTIVE

To examine cerebral blood flow and cognitive function after carotid revascularization.

METHODS

Patients with unilateral, asymptomatic hemodynamically significant carotid artery stenosis (80% by computed tomography angiography or magnetic resonance angiography) were eligible. Cerebral blood flow was measured preoperatively and 1 month postoperatively using quantitative phase contrast magnetic resonance angiography. Preoperative flow impairment was defined as ipsilateral flow at least 20% less than contralateral flow (ie, an ipsilateral and/or contralateral flow ratio ≤0.8). Significant improvement in blood flow was defined as at least a 0.15 increase in flow ratio from pre- to postoperative. A control group was managed medically. Four cognitive domains were assessed at baseline, 1 month, and 6-12 months postoperatively.

RESULTS

Seventy-five patients were enrolled at 6 sites; 53 carotid endarterectomy, 11 carotid artery stenting, and 11 medical management only controls. Preoperative Trails B scores were similar between groups. Revascularization was associated with significant improvement in executive function (Trials B) while no improvement was observed in controls (P = .007). Of patients with improvement in middle cerebral artery (MCA) flow, 90% had improved Trails B scores compared to 46.5% of patients without MCA flow improvement (P = .01). Greater absolute improvement in mean Trails B scores was observed in patients with MCA flow improvement compared to those without (48 seconds versus 24.7 seconds, P = .001).

CONCLUSIONS

In a cohort of patient with asymptomatic carotid stenosis, improvement in MCA flow following carotid revascularization is associated with improvement in executive functioning.

Long Term Outcome of In-Stent Stenosis after Stent Assisted Coil Embolization for Cerebral Aneurysm

Objective

The objective of this study was to evaluatelong-term radiologic prognosis and characteristics of in-stent stenosis (ISS) after stent assisted coiling (SAC) for cerebral aneurysm and analyze its risk factors.

Methods

Radiological records of 362 cases of SAC during 10 years were retrospectively reviewed. Patients were included in this study if they had follow-up angiogram using catheter selected angiography at least twice. All subjected were followed up from 12 months to over 30 months. Of 120 patients, 123 aneurysms were enrolled. Patient data including age, sex, aneurysm size, neck size, procedural complication, kinds of stent, ISS associated symptom, ruptured state, location of ISS, degree of ISS, radiologic prognosis of ISS, follow-up period of time, and medical comorbidities such as hypertension, diabetes mellitus (DM), dyslipidemia, and smoking were collected.Statistical comparisons of group clinical characteristics were conducted for the total population.

Results

Among 123 casesof aneurysm, 22 cases (17.9%) of ISS were revealed on follow-up angiography. Multiple stenting was performed in three cases and intra-procedural rupture occurred in two cases. Most cases were asymptomatic and symptomatic stenosis was identified in only one case. Sixteen cases were ruptured aneurysm. Mild stenosis was observed in 11 cases. Moderate stenosis was found in eight cases and severe stenosis was identified in three cases. Mean timing of identification of ISS was 8.90 months. The most common type was proximal type. Most cases were improved or not changed on follow-up angiography. Only one case was aggravated from mild stenosis to occlusion of parent artery. Mean follow-up period was 44.3 months. We compared risk factors and characteristic between ISS group and non-ISS group using univariate analysis. Multiple stenting was performed for three cases (13.6%) of the ISS group and four cases (4.0%) of the non-ISS group, showing no statistical difference between the two groups (p=0.108). Additionally, the proportion of patients who had more than two risk factors among four medical risk factors (hypertension, DM, dyslipidemia, and smoking) was higher in the ISS group than that in the non-ISS group, the difference between the two was not statistically significant either (31.8% vs. 12.9%, p=0.05).

Conclusion

Clinical course and long-term prognosis of ISS might be benign. Most cases of ISS could be improved or not aggravated. Control of medical co-morbidity might be important. To the best of our knowledge, our study had more cases with longer follow-up period of time than other reports.

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.

Intracranial atherosclerotic disease

Intracranial atherosclerosis (ICAS) is a progressive pathological process that causes progressive stenosis and cerebral hypoperfusion and is a major cause of stroke occurrence and recurrence around the world. Multiple factors contribute to the development of ICAS. Angiography imaging techniques can improve the diagnosis of and the selection of appropriate treatment regimens for ICAS. Neither aggressive medication nor endovascular interventions can eradicate stroke recurrence in patients with ICAS. Non-pharmacological therapies such as remote ischemic conditioning and hypothermia are emerging. Comprehensive therapy with medication in combination with endovascular intervention and/or non-pharmacological treatment may be a potential strategy for ICAS treatment in the future. We summarized the epidemiology, pathophysiological mechanisms, risk factors, biomarkers, imaging and management of ICAS.

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.

Measuring Cerebral Blood Flow in Moyamoya Angiopathy by Quantitative Magnetic Resonance Angiography Noninvasive Optimal Vessel Analysis

BACKGROUND

Moyamoya disease causes progressive occlusion of the supraclinoidal internal carotid artery, and middle, anterior, and less frequently the posterior cerebral arteries, carrying the risk of stroke. Blood flow is often partially reconstituted by compensatory moyamoya collaterals and sometimes the posterior circulation. Cerebral revascularization can further augment blood flow. These changes to blood flow within the cerebral vessels, however, are not well characterized.

OBJECTIVE

To evaluate blood flow changes resulting from the disease process and revascularization surgery using quantitative magnetic resonance angiography with noninvasive optimal vessel analysis (NOVA).

METHODS

We retrospectively analyzed 190 preoperative and postoperative imaging scans in 66 moyamoya patients after revascularization surgery. Images were analyzed for blood flow using NOVA and compared with preoperative angiographic staging and postoperative blood flow. Blood flow rates within superficial temporal artery grafts were compared based on angiographic evidence of patency.

RESULTS

Diseased vessels had lower blood flow, correlating with angiographic staging. Flow in posterior cererbal and basilar arteries increased with disease severity, particularly when both the anterior and middle cerebral arteries were occluded. Basilar artery flow and ipsilateral internal carotid artery flow decreased after surgery. Flow rates were different between angiographically robust and poor direct bypass grafts, as well as between robust and patent grafts.

CONCLUSION

Preoperative changes in cerebral vessel flow as measured by NOVA correlated with angiographic disease progression. NOVA demonstrated that preoperative augmentation of the posterior circulation decreased after surgery. This report is the first to quantify the shift in collateral supply from the posterior circulation to the bypass graft.

Intracranial atherosclerosis: From anatomy to pathophysiology

Background

Intracranial atherosclerotic stenosis is an important etiology subtype of ischemic stroke. Stenosis severity was thought to be the main reference index for clinical treatment and research. However, stenosis could not reflect the ischemia risk completely, instead the hemodynamic state across the lesion, the extent of collateral circulation, and perfusion impairment downstream the stenosis are more important.

Aims

We write this review aimed to summarize novel angiographic methods applied in the evaluation of functional severity of ICAS, and commented on their limitations and prospects in future research.

Summary of review

The main methods to estimate cerebral blood flow including fractional flow assessed by signal intensity ratio, computational fluid dynamics analysis or pressure wire, quantitative magnetic resonance angiography. Fractional flow as a series cerebral hemodynamic parameters may reflect the status of collateral circulation and cerebral blood flow. But the accuracy of the methods was not validated. The method to calculate fractional flow reserve in cardiovascular disease cannot duplicate in cerebrovascular disease. Fractional flow measurement by floating a pressure guidewire across the intracranial stenosis was technically feasible and safe. In the future researches, a non-invasive method should be established to identify high-risk intracranial lesions and may help in decision-making.

Conclusions

The relationship between stenosis and cerebral blood flow was individualized. Cerebral hemodynamic criteria should be used to screen patients to endovascular treatment, which will optimize the diagnosis and treatment strategies for patients with symptomatic intracranial artery stenosis.

In Vivo Assessment of the Impact of Regional Intracranial Atherosclerotic Lesions on Brain Arterial 3D Hemodynamics

BACKGROUND AND PURPOSE

Intracranial atherosclerosis induces hemodynamic disturbance, which is not well-characterized, particularly in cerebral flow redistribution. We aimed to characterize the impact of regional stenotic lesions on intracranial hemodynamics by using 4D flow MR imaging.

MATERIALS AND METHODS

4D flow MR imaging was performed in 22 symptomatic patients (mean age, 68.4 ± 14.2 years) with intracranial stenosis (ICA, n = 7; MCA, n = 9; basilar artery, n = 6) and 10 age-appropriate healthy volunteers (mean age, 60.7 ± 8.1 years). 3D blood flow patterns were visualized by using time-integrated pathlines. Blood flow and peak velocity asymmetry indices were compared between patients and healthy volunteers in 4 prespecified arteries: ICAs, MCAs, and anterior/posterior cerebral arteries.

RESULTS

3D blood flow pathlines demonstrated flow redistribution across cerebral arteries in patients with unilateral intracranial stenosis. For patients with ICA stenosis compared with healthy volunteers, significantly lower flow and peak velocities were identified in the ipsilateral ICA (P = .001 and P = .001) and MCA (P < .001 and P = .001), but higher flow, in the ipsilateral PCA (P < .001). For patients with MCA stenosis, significantly lower flow and peak velocities were observed in the ipsilateral ICA (P = .009 and P = .045) and MCA (P < .001 and P = .005), but significantly higher flow was found in the ipsilateral posterior cerebral artery (P = .014) and anterior cerebral artery (P = .006). The asymmetry indices were not significantly different between patients with basilar artery stenosis and the healthy volunteers.

CONCLUSIONS

Regional intracranial atherosclerotic lesions not only alter distal arterial flow but also significantly affect ipsilateral collateral arterial hemodynamics.

Influence of different reconstruction parameters in the visualization of intracranial stents using C-arm flat panel CT angiography: experience in an animal model

BACKGROUND

C-arm flat panel computed tomography angiography (CA-CTA) is a relatively new imaging modality. Consequently, knowledge about postprocessing parameters and their influence on image quality is still limited, especially for the visualization of implanted microstents.

PURPOSE

To optimize reconstruction parameters by evaluating the influence of these different parameters for CA-CTA visualization of microstents in an animal model.

MATERIAL AND METHODS

Eleven microstents were implanted within the left common carotid artery of 11 New Zealand white rabbits. Both CA-CTA, using intra-venous delivery of contrast material, and conventional digital subtraction angiography (DSA) was performed. CA-CTA datasets were reconstructed using three different image characteristics (normal, sharp, smooth). Two experienced neuroradiologists evaluated the image quality and performed measurements of inner and outer stent diameters as well as measurements of the lumen area.

RESULTS

Stent deployment was performed successfully in all animals. Inter-observer correlation coefficient for all measurements was high (r = 0.87-0.92). Lumen area and inner stent diameter were significantly smaller in image characteristic "smooth" (P < 0.01) than in "sharp" and "normal". Outer stent diameter was larger in "smooth" than in "sharp" and "normal" (P < 0.01). Stent strut size was significantly wider using image characteristic "smooth". "Sharp" and "normal" compared best to DSA, with "sharp" providing the closest match to DSA measurements, with the trade-off of significantly more noise than in the "normal" reconstructions.

CONCLUSION

The use of different image characteristics in the postprocessing of CA-CTA datasets has an influence on the visualization of implanted stents. Image characteristic "sharp" and "normal" compared best to DSA.

MR derived volumetric flow rate waveforms of internal carotid artery in patients treated for unruptured intracranial aneurysms by flow diversion technique

Little is known about the hemodynamic disturbances induced by the cerebral aneurysms in the parent artery and the effect of flow diverter stents (FDS) on these latter. A better understanding of the aneurysm-parent vessel complex relationship may aid our understanding of this disease and to optimize its treatment. The ability of volumetric flow rate (VFR) waveform to reflect the arterial compliance modifications is well known. By analyzing the VFR waveform and the pulsatility in the parent vessel, this study aimed to test the hypotheses that (1) intracranial aneurysms might disrupt the blood flow of the parent vessel and (2) the treatment by FDS might have measurable corrective effect on these changes. Ten patients followed for unruptured intracranial aneurysms treated by FDS and ten healthy volunteers as control group were included in this study. Two-dimensional quantitative phase-contrast magnetic resonance imaging (MRI) was performed on each patient on the ICA artery upstream and downstream to the aneurysm, and on each volunteer at similar locations. The aneurysms altered significantly the parent vessel pulsatility and this effect was correlated to their volume. The aneurysms treatment by FDS allowed for the restoration of a normally modulated flow and pulsatility correction in the parent vessel.

Long-term radiographic results of stent-assisted embolization of cerebral aneurysms

BACKGROUND

Aneurysmal subarachnoid hemorrhage is a disabling disease. Endovascular coiling provides minimally invasive, effective, and safe treatment of both ruptured and unruptured intracranial aneurysms. Intracranial stents have improved the endovascular treatment of complex aneurysms, but the long-term durability of this treatment modality needs clarification.

OBJECTIVE

To elucidate the long-term success of intracranial stent use in the treatment of aneurysms.

METHODS

Four hundred ten patients were treated with stent-assisted endovascular management of 464 aneurysms. Treatment of 363 small aneurysms, 88 large aneurysms, and 13 giant aneurysms was analyzed with respect to both long-term anatomic results with digital subtraction angiography and magnetic resonance angiography over the follow-up period.

RESULTS

The 6-month angiographic results of 387 aneurysm treatments revealed complete aneurysm occlusion in 282 (72.9%), residual aneurysm neck in 50 (12.9%), and residual aneurysm filling in 55 (14.2%). Long-term radiographic follow-up, performed in 262 patients (mean, 3.63 years), showed significant recurrence of only 3 aneurysms after 6-month follow-up imaging. Forty-eight aneurysms (11.9%) were considered radiographic failures during the follow-up period.

CONCLUSION

The aneurysm recurrence rate after stent-assisted embolization in this series was similar to published data using only coil embolization for the period between treatment and the initial follow-up imaging. For aneurysms that do not initially recur, the presented data suggest improved durability in the subsequent long-term follow-up period.

ABBREVIATIONS

DSA, digital subtraction angiographyMRA, magnetic resonance angiography.

Endovascular treatment of symptomatic intracranial atheromatous stenosis: a single center study of 21 consecutive cases

OBJECTIVES

This retrospective single-center study evaluated the technical success as well as the periprocedural and long-term complications of angioplasty with stenting of symptomatic intracranial atheromatous stenosis.

PATIENTS AND METHODS

From January 2005 to December 2010, 21 patients were treated by angioplasty with stent implantation for symptomatic atheromatous intracranial stenosis greater or equal to 50% at least 7 days after a stroke.

RESULTS

The median population age was 65 years (range: 41-88 years), and 76% (16/21) of the candidates had a history of transient ischemic attack (TIA) or stroke before the event qualifying them for an endovascular procedure. In addition, 86% (18/21) were taking antithrombotic medication at the time of the qualifying event. Technical success was obtained in all cases. The periprocedural stroke or death rate was 9.5% (2/21), and there was no other stroke or death after 30 days during the mean follow-up of 1.4 years.

CONCLUSION

Endovascular treatment of symptomatic intracranial atherothrombotic stenosis can lead to severe complications, particularly during the periprocedural period, but it also represents the only alternative treatment for patients who fail with medical therapy. Future studies need to focus on improvement of periprocedural complications. Essentially, this should include more rigorous selection of candidates as well as a better understanding of the pathophysiological mechanism(s) of the ischemic phenomenon related to stenosis.

4D phase contrast flow imaging for in-stent flow visualization and assessment of stent patency in peripheral vascular stents--a phantom study

PURPOSE

4D phase contrast flow imaging is increasingly used to study the hemodynamics in various vascular territories and pathologies. The aim of this study was to assess the feasibility and validity of MRI based 4D phase contrast flow imaging for the evaluation of in-stent blood flow in 17 commonly used peripheral stents.

MATERIALS AND METHODS

17 different peripheral stents were implanted into a MR compatible flow phantom. In-stent visibility, maximal velocity and flow visualization were assessed and estimates of in-stent patency obtained from 4D phase contrast flow data sets were compared to a conventional 3D contrast-enhanced magnetic resonance angiography (CE-MRA) as well as 2D PC flow measurements.

RESULTS

In all but 3 of the tested stents time-resolved 3D particle traces could be visualized inside the stent lumen. Quality of 4D flow visualization and CE-MRA images depended on stent type and stent orientation relative to the magnetic field. Compared to the visible lumen area determined by 3D CE-MRA, estimates of lumen patency derived from 4D flow measurements were significantly higher and less dependent on stent type. A higher number of stents could be assessed for in-stent patency by 4D phase contrast flow imaging (n=14) than by 2D phase contrast flow imaging (n=10).

CONCLUSIONS

4D phase contrast flow imaging in peripheral vascular stents is feasible and appears advantageous over conventional 3D contrast-enhanced MR angiography and 2D phase contrast flow imaging. It allows for in-stent flow visualization and flow quantification with varying quality depending on stent type.

Internal cranial expansion surgery for the treatment of refractory idiopathic intracranial hypertension

OBJECT

Idiopathic intracranial hypertension (IIH) may be refractory to available medical and surgical therapies. Patients with this condition may suffer from intractable headaches, experience visual deterioration, or have other symptoms related to elevated intracranial pressure. Internal cranial expansion (ICE) is a novel surgical procedure that the authors have developed for the treatment of patients with this condition. Here, they describe ICE and present their initial experience in using this surgical procedure for the treatment of patients with refractory IIH.

METHODS

The authors conducted a retrospective review of 10 consecutive patients who underwent ICE for the treatment of IIH during a 5-year period. Preoperative and postoperative clinical parameters including patient symptoms, presence of papilledema, and available ICP or CSF opening pressures were compared. Procedural details and complications were noted. Intracranial volume increases were calculated using available pre- and postoperative CT scans.

RESULTS

Follow-up for the 10 patients in this series ranged from 1 to 39.6 months (mean 15.5 months). Technically successful ICE was performed in all patients within the cohort. Surgical complications included a single postoperative seizure in one patient and a sagittal sinus tear with no clinical sequelae in another patient. At the time of last follow-up, 7 (70%) of 10 patients were either symptomatically improved or asymptomatic. Six (67%) of 9 patients with preoperative headaches had reduction or resolution of this symptom, and all patients (4 of 4) with preoperative papilledema had a reduction in or complete resolution of this sign. Postoperative ICP or CSF opening pressures were normal in all patients (4 of 4) tested. Postoperative intracranial volume expansion ranged between 3.8% and 12%.

CONCLUSIONS

Internal cranial expansion is a safe and effective surgery for the treatment of patients with refractory IIH. This surgery expands the intracranial volume and thus promotes ICP normalization, which may lead to the reduction or complete resolution of the signs and symptoms of IIH. Internal cranial expansion may be used as part of a multidisciplinary management approach in the treatment of refractory IIH.

Current diagnosis and management of symptomatic intracranial atherosclerotic disease

PURPOSE OF REVIEW

Intracranial atherosclerotic disease (IAD) is likely the most common cause of stroke world-wide and is associated with a very high risk of recurrence. It results in cerebral ischemia due to a variety of mechanisms, including artery-to-artery embolism, hemodynamic failure, and occlusion of penetrating arteries. New imaging modalities focused on physiological consequences of IAD have become available and recent treatment trials have been completed.

RECENT FINDINGS

We review the traditional imaging modalities, emphasizing the advantages and limitations of each method, and discuss the novel physiological approaches that interrogate physiological process to indicate specific mechanisms of ischemia. These allow deeper understanding of the pathophysiological processes that underlie IAD-related ischemia. The key findings of recent therapeutic trials are reviewed, including the landmark randomized studies showing advantage of antiplatelet agents and risk factor modification, and a significant risk of complications with endovascular approaches.

SUMMARY

Current evidence argues for aggressive medical management and suggests caution with interventional treatments. We propose that mechanistic information will further refine the risk assessment of patients with IAD to offer targeted therapy.

MR angiography and imaging for the evaluation of middle cerebral artery atherosclerotic disease

Intracranial atherosclerotic disease may constitute the most common cause of ischemic stroke worldwide; yet, in the developed world, imaging research has largely focused on extracranial atherosclerosis. Many studies in populations of Asian, African, and Hispanic descent demonstrate the preponderance of intracranial stenosis compared with carotid stenosis. This review examines the clinical presentations of MCA atherosclerosis and stenosis and the use of noninvasive MR imaging in the assessment of intracranial vasculature. MRA is a well-validated technique that offers great advantage over traditional angiography. Advances in high-resolution MR imaging of MCA stenosis have the potential to yield excellent visualization of plaque. Future developments in high-resolution MR imaging to depict intracranial atherosclerosis are explored in this review; these advances will guide endovascular therapy and the comparison of novel interventions.

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

BACKGROUND AND PURPOSE

Large-vessel cerebral blood flow quantification has emerged as a potential predictor of stroke risk. QMRA uses phase-contrast techniques to noninvasively measure vessel flows. To evaluate the in vivo accuracy of QMRA for measuring the effects of progressive arterial stenosis, we compared this technique with invasive flow measurements from a sonographic transit-time flow probe in a canine model.

MATERIALS AND METHODS

A sonographic flow probe was implanted around the CCA of hound dogs (n = 4) under general anesthesia. Pulsatile blood flow and arterial pressure were continuously recorded during CCA flow measurements with QMRA. A vascular tourniquet was applied around the CCA to produce progressive stenosis and varying flow rates. Statistical comparisons were made by using the Pearson product moment correlation coefficient.

RESULTS

A total of 60 paired CCA flow measurements were compared. Mean blood flows ranged between 21 and 691 mL/min during QMRA acquisition as measured by the flow probe. The correlation coefficients between flow probe and QMRA measurements for mean, maximum, and minimum volume flow rates were 0.99 (P < .0001), 0.98 (P < .0001), and 0.96 (P < .0001), respectively. The overall proportional difference between the 2 techniques was 7.8 ± 1%. Measurements at higher flow rates and in the absence of arterial stenosis had the lowest PD.

CONCLUSIONS

Noninvasive CCA flow measurements by using QMRA are accurate compared with invasive flow-probe measurements in a canine arterial flow model with stenosis and may be useful for the evaluation of the hemodynamic effects of stenosis caused by cerebrovascular atherosclerosis.

Clinical utility of quantitative magnetic resonance angiography in the assessment of the underlying pathophysiology in a variety of cerebrovascular disorders

BACKGROUND

Quantitative MRA (qMRA) is a relatively new technique that uses traditional time-of-flight and phase-contrast MRI to visualize extracranial and intracranial vascular anatomy and measure volumetric blood flow. We aimed to assess the clinical utility of qMRA in assessing the hypothesized pathophysiology (HP) in a range of cerebrovascular diseases. Moreover, we postulated that evaluation of the arterial waveforms, can improve the evaluation of the hypothesized pathophysiology by qMRA.

METHODS

We reviewed studies from 10 patients who underwent qMRA examinations before and after their treatments. Two reviewers assessed the anatomy, volumetric flow rates and arterial waveforms for each vessel sampled and reached a consensus as to whether the above parameters supported the clinical diagnosis/hypothesized pathophysiology and the subsequent management.

FINDINGS

All 20 qMRA studies were technically adequate. qMRA supported the HP in all 10 patients as determined by abnormal volumetric flow values in the affected vessels before treatment and by the correction of these abnormal values in the patients whose treatment was successful. Each of our five patients with occlusive disease/vasoconstriction demonstrated evidence of dampening of the arterial waveforms distally to the narrowed artery (parvus-tardus phenomenon). The parvus-tardus effect disappeared after treatment.

CONCLUSION

qMRA is unique in combining time-of-flight MRA in a complementary manner with phase-contrast MRA to obtain volumetric flow values and potentially important physiologic information from arterial waveform analysis in patients with a range of cerebrovascular diseases during the course of a single MR examination.

Detection of intracranial in-stent restenosis using quantitative magnetic resonance angiography

BACKGROUND AND PURPOSE

In-stent restenosis (ISR) after angioplasty/stenting for intracranial stenosis has been reported in up to 25% to 30% of patients. Detection and monitoring of ISR relies primarily on serial catheter angiography, because noninvasive imaging methods are typically hampered by stent-related artifact. We examined the value of serial vessel flow measurements using quantitative magnetic resonance angiography (QMRA) in detection of ISR.

MATERIAL AND METHODS

Records of patients undergoing stenting for intracranial symptomatic stenosis >50% between 2005 and 2009 were retrospectively reviewed. Angiographic images were graded by a blinded neurointerventionalist for stenosis pretreatment, immediately after treatment, and during follow-up. Flow in the affected vessel measured by QMRA was recorded; > 25% reduction in flow was considered indicative of an adverse change. Clinical data regarding neurological outcome were also collected.

RESULTS

Twenty-eight patients underwent stenting during the time interval studied. Of these, 12 patients (mean age, 55.5 years; 8 female) had contemporaneous angiography and QMRA and were analyzed. Median follow-up was 9 months. Six patients (50%) demonstrated angiographic restenosis 2 to 12 months after treatment; all had an analogous decrease in flow in the vessel of interest. Of 3 patients with more severe flow decrement (> 50%), 2 experienced stroke. None of the patients without angiographic ISR demonstrated a flow decrease on QMRA.

CONCLUSIONS

In this preliminary series, flow decrease on QMRA is highly predictive of angiographic ISR. Additionally, the degree of flow decrement correlates with symptomatic ISR. QMRA may provide a useful noninvasive tool for serial monitoring after intracranial stenting.

Angiographic CT after intravenous contrast agent application: A noninvasive follow-up tool after intracranial angioplasty and stenting

BACKGROUND AND PURPOSE

ICAS is one of the therapeutic options in symptomatic cerebral artery stenosis. iaDSA is the current criterion standard examination after ICAS for the detection of ISR. In this study, we evaluated ivACT as a potential noninvasive follow-up alternative.

MATERIALS AND METHODS

In 17 cases, ivACT and iaDSA were performed after ICAS. Both procedures were carried out on a flat-panel-detector-equipped angiography system. Postprocessing of ivACT acquisitions was performed on a dedicated workstation producing multiplanar reformations of the stent region and other intracranial arteries. Restenotic lesions were compared with iaDSA measurements. All studies were independently evaluated by 2 experienced neuroradiologists blinded to patients data.

RESULTS

In 5 cases, ISR was diagnosed on iaDSA images. All restenotic lesions were reliably detected (sensitivity, 100%; 95%CI, 48%-100%) and could be correctly quantified on ivACT images in comparison with iaDSA. The neuroradiologists correctly excluded ISR in 11 of 12 lesions after viewing the ivACT examinations (specificity, 92%; 95%CI, 62%-100%). Measurements of ISR on ivACT were highly correlated to iaDSA (Pearson r = 0.94, P < .01).

CONCLUSIONS

IvACT is a promising noninvasive follow-up examination after ICAS. With its high spatial resolution, it can reliably detect or exclude ISR. Contrary to iaDSA, there is no need for a recovery period after ivACT and the risk of neurologic complications is practically lowered to zero.