Arterial Spin Labeling Magnetic Resonance Imaging Estimation of Antegrade and Collateral Flow in Unilateral Middle Cerebral Artery Stenosis

Distinguishing stroke from transient ischemic attack using plaque characteristics and arterial transit artifacts

Purpose

We aimed to investigate the differences in plaque characteristics and hemodynamics in patients with ischemic stroke and transient ischemic attack (TIA), comparing the diagnostic abilities of high-resolution magnetic resonance imaging (HRMRI) and arterial spin labeling (ASL) for ischemic stroke.

Methods

This retrospective analysis included patients who underwent HRMRI and ASL between October 2020 and December 2023. We compared clinical risk factors, vascular plaque characteristics, and the presence of arterial transit artifacts (ATAs) at post-labeling delays (PLDs) of 1.5-s and 2.5-s between stroke and TIA groups. Multivariate logistic regression analysis was used to evaluate the diagnostic performance of different prediction models combining clinical factors, differential plaque characteristics, and the presence of ^PLD ATAs.

Results

A total of 147 patients (mean age, 57.12 ± 13.08 years; 102 men) were initially included in this study, divided into stroke (79) and TIA (68) groups. Significant differences in vascular positive remodeling, intraplaque hemorrhage, enhancement ratio, and the presence of 1.5-s and 2.5-s ATAs (p < 0.05) were observed between groups. Combined HRMRI and ASL performed best in distinguishing ischemic stroke and TIA (area under the curve [AUC], 0.926; 95% confidence interval [CI], 0.885-0.967), with no significant difference in ischemic stroke diagnostic performance between HRMRI and ASL (95% CI, -0.039 to 0.087, Z = 0.742, p = 0.458).

Conclusion

A model combined with plaque characteristics and ATAs showed good diagnostic performance in distinguishing between TIA and stroke in patients with intracranial atherosclerotic stenosis. ASL provides a simpler imaging evaluation method than HRMRI, and ATA evaluation may become a more widely used imaging marker in clinical practice.

Enhanced Benefit of STA-MCA Bypass Surgery in Chronic Terminal Internal Carotid and/or Middle Cerebral Artery Occlusion Patients With Impaired Collateral Circulation: Introducing a Novel Assessment Approach for Collateral Compensation

Background: Ischemic stroke is one of the major emergency diseases leading to death and disability worldwide, characterized by its acute onset and the urgent need for prompt medical intervention to reduce mortality and long-term disability. Chronic terminal internal carotid artery and/or middle cerebral artery occlusion (CTI/MCAO) is an important subtype of intracranial artery occlusive disease. The superficial temporal artery-to-MCA (STA-MCA) bypass has been proposed to improve cerebral blood flow (CBF) and cerebrovascular reserve (CVR), potentially enhancing neurological outcomes. However, its safety and efficacy in CTI/MCAO patients remain controversial. Methods: A total of 107 CTI/MCAO patients from Nanjing Brain Hospital, enrolled between July 2019 and June 2022, were divided into surgical and medical treatment groups. Cerebral perfusion and collateral formation were evaluated using pseudocontinuous arterial spin labeling (pCASL) and digital subtraction angiography (DSA). Modified Rankin scale (mRS) score and complication rates were compared between the two groups. In addition, correlations between Matsushima grades, early-arriving flow proportion (EFP), and lesion-side cerebrovascular (LCBV) scores were analyzed. Results: The surgical group showed significantly lower mRS scores than the medical group (p=0.018), with no significant differences in complication rates at the 6-month follow-up (p=0.861). CBF differed significantly among affected MCA segments (p < 0.001), particularly in the insular and opercular regions (M2-M3) (p=0.006). Matsushima grades in unilateral CTI/MCAO patients were negatively correlated with preoperative LCBV scores (γ s = -0.468, p=0.005) and EFP (γ s = -0.648, p=0.007). EFP demonstrated high accuracy in predicting LCBV scores in CTI/MCAO patients (AUC = 0.902, p=0.004). Conclusion: STA-MCA bypass surgery improved neurological outcomes in CTI/MCAO patients, particularly those with poor preoperative collateral compensation. EFP may serve as a reliable, noninvasive tool for assessing collateral circulation status in this population.

Morphological Study on Lenticulostriate Arteries in Patients With Middle Cerebral Artery Stenosis at 7 T MRI

BACKGROUND

Middle cerebral artery (MCA) stenosis affects lenticulostriate arteries (LSAs) that supply the basal ganglia. Increased spatial resolution and signal-to-noise ratio of 7 T could facilitate morphological imaging of very-small-diameter LSAs.

PURPOSE

To evaluate differences in morphological characteristics of LSA among different MCA stenoses.

STUDY TYPE

Prospective.

SUBJECTS

We enrolled 161 patients (age: 26-83 years, 115 males) with MCA-M1-segment stenosis, and assigned them to the symptomatic (ischemic stroke on imaging, or transient ischemic attack diagnosed clinically within 90 days) and asymptomatic (mild-to-moderate stenosis, ≤70% diameter reduction and severe stenosis, >70% and ≤99% diameter reductions) groups and further subdivided them into the proximal and distal stenosis subgroups.

FIELD STRENGTH/SEQUENCE

7 T, three-dimensional time-of-flight magnetic resonance angiography (3D TOF-MRA).

ASSESSMENT

The number of LSA stems, branches, length, and tortuosity (LSA length/linear distance between LSA start- and endpoints) were evaluated independently in both hemispheres by 3 radiologists with 2-, 10-, and 12-years' experience, and inter-group and inter-subgroup comparisons were undertaken.

STATISTICAL TESTS

Independent t tests, paired t tests, chi-square test, and multiple linear regression analysis (P < 0.05 indicated statistical significance).

RESULTS

Compared with the asymptomatic group (N = 76), the symptomatic group (N = 85) had significantly fewer LSA branches (7.58 ± 2.31 vs. 9.29 ± 2.37) and shorter length (4.32 ± 0.84 vs. 4.59 ± 0.72 cm). There were no significant intergroup differences in LSA morphological characteristics between the mild-to-moderate and severe-stenosis subgroups (LSA stems: P = 0.457, LSA branches: P = 0.433, LSA length: P = 0.150, and LSA tortuosity: P = 0.613). The proximal stenosis subgroup had significantly fewer (8.08 ± 1.80 vs. 10.64 ± 2.21) and shorter LSA branches (4.43 ± 0.69 vs. 4.76 ± 0.71 cm) than in the distal stenosis subgroup. Multiple linear regression, after false discovery rate correction, showed that symptoms and the MCA-M1-segment-stenosis site (proximal/distal) were significantly associated with LSA and length.

DATA CONCLUSION

Having symptoms and a proximal MCA-M1 segment stenosis were associated with fewer LSA branches, whereas stenosis severity did not significantly affect LSA morphological characteristics.

PLAIN LANGUAGE SUMMARY

Lenticulostriate arteries mainly originate from the middle cerebral artery, which 7 T magnetic resonance imaging (MRI) can help visualize effectively. We mainly focused on evaluating lenticulostriate artery stems, branches, length, and tortuosity (length/linear distance between start- and endpoints) among 3 types of middle cerebral artery stenoses (symptomatic and asymptomatic, mild-to-moderate and severe stenosis, and proximal and distal stenosis). Symptomatic patients with proximal MCA stenosis had fewer lenticulostriate artery branches (7.58 ± 2.31 vs. 9.29 ± 2.37 and 8.08 ± 1.80 vs. 10.64 ± 2.21). This research based on the morphological perspective clearly depicted the lenticulostriate artery using 7 T MRI to provide more intuitive results.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 3.

Spatial coefficient of variation of arterial spin labeling magnetic resonance imaging can predict decreased cerebrovascular reactivity measured by acetazolamide challenge single-photon emission tomography

PURPOSE

The aim of this study was to investigate whether the spatial coefficient of variation of arterial spin labeling (ASL-CoV) acquired in clinical settings can be used to estimate decreased cerebrovascular reactivity (CVR) measured with single-photon emission computed tomography (SPECT) and acetazolamide challenge in patients with atherosclerotic stenosis of intra- or extracranial arteries.

METHODS

We evaluated the data of 27 atherosclerotic stenosis patients who underwent pseudocontinuous ASL and SPECT. After spatial normalization, regional values were measured using the distributed middle cerebral artery territorial atlas of each patient. We performed comparisons, correlations, and receiver operating characteristic (ROC) curve analyses between ASL-cerebral blood blow (CBF), ASL-CoV, SPECT-CBF and SPECT-CVR.

RESULTS

Although the ASL-CBF values were positively correlated with SPECT-CBF values (r = 0.48, 95% confidence interval (CI) = 0.28-0.64), no significant difference in ASL-CBF values was detected between regions with and without decreased CVR. However, regions with decreased CVR had significantly greater ASL-CoV values than regions without decreased CVR. SPECT-CVR was negatively correlated with ASL-CoV (ρ = -0.29, 95% CI = -0.49 - -0.06). The area under the ROC curve of ASL-CoV in predicting decreased CVR (0.66, 95% CI = 0.51-0.81) was greater than that of ASL-CBF (0.51, 95% CI = 0.34-0.68). An ASL-CoV threshold value of 42% achieved a high specificity of 0.93 (sensitivity = 0.42, positive predictive value = 0.77, and negative predictive value = 0.75).

CONCLUSION

ASL-CoV acquired by single postlabeling delay without an acetazolamide challenge may aid in the identification of patients with decreased CVR on SPECT.

Three-dimensional pseudocontinuous arterial spin labeling with dual postlabeling delay for reflecting cerebral blood flow regulation in patients with hydrocephalus: a retrospective cross-sectional study

Background

Three-dimensional pseudo-continuous arterial spin-labeling (3D pCASL) with dual postlabeling delay (PLD) captures both early and delayed cerebral blood flow (CBF), yet its potential in reflecting blood flow regulation in hydrocephalus patients remains uncertain. This study investigated the hemodynamic characteristics in patients with hydrocephalus and whether the difference in cerebral blood flow using short and long PLDs (ΔCBF = CBFPLD =2.5 s - CBFPLD =1.5 s) could reflect cerebral regulation and further aimed to demonstrate the associations between regional ΔCBF and the degree of ventricular dilatation.

Methods

This retrospective study included consecutive patients with hydrocephalus and control participants attending The Second Affiliated Hospital of Nanchang University from December 2017 to December 2022. The CBF in 18 brain regions was manually delineated by two radiologists. Regional CBF and ΔCBF were compared via covariance analyses. The associations between ΔCBF and the degree of ventricular dilatation were investigated using linear regression analyses and interaction analysis.

Results

In total, 58 patients with communicating hydrocephalus, 57 patients with obstructive hydrocephalus, and 52 controls were analyzed. CBF of the hydrocephalus groups was lower than that of the control group at the shorter PLD. CBF was higher at a longer PLD, with no difference between the hydrocephalus groups and the control group in some regions. The hydrocephalus groups showed a higher ΔCBF compared to the control group. Furthermore, in the left medial watershed (10.6±5.66 vs. 7.01±5.88 mL/100 g/min; P=0.038), communicating hydrocephalus exhibited greater ΔCBF than did obstructive hydrocephalus. ΔCBF of the right posterior external watershed [adjusted β: 0.276; 95% confidence interval (CI): 0.047-0.505; P=0.019] and right parietal cortex (adjusted β: 0.277; 95% CI: 0.056-0.498; P=0.015) in the obstructive hydrocephalus group and ΔCBF of the left internal watershed (adjusted β: 0.274; 95% CI: 0.013-0.536; P=0.040) in the communicating hydrocephalus group were associated with the degree of ventricular dilatation, respectively.

Conclusions

Patients with hydrocephalus showed cerebral regulation in maintaining adequate CBF, resulting in longer arterial transit times. The ability to regulate CBF in brain regions represented by the watershed was associated with the degree of ventricular dilation.

Imaging Assessments and Clinical Significance of Brain Frailty in Moyamoya Disease

BACKGROUND AND PURPOSE

Imaging assessment of brain frailty in ischemic stroke has been extensively studied, while the correlation between brain frailty and Moyamoya disease remains obscure. This study aimed to investigate the imaging characteristics of brain frailty and its clinical applications in Moyamoya disease.

MATERIALS AND METHODS

This study included 60 patients with Moyamoya disease (107 hemispheres). All patients were divided into stroke and nonstroke groups based on clinical symptoms and imaging findings. The modified brain frailty score was adapted to consider 4 imaging signs: white matter hyperintensity, enlargement of perivascular space, old vascular lesions, and cerebral microbleed. The relative CBF of the MCA territory was quantified using pseudocontinuous arterial-spin labeling. Surgical outcome after revascularization surgery was defined by the Matsushima grade.

RESULTS

The relative CBF of the MCA territory decreased as the modified brain frailty score and periventricular white matter hyperintensity grades increased (ρ = -0.22, P = .02; ρ = -0.27, P = .005). Clinically, the modified brain frailty score could identify patients with Moyamoya disease with stroke (OR = 2.00, P = .02). Although the modified brain frailty score showed no predictive value for surgical outcome, basal ganglia enlargement of the perivascular space had a significant correlation with the postoperative Matsushima grade (OR = 1.29, P = .03).

CONCLUSIONS

The modified brain frailty score could reflect a cerebral perfusion deficit and clinical symptoms of Moyamoya disease, and its component basal ganglia enlargement of perivascular space may be a promising marker to predict surgical outcome and thus aid future clinical decision-making.

Differences between Acute Embolic and Atherosclerotic Middle Cerebral Artery Occlusion in Multiphase Arterial Spin-labeling Imaging

Arterial spin-labeling magnetic resonance imaging (ASL-MRI) is widely used for evaluating collateral development in patients with acute ischemic stroke (AIS). This study aimed to characterize the findings of multiphase ASL-MRI between embolic and atherosclerotic large vessel occlusion (LVO) to aid in the differential diagnosis. Among 982 patients with AIS, 44 who were diagnosed with acute, symptomatic, and unilateral occlusion of the horizontal segment of the middle cerebral artery (MCA) were selected and categorized into embolic stroke (ES) and atherosclerosis (AT) groups. Using ASL-MRI (postlabeling delay [PLD] of 1.5, 2.0, and 2.5 s) at admission, the ipsilateral to contralateral ratio (ICR) of the signal intensity and its time-course increasing rate (from PLD 1.5 to 2.0 and 2.5, ΔICR) were measured and compared between the two groups. The mean ICR was significantly higher in the AT group than in the ES group (AT vs. ES: 0.49 vs. 0.27 for ICR1.5, 0.73 vs. 0.32 for ICR2.0, and 0.92 vs. 0.37 for ICR2.5). The ΔICR of PLD 1.5-2.0 (ΔICR2.0) and 2.5 (ΔICR2.5) were also significantly higher in the AT group than in the ES group (AT vs. ES: 50.9% vs. 26.3% for ΔICR2.0, and 92.6% vs. 42.9% for ΔICR2.5). Receiver operating characteristic curves showed moderate-to-strong discriminative abilities of each ASL-MRI parameter in predicting MCA occlusion etiology. In conclusion, multiphase ASL-MRI parameters may aid in differentiating intracranial LVO etiology during the acute phase. Thus, it is applicable to AIS management.

Clinical and imaging predictors for hemorrhagic transformation of acute ischemic stroke after endovascular thrombectomy

BACKGROUND AND PURPOSE

Hemorrhagic transformation (HT) is a common complication of endovascular thrombectomy (EVT) in patients with acute ischemic stroke (AIS). Our study aims to investigate the clinical and imaging predictors of HT and symptomatic intracranial hemorrhage (sICH) in patients who underwent EVT.

METHODS

A retrospective analysis of 118 patients undergoing EVT for acute anterior circulation stroke was performed. Potential clinical and imaging predictors of all patients were collected and multivariate logistic regression was performed. The risk prediction system was constructed according to the multivariate logistic regression results.

RESULTS

The incidence of HT and sICH after EVT were 46.6% and 15.3%, respectively. The multivariate logistic regression results showed that Alberta Stroke Program Early CT Score (ASPECTS) (p = .001, odds ratio [OR] = 0.367, 95% [confidence interval] CI, 0.201-0.670), collateral status (p<.001, OR = 0.117, 95% CI, 0.042-0.325), relative cerebral blood flow (CBF) ratio (p = .025, OR = 0.943, 95% CI, 0.895-0.993), and blood glucose on admission (p = .012, OR = 1.258, 95% CI, 1.053-1.504) were associated with HT. While for sICH, collateral circulation (p = .007, OR = 0.148, 95% CI, 0.037-0.589), ASPECTS (p = .033, OR = 0.510, 95% CI, 0.274-0.946), and blood glucose (p = .005, OR = 1.304, 95% CI, 1.082-1.573) were independent factors. The predictive model for HT after EVT was established, and the sensitivity and specificity of it were 90.9% and 79.4%, respectively, with the area under the curve of 90.0% (84.5%-95.4%).

CONCLUSION

Collateral status, ASPECTS, relative CBF ratio, and blood glucose on admission were predictors for HT in AIS patients, while collateral status, ASPECTS, and blood glucose on admission were also predictors for sICH. In addition, the established predictive model showed good diagnostic value for prediction of HT after EVT.

Arterial transit artifact as a short-term prognostic indicator in acute ischemic stroke

BACKGROUND

Arterial transit artifact (ATA) observed on arterial spin labeling (ASL) was recently suggested to be associated with improved functional outcomes following acute ischemic stroke (AIS). AIS is a heterogeneous disease with diverse pathogenic mechanisms depending on the stroke subtype. This study aimed to investigate the association between ATA and 3-month functional outcomes in AIS patients according to etiology subtypes.

METHODS

Consecutive patients with AIS were included. All patients underwent ASL MRI with postlabeling delay (PLD) of 1.5 and 2.5 s. ATA was assessed from the ASL images of both PLDs. Stroke etiologic subtypes were determined according to the modified TOAST (Trial of ORG 10172 in Acute Stroke Treatment) classification. Short-term functional outcomes were evaluated using the 3-month modified Rankin scale (mRS). Log-binomial regression was applied to analyze the association between ATA and functional outcomes at 3 months after stroke.

RESULTS

Ninety-eight AIS patients (62.73 ± 13.05 years; 68 men) were finally included. ATA was detected in forty-six patients and most frequently seen in the large-artery atherosclerosis (LAA) subtype (35/46). The ATA group exhibited a lower percentage of patients with mRS > 2 compared to the group without ATA (36.5% vs. 19.6%; P < 0.001). ATA was independently associated with better 3-month clinical outcomes (adjusted risk ratio, 0.35[95% CI, 0.16-0.74]) in the multivariate log-binomial regression model. After stratification by TOAST subtypes, a significant association was found between ATA and better outcomes in the LAA subtype (adjusted risk ratio, 0.20[ 95% CI, 0.05-0.72]) but not in cardioembolism and small artery occlusion (SVO) subtype.

CONCLUSION

ATA is associated with better outcomes at 3 months in patients with AIS, especially in the LAA subtype, but this association attenuated in the cardioembolism and SVO subtypes.

A comparative study of multi and single post labeling delay pseudocontinuous arterial spin labeling in patients with carotid artery stenosis

PURPOSE

Arterial Spin Labeling (ASL) allows for the non-invasive visualization of brain perfusion to detect abnormalities. In unilateral carotid artery stenosis, one hemisphere is less supplied with blood which results in a lower cerebral blood flow (CBF) compared to the healthy side. ASL can be performed time-resolved using multiple post labeling delay (PLD) times after labeling or static with a single delay, the latter allowing for a faster and more robust acquisition while bearing the risk of a falsely set delay resulting in unusable images. The purpose of this study is to compare the performance of multi-PLD and single-PLD ASL in patients with unilateral carotid artery stenosis both as means of diagnosis and therapeutic follow-up examination.

METHODS

ASL perfusion data of 17 patients with known unilateral carotid artery stenosis was used to compare the diagnostic performance of the multi-PLD and single-PLD approach. Comparisons were made based on the CBF values and the added benefit of arrival time maps showing slower blood flow in multi-PLD ASL which might be overlooked in the individual delay images both before and after therapy.

RESULTS

Both the multi-PLD and the single-PLD data could identify the side of the stenosis with hemispheric differences in each approach (p < 0.001) and depict the normalization of CBF after therapy (p > 0.05). There were no differences between the individual methods (p > 0.05).

CONCLUSION

In this work, we could show that multi-PLD ASL in patients with unilateral carotid artery stenosis is beneficial as it provides both CBF and arrival time maps, however when only a single-PLD acquisition is available, this appears sufficient in a clinical setting to investigate the presence of a unilateral stenosis.

Evaluation of the Ischemic Penumbra and Prognosis in acute Cerebral Infarction Using Cerebral Blood Flow and Delay Time Derived from Multi-delay pCASL Imaging

PURPOSE

The purpose of this study was to evaluate the ischemic penumbra and prognosis in acute cerebral infarction using cerebral blood flow (CBF) and delay time (DT) derived from multi-delay pseudo-continuous arterial spin-labeling (pCASL) imaging and to estimate the possible use of such indices to predict prognosis.

METHOD

Our subjects comprised 25 patients who were diagnosed with cerebral infarction in our stroke center between September 2017 and December 2018 and underwent pCASL perfusion MRI. The time from onset to MRI was 0.6 to 20 h (mean, 6 h) and was less than 4.5 h in 16 patients. Twelve patients received conservative treatment, three were treated with tPA, and the remaining 10 patients underwent invasive treatment (e.g., thrombectomy). They were subdivided by recanalization:18 patients were non-recanalized and 7 were recanalized. We evaluated the mean cerebral blood flow (CBF) and mean arterial transit DT at the infarct core and penumbra and the infarct size at the initial and follow-up examinations and calculated the infarct enlargement ratio (ER) from the initial and final infarct sizes. We also assessed clinical prognosis by using the initial and final NIHSS scores. We investigated the relationship among the ASL, ER, and NIHSS parameters and determined predictors of infarct enlargement using logistic analysis.

RESULT

The degree of the CBF decrease was related to the size of the initial infarct lesion (CBF at core:r=-0.4060, p=0.044;CBF at penumbra:r=-0.4970, p=0.012) and initial NIHSS (r=-0.451, p=0.024;CBF at penumbra:r=-0.491, p=0.013). Because no parameters were correlated with the ER in all patients. Specifically in the non-recanalization group, the DT at the penumbra was positively correlated with the ER (r=-0.496, p=0.034). Moreover, by logistic regression analysis, the DT at the penumbra was the only independent predictor of infarct enlargement in all patients (p=0.047) and in non-recanalization patients (p=0.036).

CONCLUSION

The only parameter predicting the ER was the mean DT at the penumbra, and the tendency was affected by recanalization status. DT obtained by multi-delay ASL may become a prognostic index of acute cerebral infarction. J. Med. Invest. 71 : 286-292, August, 2024.

MRI Assessment of Brain Frailty and Clinical Outcome in Patients With Acute Posterior Perforating Artery Infarction

BACKGROUND

Global brain health has gained increasing attention recently. Imaging markers of brain frailty have been related to functional outcomes in previous studies on anterior circulation; however, little data are available on imaging markers and posterior circulation.

PURPOSE

To investigate the impact of brain frailty on functional outcomes in patients with acute perforating artery infarction (PAI) of the posterior circulation.

STUDY TYPE

Prospective.

POPULATION

One hundred patients (60.78 ± 9.51 years, 72% men) with acute posterior circulation PAI (determined by diffusion-weighted magnetic resonance imaging (MRI)/time-of-flight MR angiography).

FIELD STRENGTH/SEQUENCE

T1- and T2-weighted fast spin echo, T2-weighted fluid-attenuated inversion recovery, diffusion-weighted echo planar, gradient echo (susceptibility-weight imaging), and 3D time-of-flight MR angiography sequences at 3.0 T.

ASSESSMENT

Periventricular and deep white matter hyperintensities (WMH), enlarged perivascular spaces (EPVS) in the basal ganglia and centrum semiovale area, lacunes, cerebral microbleeds (CMB), and total brain frailty score by calculating the above imaging characters were rated visually by three radiologists with 9, 10, and 11 years of experience and one neuroradiologist with 12. Infarction volume was assessed using baseline diffusion-weighted imaging (DWI) data obtained within 24 hours of symptom onset. A modified Rankin Scale (mRS) score >1 on day 90 defined an adverse functional outcome. Associations between the imaging markers of brain frailty and functional outcomes were assessed.

STATISTICAL TESTS

Fisher's exact test, Mann-Whitney U test, and multivariable binary logistic regression. A P value <0.05 was considered statistically significant.

RESULTS

Adverse prognoses (mRS > 1) were observed in 34 (34%) patients. Infarction volume, periventricular WMH, deep WMH, basal ganglia EPVS, CMB, and the brain frailty score were significantly associated with adverse functional outcomes. An increased brain frailty score was significantly associated with unfavorable mRS score on day 90 (odds ratio 1.773, 95% confidence interval 1.237-2.541).

DATA CONCLUSION

Advanced MRI imaging markers of brain frailty, individually or combined as a total brain frailty score, were associated with worse functional outcomes after acute posterior circulation PAI.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY: Stage 3.

Cerebral haemodynamics in symptomatic intracranial atherosclerotic disease: a narrative review of the assessment methods and clinical implications

Intracranial atherosclerotic disease (ICAD) is a common cause of ischaemic stroke and transient ischaemic attack (TIA) with a high recurrence rate. It is often referred to as intracranial atherosclerotic stenosis (ICAS), when the plaque has caused significant narrowing of the vessel lumen. The lesion is usually considered 'symptomatic ICAD/ICAS' (sICAD/sICAS) when it has caused an ischaemic stroke or TIA. The severity of luminal stenosis has long been established as a prognostic factor for stroke relapse in sICAS. Yet, accumulating studies have also reported the important roles of plaque vulnerability, cerebral haemodynamics, collateral circulation, cerebral autoregulation and other factors in altering the stroke risks across patients with sICAS. In this review article, we focus on cerebral haemodynamics in sICAS. We reviewed imaging modalities/methods in assessing cerebral haemodynamics, the haemodynamic metrics provided by these methods and application of these methods in research and clinical practice. More importantly, we reviewed the significance of these haemodynamic features in governing the risk of stroke recurrence in sICAS. We also discussed other clinical implications of these haemodynamic features in sICAS, such as the associations with collateral recruitment and evolution of the lesion under medical treatment, and indications for more individualised blood pressure management for secondary stroke prevention. We then put forward some knowledge gaps and future directions on these topics.

Multidelay MR Arterial Spin Labeling Perfusion Map for the Prediction of Cerebral Hyperperfusion After Carotid Endarterectomy

BACKGROUND

Multidelay arterial spin labeling (ASL) generates time-resolved perfusion maps, which may provide sufficient and accurate hemodynamic information in carotid stenosis.

PURPOSE

To use imaging markers derived from multidelay ASL magnetic resonance imaging (MRI) and to determine the optimal strategy for predicting cerebral hyperperfusion after carotid endarterectomy (CEA).

STUDY TYPE

Prospective observational cohort.

SUBJECTS

A total of 79 patients who underwent CEA for carotid stenosis.

FIELD STRENGTH/SEQUENCE

A 3.0 T/pseudo-continuous ASL with three postlabeling delays of 1.0, 1.57, and 2.46 seconds using fast-spin echo readout.

ASSESSMENT

Cerebral perfusion pressure, antegrade, and collateral flow were scored on a four-grade ordinal scale based on preoperative multidelay ASL perfusion maps. Simultaneously, quantitative hemodynamic parameters including cerebral blood flow (CBF), arterial transit time (ATT), relative CBF (rCBF) and relative ATT (rATT; ipsilateral/contralateral values) were calculated. On the CBF ratio map obtained through dividing postoperative by preoperative CBF map, regions of interest were placed covering ipsilateral middle cerebral artery territory. Three neuroradiologists conducted this procedure. Cerebral hyperperfusion was defined as a CBF ratio >2.

STATISTICAL TESTS

Weighted κ values, independent sample t test, chi-square test, Mann-Whitney U-test, multivariable logistic regression analysis, receiver-operating characteristic curve analysis, and Delong test. Significance level was P < 0.05.

RESULTS

Cerebral hyperperfusion was observed in 15 (19%) patients. Higher blood pressure (odd ratio [OR] = 1.08) and carotid near-occlusion (NO; OR = 7.31) were clinical risk factors for postoperative hyperperfusion. Poor ASL perfusion score (OR = 37.33), decreased CBF (OR = 0.74), prolonged ATT (OR = 1.02), lower rCBF (OR = 0.91), and higher rATT (OR = 1.12) were independent imaging predictors of hyperperfusion. ASL perfusion score exhibited the highest specificity (95.3%), while CBF exhibited the highest sensitivity (93.3%) for the prediction of hyperperfusion. When combined with ASL perfusion score, CBF and ATT, the predictive ability was significantly higher than using blood pressure and NO alone (AUC: 0.98 vs. 0.78).

DATA CONCLUSIONS

Multidelay ASL can accurately predict cerebral hyperperfusion after CEA with high sensitivity and specificity.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 5.

Effect of arteriosclerotic intracranial arterial vessel wall enhancement on downstream collateral flow

BACKGROUND

The effect of arteriosclerotic intracranial arterial vessel wall enhancement (IAVWE) on downstream collateral flow found in vessel wall imaging (VWI) is not clear. Regardless of the mechanism underlying IAVWE on VWI, damage to the patient's nervous system caused by IAVWE is likely achieved by affecting downstream cerebral blood flow. The present study aimed to investigate the effect of arteriosclerotic IAVWE on downstream collateral flow.

METHODS

The present study recruited 63 consecutive patients at the Second Hospital of Hebei Medical University from January 2021 to November 2021 with underlying atherosclerotic diseases and unilateral middle cerebral artery (MCA) M1-segment stenosis who underwent an magnetic resonance scan within 3 days of symptom onset. The patients were divided into 4 groups according to IAVWE and the stenosis ratio (Group 1, n = 17; Group 2, n = 19; Group 3, n = 13; Group 4, n = 14), and downstream collateral flow was analyzed using three-dimensional pseudocontinuous arterial spin labeling (3D-pCASL) and RAPID software. The National Institutes of Health Stroke Scale (NIHSS) scores of the patients were also recorded. Two-factor multivariate analysis of variance using Pillai's trace was used as the main statistical method.

RESULTS

No statistically significant difference was found in baseline demographic characteristics among the groups. IAVWE, but not the stenosis ratio, had a statistically significant significance on the late-arriving retrograde flow proportion (LARFP), hypoperfusion intensity ratio (HIR), and NIHSS scores ( F = 20.941, P <0.001, Pillai's trace statistic = 0.567). The between-subject effects test showed that IAVWE had a significant effect on the three dependent variables: LARFP ( R2 = 0.088, F = 10.899, P = 0.002), HIR ( R2 = 0.234, F = 29.354, P <0.001), and NIHSS ( R2 = 114.339, F = 33.338, P <0.001).

CONCLUSIONS

Arteriosclerotic IAVWE significantly reduced downstream collateral flow and affected relevant neurological deficits. It was an independent factor affecting downstream collateral flow and NIHSS scores, which should be a focus of future studies.

TRIAL REGISTRATION

ChiCTR.org.cn, ChiCTR2100053661.

Current state and guidance on arterial spin labeling perfusion MRI in clinical neuroimaging

This article focuses on clinical applications of arterial spin labeling (ASL) and is part of a wider effort from the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group to update and expand on the recommendations provided in the 2015 ASL consensus paper. Although the 2015 consensus paper provided general guidelines for clinical applications of ASL MRI, there was a lack of guidance on disease-specific parameters. Since that time, the clinical availability and clinical demand for ASL MRI has increased. This position paper provides guidance on using ASL in specific clinical scenarios, including acute ischemic stroke and steno-occlusive disease, arteriovenous malformations and fistulas, brain tumors, neurodegenerative disease, seizures/epilepsy, and pediatric neuroradiology applications, focusing on disease-specific considerations for sequence optimization and interpretation. We present several neuroradiological applications in which ASL provides unique information essential for making the diagnosis. This guidance is intended for anyone interested in using ASL in a routine clinical setting (i.e., on a single-subject basis rather than in cohort studies) building on the previous ASL consensus review.

Arterial Spin Labeling-Based MRI Estimation of Penumbral Tissue in Acute Ischemic Stroke

BACKGROUND

Arterial spin labeling (ASL) has shown potential for the assessment of penumbral tissue in patients with acute ischemic stroke (AIS). The postlabeling delay (PLD) parameter is sensitive to arterial transit delays and influences cerebral blood flow measurements.

PURPOSE

To assess the impact of ASL acquisition at different PLDs for penumbral tissue quantification and to compare their performance regarding assisting patient selection for endovascular treatment with dynamic susceptibility contrast MRI (DSC-MRI) as the reference method.

STUDY TYPE

Retrospective.

POPULATION

A total of 53 patients (59.98 ± 12.60 years, 32% women) with AIS caused by internal carotid or middle cerebral artery occlusion.

FIELD STRENGTH/SEQUENCE

A 3-T, three-dimensional pseudo-continuous ASL with fast-spin echo readout.

ASSESSMENT

Hypoperfusion volume was measured using DSC-MRI and ASL with PLDs of 1.500 msec and 2.500 msec, respectively. Eligibility for endovascular treatment was retrospectively determined according to the imaging criteria of the Endovascular Therapy Following Imaging Evaluation for Ischemic Stroke trial (DEFUSE 3).

STATISTICAL TESTS

Kruskal-Wallis tests, Bland-Altman plots, Cohen's kappa, and receiver operating characteristic analyses were used. The threshold for statistical significance was set at P ˂ 0.05.

RESULTS

Hypoperfusion volume for ASL with a PLD of 1.500 msec was significantly larger than that for DSC-MRI, while the hypoperfusion volume for a PLD of 2.500 msec was not significantly different from that of DSC-MRI (P = 0.435). Bland-Altman plots showed that the mean volumetric error between the hypoperfusion volume measured by DSC-MRI and ASL with PLDs of 1.500/2.500 msec was -107.0 mL vs. 4.49 mL. Cohen's kappa was 0.679 vs. 0.773 for DSC-MRI and ASL, respectively, with a PLD of 1.500/2.500 msec. The sensitivity and specificity for ASL with a PLD of 1.500/2.500 msec in identifying patients eligible for treatment were 89.74% vs. 97.44% and 92.86% vs. 64.29%, respectively.

DATA CONCLUSION

In AIS, PLDs for ASL acquisition may have a considerable impact on the quantification of the hypoperfusion volume.

EVIDENCE LEVEL

3 TECHNICAL EFFICACY: Stage 2.

Effects of Post-Labeling Delay on Magnetic Resonance Evaluation of Brain Tumor Blood Flow Using Arterial Spin Labeling

We investigated the effect of post-labeling delay (PLD) on the evaluation of brain tumor blood flow using arterial spin labeling (ASL) magnetic resonance (MR) imaging to assess the need for imaging with two PLDs. Retrospective analysis was conducted on 63 adult patients with brain tumors who underwent contrast-enhanced MR imaging including ASL imaging with PLDs of both 1525 and 2525 ms on a 1.5 T or 3 T MR unit. Blood flow was estimated in the tumors and normal-appearing brain parenchyma, and tumor blood flow was normalized by parenchymal flow. Estimates of tumor blood flow, parenchymal flow, and normalized tumor flow showed no statistically significant differences between PLDs of 1525 and 2525 ms. Close correlations between different PLDs were found, with the closest correlation for normalized tumor flow. These results were similarly observed for the 1.5 T and 3 T units. The blood flow estimates obtained using ASL MR imaging in patients with brain tumors were highly concordant between PLDs of 1525 and 2525 ms, irrespective of the magnetic field strength. It is indicated that imaging with a single, standard PLD is acceptable for ASL assessment of brain tumor perfusion and that additional imaging with a long PLD is not required.

Association of fluid-attenuated inversion recovery vascular hyperintensity with ischaemic events in internal carotid artery or middle cerebral artery occlusion

BACKGROUND AND PURPOSE

Individuals with intracranial artery occlusion have high rates of ischaemic events and recurrence. It has been challenging to identify patients who had high-risk stroke using a simple, valid and non-invasive screening approach. This study aimed to investigate whether fluid-attenuated inversion recovery (FLAIR) vascular hyperintensity (FVH), a specific imaging sign on the FLAIR sequence, could be a predictor of ischaemic events in a population with internal carotid artery (ICA) or middle cerebral artery (MCA) occlusion.

METHODS

We retrospectively analysed 147 patients (mean 60.43±12.83 years) with 149 lesions, including 37 asymptomatic and 112 symptomatic cases of ICA or MCA occlusion. Symptomatic occlusion was considered if ischaemic events were present in the relevant territory within 90 days. FVH Alberta Stroke Program Early Computed Tomography Score (FVH-ASPECTS: 0-7, with 0 indicating absence of FVH and 7 suggesting prominent FVH) and collateral circulation grade were assessed for each participant. Multivariable logistic regression analysis was performed to detect independent markers associated with symptomatic status.

RESULTS

A lower FVH-ASPECTS was associated with a more favourable collateral circulation grade (rho=-0.464, p<0.0001). The FVH-ASPECTS was significantly lower in the asymptomatic occlusion group than in the symptomatic occlusion group (p<0.0001). FVH-ASPECTS (Odd ratio, 2.973; 95% confidence interval, 1.849 to 4.781; p<0.0001) was independently associated with symptomatic status after adjustment for age, sex, lesion location and collateral circulation grade in the multivariate logistic regression. The area under the curve was 0.861 for the use of FVH-ASPECTS to identify symptomatic occlusion.

CONCLUSIONS

The ability to discriminate symptomatic from asymptomatic occlusion suggests that FVH may be a predictor of stroke. As a simple imaging sign, FVH may serve as a surrogate for haemodynamic impairments and can be used to identify high-risk stroke cases early in ICA or MCA occlusion.

Collateral-Core Ratio as a Novel Predictor of Clinical Outcomes in Acute Ischemic Stroke

The interaction effect between collateral circulation and ischemic core size on stroke outcomes has been highlighted in acute ischemic stroke (AIS). However, biomarkers that assess the magnitude of this interaction are still lacking. We aimed to present a new imaging marker, the collateral-core ratio (CCR), to quantify the interaction effect between these factors and evaluate its ability to predict functional outcomes using machine learning (ML) in AIS. Patients with AIS caused by anterior circulation large vessel occlusion (LVO) were recruited from a prospective multicenter study. CCR was calculated as collateral perfusion volume/ischemic core volume. Functional outcomes were assessed using the modified Rankin Scale (mRS) at 90 days. An ML model was built and tested with a tenfold cross-validation using nine clinical and four imaging variables with mRS score 3-6 as unfavorable outcomes. Among 129 patients, CCR was identified as the most important variable. The prediction model incorporating clinical factors, ischemic core volume, collateral perfusion volume, and CCR showed better discriminatory power in predicting unfavorable outcomes than the model without CCR (mean C index 0.853 ± 0.108 versus 0.793 ± 0.133, P = 0.70; mean net reclassification index 52.7% ± 32.7%, P < 0.05). When patients were divided into two groups based on their CCR value with a threshold of 0.73, unfavorable outcomes were significantly more prevalent in patients with CCR ≤ 0.73 than in those with CCR > 0.73. CCR is a robust predictor of functional outcomes, as identified by ML, in patients with acute LVO. The prediction model that incorporated CCR improved the model's ability to identify unfavorable outcomes. ClinicalTrials.gov Identifier: NCT02580097.

Laser speckle contrast imaging for blood flow monitoring in predicting outcomes after cerebral ischemia-reperfusion injury in mice

BACKGROUND

In the treatment of ischemic cerebral stroke (ICS), most conventional treatments, including carotid endarterectomy and carotid artery stenting, may cause cerebral ischemia-reperfusion injury (CIRI). For treated ICS patients, changes in cerebral blood flow are directly related to brain function. At present, computed tomography perfusion, dynamic susceptibility contrast-enhanced perfusion weighted imaging and magnetic resonance arterial spin labeling perfusion imaging are used to monitor cerebral blood flow, but they still have some limitations. Our study aimed to monitor the changes in cerebral cortical blood flow by laser speckle contrast imaging (LSCI) in CIRI model mice and to propose a new method for predicting outcomes after CIRI. C57BL/6 N mice were used to establish a mouse CIRI model based on a modified thread-occlusion method and divided into a good outcome group and a poor outcome group according to survival within 7 days. The cerebral cortical blood flow of the area supplied by the left middle cerebral artery was monitored by LSCI at baseline (before modeling), 1 h after ischemia, immediately after reperfusion and 24 h after reperfusion. Then, the brains of the mice were removed immediately and stained with hematoxylin and eosin to observe the pathological changes in brain neurons.

RESULTS

The cerebral cortical blood flow in the poor outcome group was obviously reduced compared with that less in the good outcome group at 24 h after reperfusion (180.8 ± 20.9 vs. 113.9 ± 6.4, p = 0.001), and at 24 h after reperfusion, the cerebral cortical blood flow was negatively correlated with the severity of brain tissue injury (p = - 0.710, p = 0.010).

CONCLUSIONS

LSCI can monitor the changes in cerebral cortical blood flow during CIRI in mice and could be used as a feasible method for predicting outcomes after CIRI in mice.

Pseudo-continuous arterial spin labeling with short post-labeling delay time sensitively reflects the hemodynamics of symptomatic patients with permanent large vessel occlusion before and after revascularization

BACKGROUND AND PURPOSE

This study evaluated the feasibility of arterial spin labeling (ASL) for diagnosing hemodynamic stroke due to permanent anterior circulation large vessel occlusion.

METHODS

Three-dimensional pseudo-continuous ASL data at two post-labeling delay (PLD) times (1.5 and 2.5 s) in patients with unilateral permanent middle cerebral artery (MCA) segment 1 (M1) or internal cerebral artery (ICA) occlusion were acquired during routine magnetic resonance angiography. Sixty-one patients with symptomatic occlusion (M1, 24; ICA, 37) and 69 patients with asymptomatic occlusion (M1, 21; ICA, 48) were enrolled. Regions of interest were automatically placed in the MCA region using a template. The respective scans were compared with asymptomatic M1 or ICA occlusion scans. The ratio of signal intensity (occlusion side/non-occlusion side) in the perfusion area of MCA (asymmetry index [AI]) was compared between both groups.

RESULTS

In both PLD groups, AI was significantly lower in symptomatic patients than in asymptomatic patients. The receiver operating characteristic curve showed moderate capacity for the prediction of symptomatic AI in both groups (area under the curve, 0.739 and 0.712, respectively). As a result of extracranial-intracranial bypass operation in 28 symptomatic (M1, eight; ICA, 20) patients, AI was significantly higher postoperatively in the PLD 1.5 s group than in the PLD 2.5 s group.

CONCLUSION

In symptomatic patients with permanent large vessel occlusion, the signal intensity ratio of pseudo-continuous ASL with short PLD sensitively reflects the hemodynamics before and after revascularization; therefore, this technique may be an alternative method in situations where PET or SPECT cannot be performed.

Collateral circulation detected by arterial spin labeling predicts outcome in acute ischemic stroke

BACKGROUND

Robust collateral circulation is strongly associated with good outcomes in acute ischemic stroke (AIS).

AIMS

To determine whether collateral circulation detected by arterial spin labeling (ASL) magnetic resonance imaging could predict good clinical outcome in AIS patients with 90 days follow-up.

MATERIALS AND METHODS

Total 58 AIS patients with anterior circulation stroke were recruited. Collateral circulation was defined as arterial transit artifact in ASL images. Modified Rankin Scale (mRS), the Barthel Index, and National Institutes of Health Stroke Scale (NIHSS) were employed to evaluate neurological function for the baseline and 90 days follow-up. The percent changes of these scores were also calculated, respectively. Finally, a support vector classifier model of machine learning and receiver operating characteristic curve were employed to estimate the power of ASL collaterals (ASLcs) predicting the clinical outcome.

RESULTS

Patients with ASLcs represented higher rate of good outcome (83.30% vs. 31.25%, p < .001) and lower follow-up mRS scores (p < .001), when compared to patients without ASLcs. There were significant differences for percent changes of mRS scores and NIHSS scores between these two groups. Further, the presence of ASLcs could predict good clinical outcome (OR, 1.54; 95% CI, 1.10-2.16), even after controlling for baseline NIHSS scores. The SVC model incorporating baseline NIHSS scores and ASLcs had significant predictive effect (accuracy, 79.3%; AUC, 0.806) on clinical prognosis for AIS patients.

DISCUSSION

We targeted on the non-invasive assessment of collateral circulation using ASL technique and found that patients with ASLcs were more likely to have a good clinical outcome after AIS. This finding is of guiding significance for treatment selection and prognostic prediction.

CONCLUSIONS

Early ASLcs assessment provides a good powerful tool to predict clinical outcome for AIS patients with 90 days follow-up.

Baseline Hemodynamic Impairment and Revascularization Outcome in Newly Diagnosed Adult Moyamoya Disease Determined by Pseudocontinuous Arterial Spin Labeling

OBJECTIVE

The study aimed to investigate the hemodynamic features and independent predictors of neoangiogenesis after revascularization in moyamoya disease (MMD) by pseudocontinuous arterial spin labeling magnetic resonance imaging (pCASL MRI).

METHODS

Thirty-nine MMD patients were categorized into infarction group, hemorrhagic group, and atypical group. All patients underwent combined bypass surgery and pCASL MRI with postlabeling delays (PLD) of 1525 ms and 2525 ms. Absolute CBF_MCA (cerebral blood flow in middle cerebral artery territory), relative CBF_MCA (CBF_MCA 2525 ms/CBF_MCA 1525 ms), and spatial coefficient of variation of MCA (CoV_MCA) were analyzed. Relationships between CBF_MCA and the following clinical parameters were assessed: Suzuki stage, modified Rankin scale (mRS), cerebrovascular accident lesion score, and deep medullary veins score. Potential predictors for favorable neoangiogenesis and hemodynamic changes were explored as well.

RESULTS

Preoperative CBF_MCA differed among MMD patients with variable clinical presentations, Matsushima stages, modified Rankin Scale scores, CVA scores, and deep medullary vein scores. After bypass surgery, mean CBF_MCA increased significantly in the infarction group (P = 0.027) and decreased in the hemorrhagic group (P = 0.043), while spatial CoV_MCA was observed to decline in all groups. Higher preoperative relative CBF_MCA and spatial CoV_MCA were independent predictors for robust neoangiogenesis after bypass. The cutoff value of 0.330 of spatial CoV_MCA at long PLD yielded the best sensitivity at 82.1% and specificity at 81.8%. Furthermore, both preoperative relative CBF_MCA and spatial CoV_MCA showed mild positive correlations with ΔmRS in MMD patients.

CONCLUSIONS

pCASL-MRI with multiple PLDs could reflect preoperative hemodynamic impairment and predict the neoangiogenesis after combined bypass surgery in moyamoya patients.

The value of whole-brain CT perfusion imaging combined with dynamic CT angiography in the evaluation of pial collateral circulation with middle cerebral artery occlusion

BACKGROUND

Middle cerebral artery (MCA) occlusion is extremely common, especially unilateral artery, which can result in a significant incidence of cerebral infarction.

OBJECTIVE

To assess the value of whole-brain computed tomography perfusion (CTP) imaging combined with dynamic CT angiography (dCTA) in the evaluation of pial collateral circulation in patients with MCA occlusion.

METHODS

Whole-brain CTP and dCTA images were acquired in 58 patients with unilateral MCA occlusion. All patients were divided into three groups according to the American Society of Interventional and Therapeutic Neuroradiology/Society of Interventional Radiology (ASITN/SIR) collateral score (by CTA). The CTP parameters were analysed, including relative cerebral blood flow (rCBF), relative cerebral blood volume (rCBV), relative mean transit time (rMTT), and relative time to peak (rTTP). Patients were followed up with the modified Rankin scale (mRS). All cases in this study were confirmed by DSA.

RESULTS

The CTP parameters of the MCA blood supply area on the affected side of patients with different degrees of stenosis were significantly different from those on the unaffected side. There are significant differences in the CTP parameters and openings of the Willis circle in patients with different degrees of stenosis. Significant differences were found in the number of patients with good prognosis.

CONCLUSIONS

Whole-brain CT perfusion combined with dynamic CTA can structurally and functionally evaluate the establishment of pial collateral circulation and its effect on cerebral hemodynamic changes.

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.

Clinical utility of arterial spin labeling perfusion images in the emergency department for the work-up of stroke-like symptoms

PURPOSE

To assess the utility of ASL in evaluating patients presenting to the ED with stroke-like symptoms.

METHODS

ASL and DWI images from 526 consecutive patients presenting to the ED with acute stroke symptoms were retrospectively reviewed. DWI images were evaluated for volume of restricted diffusion using ABC/2. ASL maps were evaluated for decreased, normal, or increased signal. The volume of decreased ASL signal was calculated using the same ABC/2 technique. The volume of decreased ASL signal was correlated with the volume of DWI signal abnormality to identify cases of mismatch (DWI:ASL ratio > 1.8) and to correlate this mismatch with infarct growth on imaging follow-up. NIHSS, length of hospital stay, mRS, and future admission for acute stroke-like symptoms were recorded. Correlations between ASL abnormalities and clinical parameters were evaluated using a two-tailed t-test.

RESULTS

Of the 526 patients presenting with acute stroke symptoms, 136 patients had an abnormal ASL scan and 388 patients had a normal ASL scan. Of the 136 patients with abnormal ASL, 84 patients had low ASL signal with 79 of these being related to acute infarcts. Elevated ASL signal was seen in 52 patients, of which 30 of these patients had reperfusion hyperemia related to acute infarctions. ASL had a negative predictive value of 94% for evaluating patients with acute ischemic stroke. A subset of patients with abnormal ASL scans with a discharge diagnosis of acute infarction were found to have an ASL:DWI mismatch (ratio > 1.8) and demonstrated significant lesion growth on follow-up imaging (57%). This included some patients who exhibited low ASL signal before development of diffusion restriction (infarction).

CONCLUSION

In patients presenting to the ED with acute stroke symptoms, ASL provides information not available with DWI alone. The NPV of ASL for evaluating patients with acute ischemia was 94%.

Perfusion Defects and Collateral Flow Patterns in Acute Small Subcortical Infarction: a 4D Dynamic MRI Study

The hemodynamic changes of acute small subcortical infarction (SSI) are not well understood. We evaluate the hemodynamic changes and collaterals in acute SSI using perfusion magnetic resonance imaging (MRI). A total of 103 patients with acute SSI in penetrating artery territories were recruited and underwent MRI within 24 h of stroke onset. Using 4D dynamic perfusion MRI, they were divided into three patterns: 25 (24%) with normal perfusion, 31 (30%) with compensated perfusion, and 47 (46%) with hypoperfusion. The development of anterograde or retrograde collaterals was also evaluated. Patients with hypoperfusion pattern had the highest rate of early neurological deterioration (32%, p = 0.007), the largest initial and final infarction volumes (p < 0.001 and p = 0.029), the lowest relative cerebral blood flow (0.63, p < 0.001), and the lowest rate of anterograde and retrograde collaterals (19%, p < 0.001; 66%, p = 0.002). The anterograde collaterals were associated with higher relative cerebral blood volume (0.91 vs. 0.77; p = 0.024) and a higher rate of deep cerebral microbleeds (48 vs. 21%; p = 0.028), whereas retrograde collaterals were associated with higher systolic and diastolic blood pressure (p = 0.031 and 0.020), smaller initial infarction volume (0.81 vs. 1.34 ml, p = 0.031), and a higher rate of lobar cerebral microbleeds (30 vs. 0%; p = 0.013). Both anterograde and retrograde collaterals may play a critical role in maintaining cerebral perfusion and can have an impact on patient clinical outcomes. Further studies are warranted to verify these findings and to investigate effective treatments.

Early Neurological Deterioration and Hypoperfusion Volume Ratio on Arterial Spin Labeling in Patients with Acute Ischemic Stroke

BACKGROUND

Arterial spin labeling (ASL) is a magnetic resonance imaging (MRI) technique used to quantify cerebral blood perfusion by labeling blood water as it flows throughout the brain. Hypoperfusion volume ratio (HVR) can be calculated using proportional hypoperfusion volume on ASL-based cerebral blood flow (CBF). This study aimed to explore the relation between HVR and early neurological deterioration (END) in AIS patients.

SUBJECTS AND METHODS

Patients with AIS were recruited consecutively, and ASL and regular MRI scans were performed. HVR was calculated from 1.5 and 2.5s post labeling delay (PLD) ASL-CBF maps. END was defined as ≥2 points increment of NIHSS within 72 hours of stroke onset. Univariate and multivariate analysis were used to evaluate the relation between HVR and END. Receiver operating characteristic (ROC) curves were used to determine the ability of HVR in predicting END.

RESULTS

Of the 52 enrolled patients, 18 (34.5%) were determined with END. In patients with END, the median hypoperfusion volume was 20 mL [Inter Quartile Range)IQR, 6-72.5 mL] at 1.5s PLD, and 11.2 mL (IQR, 5.3-26 mL) at 2.5s PLD; Sixteen (88.9%) patients had HVR ≥50%, and 13 (72.2%) patients hypoperfusion volume at 2.5s PLD ASL were greater than diffusion-weighted imaging (DWI) infarct volume. In patients without END, median hypoperfusion volume was 7 mL (IQR, 4-30 mL) at 1.5s PLD, and 4 mL (IQR, 1.5-8.5 mL) at 2.5s; Eleven (32.4%) patients had HVR ≥50%, and 10 (29.4%) patients hypoperfusion volume at 2.5s PLD ASL were greater than DWI infarct volume. The proportion of HVR ≥50% and hypoperfusion volume >DWI infarct volume were more frequent in patients with END than patients without (all P<0.001). After adjusted for age, admission NIHSS, proportion of hypoperfusion volume > DWI infarct and arterial transit artifact (ATA) by logistic regression analysis, HVR ≥50% (OR=13.1, P=0.003) was an independent risk factor for END. ROC analysis demonstrated that the HVR could predict END with an area under the curve of 0.794 (P=0.001).

CONCLUSIONS

HVR obtained from the 1.5 and 2.5s PLD ASL may be a useful predictor of END in AIS. The value of HVR may be a marker for hemodynamic impairments.

Ivy Sign in Moyamoya Disease: A Comparative Study of the FLAIR Vascular Hyperintensity Sign Against Contrast-Enhanced MRI

BACKGROUND AND PURPOSE

The ability of the ivy sign on contrast-enhanced T1-weighted MR imaging (CEMR) to reflect cerebral perfusion and postoperative revascularization in Moyamoya disease remains largely unknown. We aimed to compare the capabilities of CEMR and FLAIR.

MATERIALS AND METHODS

CEMR, FLAIR, arterial spin-labeling, and DSA were performed in 44 patients with Moyamoya disease. The ivy sign was scored separately on CEMR and FLAIR using the Alberta Stroke Program Early CT Score. The status of leptomeningeal collaterals was scored on DSA. The postoperative Matsushima grade was evaluated at least 3 months after surgical revascularization.

RESULTS

Scoring of the ivy sign on CEMR showed excellent interrater reliability, and FLAIR vascular hyperintensity showed moderate interrater reliability. Correlation analyses revealed that DSA scores were more consistent with the CEMR-based ivy sign score (r = 0.25, P = .03) than with FLAIR vascular hyperintensity (r = 0.05, P = .65). The CEMR-based ivy sign score was significantly correlated with CBF in late-Suzuki stage Moyamoya disease (t = -2.64, P = .02). The CEMR-based ivy sign score at baseline was significantly correlated with the postoperative Matsushima grade (r = 0.48, P = .03).

CONCLUSIONS

In this study, CEMR outperformed FLAIR in capturing the ivy sign in Moyamoya disease. In addition, the CEMR-based ivy sign score provided adequate information on hemodynamic status and postoperative neovascularization. The current study suggested that CEMR could be considered as an alternative to FLAIR in future studies investigating leptomeningeal collaterals in Moyamoya disease.

Ocular Blood Flow Measurements in Diabetic Retinopathy Using 3D Pseudocontinuous Arterial Spin Labeling

BACKGROUND

Distinguishing between the two broad categories of diabetic retinopathy (DR), nonproliferative DR (NPDR) and proliferative DR (PDR), is significant, as the therapeutic strategies for each are completely different.

PURPOSE

To characterize the ocular blood flow (OBF) of DR patients and evaluate the potential utility of OBF values in categorizing DR.

STUDY TYPE

Prospective.

SUBJECTS

A total of 41 DR patients (82 eyes) were recruited in our study. Group 1 comprised 48 eyes with NPDR, and Group 2 comprised 34 eyes with PDR.

FIELD STRENGTH/SEQUENCE

3D pseudocontinuous arterial spin labeling (3D-pcASL) with two postlabeling delays (PLDs) was acquired at 3.0T MR.

ASSESSMENT

OBF values were independently obtained by two doctors from the OBF map.

STATISTICAL TESTS

OBF values and clinical characteristics were compared between the groups using two-sample t-tests and chi-square tests. Receiver operating characteristic (ROC) curves were obtained, and the area under the curve (AUC) was calculated. The consistency of OBF values reported by the two doctors was evaluated using the intraclass correlation coefficient (ICC).

RESULTS

OBF values at PLDs of 1.5 seconds and 2.5 seconds were significantly lower in Group 2 than in Group 1 (P < 0.05 for both PLDs). The OBF values of Group 2 showed a greater increase than those of Group 1 from PLD 1.5 to 2.5 seconds. The AUC of OBF at the 1.5 seconds PLD was 0.90, with a cutoff of 7.73 mL/min/100 g, and the AUC of the OBF at the 2.5 seconds PLD was 0.75, with a cutoff of 8.44 mL/min/100 g. The ICC between the two observers was 0.844 for the OBF at 1.5 seconds PLD and 0.872 for the OBF at 2.5 seconds PLD.

DATA CONCLUSION

PDR can be differentiated from NPDR by the value of OBF as measured by 3D-pcASL.

LEVEL OF EVIDENCE

1 TECHNICAL EFFICACY STAGE: 1.

On the Validation of a Multiple-Network Poroelastic Model Using Arterial Spin Labeling MRI Data

The Multiple-Network Poroelastic Theory (MPET) is a numerical model to characterize the transport of multiple fluid networks in the brain, which overcomes the problem of conducting separate analyses on individual fluid compartments and losing the interactions between tissue and fluids, in addition to the interaction between the different fluids themselves. In this paper, the blood perfusion results from MPET modeling are partially validated using cerebral blood flow (CBF) data obtained from arterial spin labeling (ASL) magnetic resonance imaging (MRI), which uses arterial blood water as an endogenous tracer to measure CBF. Two subjects—one healthy control and one patient with unilateral middle cerebral artery (MCA) stenosis are included in the validation test. The comparison shows several similarities between CBF data from ASL and blood perfusion results from MPET modeling, such as higher blood perfusion in the gray matter than in the white matter, higher perfusion in the periventricular region for both the healthy control and the patient, and asymmetric distribution of blood perfusion for the patient. Although the partial validation is mainly conducted in a qualitative way, it is one important step toward the full validation of the MPET model, which has the potential to be used as a testing bed for hypotheses and new theories in neuroscience research.

Perfusion and plaque evaluation to predict recurrent stroke in symptomatic middle cerebral artery stenosis

Background and purpose

We investigated the baseline demographics of patients with severe unilateral atherosclerotic stenosis of the middle cerebral artery (MCA) using multimodal MRI and evaluated the haemodynamic impairments and plaque characteristics of patients who had a recurrent stroke.

Materials and methods

We retrospectively recruited consecutive patients with severe unilateral atherosclerotic MCA stenosis who underwent arterial spin labelling (ASL) with postlabelling delay (PLD) of 1.5 and 2.5 s, and vessel wall MRI. For each PLD, cerebral blood flow (CBF) maps were generated. Hypoperfusion volume ratio (HVR) from 2 PLD CBF was calculated. An HVR value ≥50% was considered as severe HVR. Plaque areas, plaque burden, plaque length and remodelling index were measured. Plaque enhancement at maximal lumen narrowing site were graded. Baseline clinical and imaging characteristics were compared between patients with (event+) and without (event−) 1 year ischaemic events.

Results

Forty-three patients (47.23±12.15 years; 28 men) were enrolled in this study. Seven patients had an HVR ≥50%. During the 1-year follow-up, 7 patients had experienced a recurrent stroke. HVR were significantly higher in the event+ than event− (53.17%±29.82% vs 16.9%±15.57%, p=0.0002), whereas no significant difference was detected in plaque areas, plaque burden, remodelling index, plaque length and plaque enhancement grade. The multivariable analysis revealed that a severe HVR was significantly associated with a recurrent stroke (Odds ratio=12.93, 95% confidence interval 1.57 to 106.24, p=0.017) after adjusted by hypertension and smoking.

Conclusion

HVR obtained from two PLD ASL may be a useful imaging predictor of recurrent stroke.

Longitudinal assessment of cerebral blood flow changes following carotid artery stenting and endarterectomy

BACKGROUND

Carotid artery stenting (CAS) and endarterectomy (CEA) are major treatment strategies for patients with internal carotid artery (ICA) stenosis; however, the dynamic cerebral blood flow (CBF) changes after CAS and CEA remain unclear.

PURPOSE

This study aimed to monitor consecutive CBF changes at 24-h intervals in patients who underwent CAS and CEA to explore the potential pattern of CBF alternation and compare the effect on CBF changes of different surgical methods.

METHODS

Thirty-two patients (28 males and 4 females; age = 63.0 ± 7.3 years) with 70-99% ipsilateral stenosis in the ICA were enrolled, of which 19 underwent CAS and 13 underwent CEA by prospective cross-sectional study. Routine head MRI and three-dimensional pseudo-continuous arterial spin labeling were performed using a 3.0-T system within 7 days prior to operations, and at 4 consecutive time-points (24, 48, 72, and 96 h) after operations. Comparisons within groups were made using paired t test, and comparisons between groups were made using independent-sample t test.

RESULTS

The CBF values markedly increased at 24 h after CAS and CEA (P < 0.05) compared with baseline. Most patients showed peak CBF values on the ipsilateral side at 72 h (13/19, 68%) after CAS and at 48 h (10/13, 77%) after CEA, which then declined. The CBF values for the ipsilateral ICA territory of CEA group were higher than those of CAS group at 24, 48, 72, and 96 h (P < 0.05).

CONCLUSIONS

The pattern of dynamic CBF changes is different after CAS and CEA, which may be helpful for the improvement of the patient's postoperative management.

Collateral perfusion using arterial spin labeling in symptomatic versus asymptomatic middle cerebral artery stenosis

The purpose was to assess the difference of collaterals in symptomatic versus asymptomatic patients with unilateral middle cerebral artery (MCA) stenosis by comparing cerebral blood flow (CBF) at two post labeling delays (PLD) using three-dimensional pseudo-continuous arterial spin labeling (3D pCASL). Eighty-one patients (49 symptomatic and 32 asymptomatic) with unilateral MCA stenosis ≥50% who underwent pCASL with two PLDs were included. Mean CBF and CBF subtraction images between two PLDs of MCA territories were compared in symptomatic and asymptomatic groups, respectively. Compared with the asymptomatic group, patients with symptomatic MCA stenosis had significantly lower CBF in the MCA territory of stenotic side at each PLD. The CBF of stenotic territory showed greater increase than that of normal side from PLD 1.5 to 2.5 s. The CBF of asymptomatic MCA territory increased similarly with that of symptomatic MCA territory from PLD of 1.5 to 2.5 s in stenotic side, while symptomatic patients experienced significantly slower antegrade flow. On CBF subtraction images, asymptomatic patients showed larger volume of differences between PLD of 1.5 and 2.5 s compared with those of symptomatic patients ( p = 0.037). The results suggest that more robust collateral perfusion on two-delay 3D pCASL is present in asymptomatic patients compared with symptomatic patients.

Advanced Neuroimaging of Acute Ischemic Stroke: Penumbra and Collateral Assessment

Acute ischemic stroke (AIS) occurs when there is a sudden loss in cerebral blood flow due to embolic or thromboembolic occlusion of a cerebral or cervical artery. Patients with AIS require emergent neuroimaging to guide treatment, which includes intravenous thrombolysis and endovascular mechanical thrombectomy (EMT). Recent advances in AIS treatment by EMT has been driven in part by advances in computed tomography (CT) and MR imaging neuroimaging evaluation of ischemic penumbra and pial collateral vessels. The authors review advanced noninvasive brain imaging by CT and MR imaging for the evaluation of AIS focusing on penumbral and collateral imaging.

Timely Visualization of the Collaterals Formed during Acute Ischemic Stroke with Fe3 O4 Nanoparticle-based MR Imaging Probe

Ischemic stroke is one of the major leading causes for long-term disability and mortality. Collateral vessels provide an alternative pathway to protect the brain against ischemic injury after arterial occlusion. Aiming at visualizing the collaterals occurring during acute ischemic stroke, an integrin α_v β₃ -specific Fe₃ O₄ -Arg-Gly-Asp (RGD) nanoprobe is prepared for magnetic resonance imaging (MRI) of the collaterals. Rat models are constructed by occluding the middle cerebral artery for imaging studies of cerebral ischemia and ischemia-reperfusion on 7.0 Tesla MRI using susceptibility-weighted imaging sequence. To show the binding specificity to the collaterals, the imaging results acquired with the Fe₃ O₄ -RGD nanoprobe and the Fe₃ O₄ mother nanoparticles, respectively, are carefully compared. In addition, an RGD blocking experiment is also carried out to support the excellent binding specificity of the Fe₃ O₄ -RGD nanoprobe. Following the above experiments, cerebral ischemia-reperfusion studies show the collateral dynamics upon reperfusion, which is very important for the prognosis of various revascularization therapies in the clinic. The current study has, for the first time, enabled the direct observation of collaterals in a quasi-real time fashion and further disclosed that the antegrade flow upon reperfusion dominates the blood supply of primary ischemic tissue during the early stage of infarction, which is significantly meaningful for clinical treatment of stroke.

Could Arterial Spin Labeling Distinguish Patients in Minimally Conscious State from Patients in Vegetative State?

Purpose

Diagnostic error is common among patients with vegetative state (VS) and minimally conscious state (MCS). The purpose of this article is to use three-dimensional pseudo-continuous arterial spin labeling (pcASL) to compare cerebral blood flow (CBF) patterns in patients in MCS with those in VS.

Methods

Patients meeting MCS and VS criteria were identified. Two post-labeling delay (PLD) time pcASL on 3.0-Tesla magnetic resonance imaging scanner system were performed with patients in the resting awake state. After registration to T1WI structure imaging, multiple brain regions of interest of ASL CBF map were automatically separated. The average CBF value of every brain region was calculated and compared between the MCS and VS groups with t-tests.

Results

Fifteen patients with VS were identified, with ages ranging from 33 to 71 years. Eight patients who met the MCS criteria ranged in age from 23 to 61 years. Compared with VS, the regional CBF for MCS had a pattern of significantly increased CBF in the regions including the putamen, anterior cingulate gyrus, and medial frontal cortex. A left-lateralized pattern was observed to differentiate MCS from VS. CBF with PLD 2.5 s could find more regions of pattern differentiating MCS from VS than with PLD 1.5 s, except for the pallidum.

Conclusion

MCS might be differentiated from VS by different ranges of regional CBF as measured by ASL. Multi-PLD ASL may serve as an adjunct method to separate MCS from VS and assess functional reserve in patients recovering from severe brain injuries.

Multi-delay ASL can identify leptomeningeal collateral perfusion in endovascular therapy of ischemic stroke

BACKGROUND AND PURPOSE

Multi-delay arterial spin-labeling (ASL) perfusion imaging has been used as a promising modality to evaluate cerebral perfusion. Our aim was to assess the association of leptomeningeal collateral perfusion scores based on ASL parameters with outcome of endovascular treatment in patients with acute ischemic stroke (AIS) in the middle cerebral artery (MCA) territory.

MATERIALS AND METHODS

ASL data at 4 post-labeling delay (PLD) times (PLD = 1.5, 2, 2.5, 3 s) were acquired during routine clinical magnetic resonance examination on AIS patients prior to endovascular treatment. A 3-point scale of leptomeningeal collateral perfusion grade on 10 anatomic regions was determined based on arterial transit times (ATT), cerebral blood flow (CBF), and arterial cerebral blood volume (CBV), estimated by the multi-delay ASL protocol. Based on a 90-day modified Rankin Scale (mRS), the patients were dichotomized to moderate/good (mRS 0-3) and poor outcome (mRS 4-6) and the regional collateral flow scores were compared.

RESULTS

Fifty-five AIS patients with unilateral MCA stroke (mean 73.95±14.82 years) including 23 males were enrolled. Compared with poor outcome patients, patients with moderate to good outcomes had a significantly higher leptomeningeal collateral perfusion scores on CBV (3.01±2.11 vs. 1.82±1.51, p=0.024) but no differences on scores on CBF (2.31±1.61 vs. 1.66±1.32, p=0.231) and ATT (2.67±2.33 vs. 3.42±3.37, p=0.593).

CONCLUSIONS

Higher leptomeningeal collateral perfusion scores on CBV images by ASL may be a specific marker of clinical outcome after endovascular treatment in patients with acute MCA ischemic stroke. Further study with larger sample size is warranted.

Clinical usefulness of multiphase arterial spin labeling imaging for evaluating cerebral hemodynamic status in a patient with symptomatic carotid stenosis by comparison with single-photon emission computed tomography: A case study

Multiphase arterial spin labeling (ASL), which obtains the imaged slices with various postlabeling delays, allows for the noninvasive assessment of cerebral hemodynamics that cannot be adequately acquired by single-photon emission computed tomography (SPECT) imaging. We describe the clinical usefulness of multiphase ASL in a patient with symptomatic carotid stenosis by comparison with SPECT at rest using iodoamphetamine. A 75-year-old man was referred to our hospital with severe stenosis of the left internal carotid artery (ICA). While SPECT showed no significant laterality of cerebral blood flow (CBF), multiphase ASL demonstrated relatively delayed perfusion in the left ICA territory. The patient underwent stent placement for the left ICA stenosis. Postoperatively, while SPECT demonstrated no significant laterality of CBF, multiphase ASL revealed improved perfusion in the left ICA territory. This case showed that multiphase ASL could accurately evaluate the cerebral hemodynamic status which could not be detected using pre- and postoperative SPECT.

The role of neuroimaging in elucidating the pathophysiology of cerebral ischemia

Neuroimaging provides detailed information regarding the hemodynamic, metabolic and cellular parameters of cerebral ischemia (CI). Although providing just a snapshot in time, it assists in delineating the boundaries and extent of this continually evolving process, from the irreversibly damaged infarct core to the penumbral tissue, where salvage via reperfusion has been the focus of acute stroke therapies. Beyond the extent of the ischemic lesion, neuroimaging elucidates the topography and underlying mechanism of CI. Finally, based on the pathophysiological information, neuroimaging assists in the selection of optimal therapeutic strategies, from hyperacute to chronic phases of CI. Here we review different neuroimaging techniques by which the pathophysiology of cerebral ischemia can be delineated. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Sequential changes of arterial spin-labeling perfusion MR images with dual postlabeling delay following reconstructive surgery for giant internal carotid artery aneurysm

BACKGROUND

Arterial spin-labeling magnetic resonance perfusion imaging (ASL-MRI) allows noninvasive measurement of cerebral blood flow (CBF) but depends on arterial transit time (ATT). To overcome this problem, we developed a simple ASL technique with dual postlabeling delay (PLD) settings. In addition to the routinely used PLD of 1.5 seconds, we selected another PLD of 2.5 seconds to assess slowly streaming blood flow and detect arterial transit artifacts (ATAs) resulting from stagnant intravascular magnetically labeled spins.

CASE DESCRIPTION

We validated the dual PLD method with digital subtraction angiography (DSA) findings in a patient with an unruptured right giant internal carotid artery (ICA) aneurysm who underwent proximal ligation of the right cervical ICA followed by right superficial temporal artery-middle cerebral artery anastomosis. The giant aneurysm was detected as a strongly hyperintense signal area of ATA using both values of PLD. Decreased signal in the right hemisphere at PLD 1.5 seconds was somewhat improved at PLD 2.5 seconds. DSA revealed that this laterality resulted from the different ATT values between hemispheres due to stagnation of the labeled spin within the aneurysm. Postoperatively, with gradual but complete thrombosis and regression of the aneurysm, the size of the ASL hyperintense signal area decreased markedly. At postoperative 2 years, the aneurysm was not demonstrated as an ATA; furthermore, the decreased signals in the right hemisphere at PLD 1.5 seconds had mostly improved.

CONCLUSION

Serial ASL-MRI with dual PLDs could show dynamic changes of giant aneurysms and the associated hemodynamic state following the surgery.

The cerebral collateral circulation: Relevance to pathophysiology and treatment of stroke

The brain's collateral circulation consists of arterial anastomotic channels capable of providing nutrient perfusion to brain regions whose normal sources of flow have become compromised, as occurs in acute ischemic stroke. Modern CT-based neuroimaging is capable of providing detailed information as to collateral extent and sufficiency and is complemented by magnetic resonance-based methods. In the present era of standard-of-care IV thrombolysis for acute ischemic stroke, and following the recent therapeutic successes of randomized clinical trials of acute endovascular intervention, the sufficiency of the collateral circulation has been convincingly established as a key factor influencing the likelihood of successful reperfusion and favorable clinical outcome. This article reviews the features of the brain's collateral circulation; methods for its evaluation in the acute clinical setting; the relevance of collateral circulation to prognosis in acute ischemic stroke; the specific insights into the collateral circulation learned from recent trials of endovascular intervention; and the major influence of genetic factors. Finally, we emphasize the need to develop therapeutic approaches to augment collateral perfusion as an adjunctive strategy to be employed along with, or prior to, thrombolysis and endovascular interventions, and we highlight the possible potential of inhaled nitric oxide, albumin, and other approaches. This article is part of the Special Issue entitled 'Cerebral Ischemia'.

Noninvasive Evaluation of CBF and Perfusion Delay of Moyamoya Disease Using Arterial Spin-Labeling MRI with Multiple Postlabeling Delays: Comparison with 15O-Gas PET and DSC-MRI

BACKGROUND AND PURPOSE

Arterial spin-labeling MR imaging with multiple postlabeling delays has a potential to evaluate various hemodynamic parameters. To clarify whether arterial spin-labeling MR imaging can identify CBF and perfusion delay in patients with Moyamoya disease, we compared arterial spin-labeling, DSC, and ¹⁵O-gas PET in terms of their ability to identify these parameters.

MATERIALS AND METHODS

Eighteen patients with Moyamoya disease (5 men, 13 women; ages, 21-55 years) were retrospectively analyzed. CBF values of pulsed continuous arterial spin-labeling using 2 postlabeling delays (short arterial spin-labeling, 1525 ms; delayed arterial spin-labeling, 2525 ms) were compared with CBF values measured by ¹⁵O-gas PET. All plots were divided into 2 groups by the cutoff of time-based parameters (the time of the maximum observed concentration, TTP, MTT, delay of MTT to cerebellum, and disease severity [symptomatic or not]). The ratio of 2 arterial spin-labeling CBFs (delayed arterial spin-labeling CBF to short arterial spin-labeling CBF) was compared with time-based parameters: time of the maximum observed concentration, TTP, and MTT.

RESULTS

The short arterial spin-labeling-CBF values were significantly correlated with the PET-CBF values (r = 0.63; P = .01). However, the short arterial spin-labeling-CBF value dropped in the regions with severe perfusion delay. The delayed arterial spin-labeling CBF overestimated PET-CBF regardless of the degree of perfusion delay. Delayed arterial spin-labeling CBF/short arterial spin-labeling CBF was well correlated with the time of the maximum observed concentration, TTP, and MTT (ρ = 0.71, 0.64, and 0.47, respectively).

CONCLUSIONS

Arterial spin-labeling using 2 postlabeling delays may detect PET-measured true CBF and perfusion delay in patients with Moyamoya disease. Provided its theoretic basis and limitations are considered, noninvasive arterial spin-labeling could be a useful alternative for evaluating the hemodynamics of Moyamoya disease.

Performance of computed tomography angiography to determine anterograde and collateral blood flow status in patients with symptomatic middle cerebral artery stenosis

Background The purpose of this study was to determine the performance of computed tomography angiography (CTA) by using a scoring system to predict anterograde and collateral blood flow status in patients with symptomatic middle cerebral artery (MCA) stenosis with use of conventional angiography as standard reference. Methods We retrospectively identified all consecutive patients with unilateral symptomatic MCA stenosis in our center who underwent conventional angiography and CTA within 1 month. The anterograde and collateral blood flow (AnCo) scoring system consisted of anterograde score (AnS) and collateral score (CoS). Evaluation of the CTA images was done independently by two readers, based on the AnCo scoring system. The conventional angiography was assessed by using the Thrombolysis in Cerebral Infarction (TICI) and American Society of Interventional and Therapeutic Neuroradiology (ASITN/SIR) scoring system to determine the status of anterograde and collateral blood flow. Diagnostic performance of AnCo was evaluated by using the area under the receiver operating characteristic (ROC) curve. Results A total of 61 patients were included in the analysis with mean age of 53.4 ± 11.0 years. AnS demonstrated a strong correlation with TICI with statistical significance ( r = 0.786; p < 0.001). CoS had a modest yet statistically significant correlation with ASITN/SIR ( r = 0.574; p < 0.001). The ROC curve analysis for AnS demonstrated an area under the curve (AUC) of 0.894 ( p < 0.001) and the ROC curve analysis for CoS showed an AUC of 0.824 ( p < 0.001). Conclusions CTA was a potential method to evaluate anterograde and collateral blood flow status in patients with symptomatic unilateral MCA stenosis.

Expanding the concept of neuroprotection for acute ischemic stroke: The pivotal roles of reperfusion and the collateral circulation

This review surveys the efforts taken to achieve clinically efficacious protection of the ischemic brain and underscores the necessity of expanding our purview to include the essential role of cerebral perfusion and the collateral circulation. We consider the development of quantitative strategies to measure cerebral perfusion at the regional and local levels and the application of these methods to elucidate flow-related thresholds of ischemic viability and to characterize the ischemic penumbra. We stress that the modern concept of neuroprotection must consider perfusion, the necessary substrate upon which ischemic brain survival depends. We survey the major mechanistic approaches to neuroprotection and review clinical neuroprotection trials, focusing on those phase 3 multicenter clinical trials for acute ischemic stroke that have been completed or terminated. We review the evolution of thrombolytic therapies; consider the lessons learned from the initial, negative multicenter trials of endovascular therapy; and emphasize the highly successful positive trials that have finally established a clinical role for endovascular clot removal. As these studies point to the brain's collateral circulation as key to successful reperfusion, we next review the anatomy and pathophysiology of collateral perfusion as it relates to ischemic infarction, as well as the molecular and genetic influences on collateral development. We discuss the current MR and CT-based diagnostic methods for assessing the collateral circulation and the prognostic significance of collaterals in ischemic stroke, and we consider past and possible future therapeutic directions.

Arterial Spin-Labeling Magnetic Resonance Perfusion Imaging with Dual Postlabeling Delay in Internal Carotid Artery Steno-occlusion: Validation with Digital Subtraction Angiography

BACKGROUND

Arterial spin-labeling magnetic resonance perfusion imaging (ASL-MRI) allows noninvasive measurement of cerebral blood flow (CBF) but depends on the arterial transit time (ATT). With the commonly used single postlabeling delay (PLD) of 1.5 seconds, slow flow through collateral vessels may be underestimated. We used both 1.5 and 2.5 seconds to overcome this problem. We validated these PLD settings by measuring the ATT and identifying the angiographic circulation using digital subtraction angiography (DSA).

METHODS

We retrospectively selected 5 patients with unilateral occlusion or stenosis of the internal carotid artery (ICA) in whom ASL-MRI showed low CBF with 1.5-second PLD in the target area and improved CBF with 2.5-second PLD. We then compared the ASL-MRI findings visually with DSA findings at 1.5 and 2.5 seconds after injection of the contrast. When arterial transit artifacts (ATAs), attributed to stagnant intravascular spin-labeled blood, were observed, DSA findings were analyzed visually at 4.5 seconds.

RESULTS

DSA revealed that the hypovascular area seen at 1.5 seconds was improved via the primary and secondary collaterals and delayed anterograde flow at 2.5 seconds. Serpiginous or round-shaped ATAs, which appeared in nearly the same configuration on dual PLD ASL-MRI, were attributed to stagnant collaterals and flow in the M2 portion of the middle cerebral artery and ICA during the late venous phase.

CONCLUSIONS

Use of dual PLD times was validated by the DSA findings. ATA detection using the dual PLDs also differentiated well-developed and stagnant collateral vessels from focal hyperperfusion.