Arrival time correction for dynamic susceptibility contrast MR permeability imaging in stroke patients

Biomarkers of blood-brain barrier and neurovascular unit integrity in human cognitive impairment and dementia

Blood-brain barrier (BBB) dysfunction is recognized as an early step in the development of Alzheimer's disease and related dementias (ADRD). Biomarkers are needed to monitor BBB integrity over time, better understand the role of the BBB in neurodegeneration, potentially help define long-term ADRD risk, and monitor effects of therapeutics. In this review, we discuss the current biomarkers used to detect human BBB dysfunction in the context of cognitive decline and dementia. We also discuss promising candidate fluid biomarkers to detect BBB dysfunction in blood. HIGHLIGHTS: BBB permeability occurs during normal aging and is further exacerbated in ADRD. In this review, we discuss in vivo imaging and CSF biomarkers of BBB dysfunction currently used in the setting of aging and ADRD in humans. We also review promising candidate blood-based biomarkers that may represent BBB dysfunction.

Blood-brain barrier breakdown in brain ischemia: Insights from MRI perfusion imaging

Brain ischemia is a major cause of neurological dysfunction and mortality worldwide. It occurs not only acutely, such as in acute ischemic stroke (AIS), but also in chronic conditions like cerebral small vessel disease (cSVD). Any other conditions resulting in brain hypoperfusion can also lead to ischemia. Ischemic events can cause blood-brain barrier (BBB) disruption and, ultimately, white matter alterations, contributing to neurological deficits and long-term functional impairments. Hence, understanding the mechanisms of BBB breakdown and white matter injury across various ischemic conditions is critical for developing effective interventions and improving patient outcomes. This review discusses the proposed mechanisms of ischemia-related BBB breakdown. Moreover, magnetic resonance imaging (MRI) based perfusion-weighted imaging (PWI) techniques sensitive to BBB permeability changes are described, including dynamic contrast-enhanced (DCE-MRI) and dynamic susceptibility contrast MRI (DSC-MRI), two perfusion-weighted imaging (PWI). These PWI techniques provide valuable insights that improve our understanding of the complex early pathophysiology of brain ischemia, which can lead to better assessment and management. Finally, in this review, we explore the implications of the mentioned neuroimaging findings, which emphasize the potential of neuroimaging biomarkers to guide personalized treatment and inform novel neuroprotective strategies. This review highlights the importance of investigating BBB changes in brain ischemia and the critical role of advanced neuroimaging in improving patient care and advancing stroke research.

Cerebral collaterals are associated with pre-treatment brain-blood barrier permeability in acute ischemic stroke patients

INTRODUCTION

To investigate the relationship between collaterals and blood-brain barrier (BBB) permeability on pre-treatment MRI in a cohort of acute ischemic stroke (AIS) patients treated with thrombectomy.

METHODS

We conducted a retrospective analysis of the HIBISCUS-STROKE cohort, a single-center observational study that enrolled patients treated with thrombectomy from 2016 to 2022. Dynamic-susceptibility MRIs were post-processed to generate K2 maps with arrival-time correction, which were co-registered with apparent diffusion coefficient (ADC) maps. The 90th percentile of K2 was extracted from the infarct core-defined by an ADC ≤ 620 × 10-6 mm2/s with manual adjustments-and expressed as a percentage change compared to the contralateral white matter. Collaterals were assessed using pre-thrombectomy digital subtraction arteriography with an ASITN/SIR score < 3 defining poor collaterals.

RESULTS

Out of 249 enrolled, 101 (40.6%) were included (median age: 72.0 years, 52.5% of males, median NIHSS score at admission: 15.0). Patients with poor collaterals (n = 44) had worse NIHSS scores (median: 16.0 vs 13.0, p = 0.04), larger infarct core volumes (median: 43.7 mL vs 9.5 mL, p < 0.0001), and higher increases in K2 (median: 346.3% vs 152.7%, p = 0.003). They were less likely to achieve successful recanalization (21/44 vs 51/57, p < 0.0001) and experienced more frequent hemorrhagic transformation (16/44 vs 9/57, p = 0.03). On multiple variable analysis, poor collaterals were associated with larger infarct cores (odds ratio (OR) = 1.12, 95% confidence interval (CI): [1.07, 1.17], p < 0.0001) and higher increases in K2 (OR = 6.63, 95% CI: [2.19, 20.08], p = 0.001).

CONCLUSION

Poor collaterals are associated with larger infarct cores and increased BBB permeability at admission MRI.

CLINICAL RELEVANCE STATEMENT

Poor collaterals are associated with a larger infarct core and increased BBB permeability at admission MRI of AIS patients treated with thrombectomy. These findings may have translational interests for extending thrombolytic treatment eligibility and developing neuroprotective strategies.

KEY POINTS

In AIS, collaterals and BBB disruption have been both linked to hemorrhagic transformation. Poor collaterals were associated with larger ischemic cores and increased BBB permeability on pre-treatment MRI. These findings could contribute to hemorrhagic transformation risk stratification, thereby refining clinical decision-making for reperfusion therapies.

Blood-brain barrier profile pretreatment is associated with hemorrhagic transformation after endovascular reperfusion

BACKGROUND

While advances in endovascular thrombectomy (EVT) have led to high reperfusion rates, most patients treated with EVT do not avoid disability. Post-reperfusion hemorrhagic transformation (HT) is a potential target for improving outcomes. This study examined pretreatment blood-brain barrier (BBB) disruption in tissue that would subsequently become part of the final infarct to evaluate its role in post-EVT HT.

METHODS

This post hoc analysis of the FRAME study, which enrolled patients with anterior large vessel occlusion who received EVT within 6 hours of onset, included patients if they had successful pretreatment MRI perfusion weighted imaging (PWI) and underwent successful EVT. BBB disruption was measured as the percent signal change due to gadolinium leakage on the PWI source images prior to thrombectomy. Mean permeability derangement (MPD) was defined as the average of all voxels in the stroke core that are two standard deviations above normal. The primary outcome was hemorrhagic transformation with parenchymal hematoma (PH).

RESULTS

In total, 164 patients were included; mean age was 71 and 48% were female. PH occurred in 57 patients. Median MPD was 13.5% for patients with PH versus 3.6% for patients without (p < 0.0001). Elevated MPD was independently associated with PH with a 20% increased risk of PH for each 5% increase in MPD (OR 1.206; 95% CI 1.037:1.405; p = 0.0147, adjusted for NIHSS and procedure duration).

CONCLUSIONS

Even in patients who are successfully recanalized in an early time window, pretreatment BBB disruption in regions that go on to infarct is associated with an increased risk of post-EVT HT.

Blood-brain barrier disruption and increased free water are associated with worse cognitive performance in patients with chronic cerebrovascular disease

Progression of cerebral small vessel disease (CSVD) is associated with cognitive decline. Blood-brain barrier disruption (BBBD) and fluid extravasation to the interstitial space may contribute to progression of white matter hyperintensities (WMH). We hypothesized that increased free water (FW) would colocalize with BBBD and relate to cognitive performance. Patients with ischemic stroke/TIA at least 3 months prior with at least early confluent WMH were studied cross-sectionally with the Montreal Cognitive Assessment (MoCA), diffusion tensor imaging, and dynamic susceptibility contrast imaging. White matter (WM) was segmented into WMH, WMH penumbra, and normal appearing white matter (NAWM). Colocalization of elevated FW and BBBD and their associations with MoCA performance were evaluated. 58 patients were included (mean age 69, 36 % female). Higher BBBD colocalized with elevated FW. Elevated FW in all white matter, NAWM, WMH penumbra, and WMH lesions was associated with lower MoCA score. Increased BBBD in all WM, NAWM, and WMH penumbra was associated with lower MoCA. In WMH penumbra, both elevated FW and increased BBBD were independently associated with lower MoCA. We found agreement between 2 different biomarkers implicated in the pathogenesis of CSVD that independently demonstrated association with cognitive performance when measured in the area of postulated disease activity.

Simultaneous perfusion, diffusion, T2 *, and T1 mapping with MR fingerprinting

PURPOSE

Quantitative mapping of brain perfusion, diffusion, T2 *, and T1 has important applications in cerebrovascular diseases. At present, these sequences are performed separately. This study aims to develop a novel MRI technique to simultaneously estimate these parameters.

METHODS

This sequence to measure perfusion, diffusion, T2 *, and T1 mapping with magnetic resonance fingerprinting (MRF) was based on a previously reported MRF-arterial spin labeling (ASL) sequence, but the acquisition module was modified to include different TEs and presence/absence of bipolar diffusion-weighting gradients. We compared parameters derived from the proposed method to those derived from reference methods (i.e., separate sequences of MRF-ASL, conventional spin-echo DWI, and T2 * mapping). Test-retest repeatability and initial clinical application in two patients with stroke were evaluated.

RESULTS

The scan time of our proposed method was 24% shorter than the sum of the reference methods. Parametric maps obtained from the proposed method revealed excellent image quality. Their quantitative values were strongly correlated with those from reference methods and were generally in agreement with values reported in the literature. Repeatability assessment revealed that ADC, T2 *, T1 , and B1 + estimation was highly reliable, with voxelwise coefficient of variation (CoV) <5%. The CoV for arterial transit time and cerebral blood flow was 16% ± 3% and 25% ± 9%, respectively. The results from the two patients with stroke demonstrated that parametric maps derived from the proposed method can detect both ischemic and hemorrhagic stroke.

CONCLUSION

The proposed method is a promising technique for multi-parametric mapping and has potential use in patients with stroke.

Dynamic Susceptibility Contrast Perfusion, Part 2: Deployment With and Without Contrast Leakage Present

A thorough description of perfusion analysis and basic DSC MR acquisition concepts has been described in the companion article to this article, which the interested reader may also find useful. DSC MR imaging requires an MR imaging pulse sequence that is sensitive to magnetic susceptibility changes to register the contrast concentration changes when GBCA passes through the capillary bed. Any pulse sequence that has T2∗-weighting can be used to pick up these changes, provided that the sequence is fast enough to acquire an image of that slice of tissue at least every 1 to 2 second.

Blood-Brain Barrier Permeability and Kinetics of Inflammatory Markers in Acute Stroke Patients Treated With Thrombectomy

BACKGROUND AND OBJECTIVES

The aim of this study was to investigate the relationship between baseline blood-brain barrier (BBB) permeability and the kinetics of circulating inflammatory markers in a cohort of acute ischemic stroke (AIS) patients treated with mechanical thrombectomy.

METHODS

The CoHort of Patients to Identify Biological and Imaging markerS of CardiovascUlar Outcomes in Stroke includes AIS patients treated with mechanical thrombectomy after admission MRI and undergoing a sequential assessment of circulating inflammatory markers. Baseline dynamic susceptibility perfusion MRI was postprocessed with arrival time correction to provide K2 maps reflecting BBB permeability. After coregistration of apparent diffusion coefficient and K2 maps, the 90th percentile of K2 value was extracted within baseline ischemic core and expressed as a percentage change compared with contralateral normal-appearing white matter. Population was dichotomized according to the median K2 value. Univariable and multiple variable logistic regression analyses were performed to investigate factors associated with increased pretreatment BBB permeability in the whole population and in patients with symptom onset <6 hours.

RESULTS

In the whole population (n = 105 patients, median K2 = 1.59), patients with an increased BBB permeability had higher serum levels of matrix metalloproteinase (MMP)-9 at H48 (p = 0.02), a higher C-reactive protein (CRP) serum level at H48 (p = 0.01), poorer collateral status (p = 0.01), and a larger baseline ischemic core (p < 0.001). They were more likely to have hemorrhagic transformation (p = 0.008), larger final lesion volume (p = 0.02), and worst neurologic outcome at 3 months (p = 0.04). The multiple variable logistic regression indicated that an increased BBB permeability was associated only with ischemic core volume (odds ratio [OR] 1.04, 95% CI 1.01-1.06, p < 0.0001). Restricting analysis to patients with symptom onset <6 hours (n = 72, median K2 = 1.27), participants with an increased BBB permeability had higher serum levels of MMP-9 at H0 (p = 0.005), H6 (p = 0.004), H24 (p = 0.02), and H48 (p = 0.01), higher CRP levels at H48 (p = 0.02), and a larger baseline ischemic core (p < 0.0001). The multiple variable logistic analysis showed that increased BBB permeability was independently associated with higher H0 MMP-9 levels (OR 1.33, 95% CI 1.12-1.65, p = 0.01) and a larger ischemic core (OR 1.27, 95% CI 1.08-1.59, p = 0.04).

DISCUSSION

In AIS patients, increased BBB permeability is associated with a larger ischemic core. In the subgroup of patients with symptom onset <6 hours, increased BBB permeability is independently associated with higher H0 MMP-9 levels and a larger ischemic core.

Vascular contributions to Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia and is characterized by progressive neurodegeneration and cognitive decline. Understanding the pathophysiology underlying AD is paramount for the management of individuals at risk of and suffering from AD. The vascular hypothesis stipulates a relationship between cardiovascular disease and AD-related changes although the nature of this relationship remains unknown. In this review, we discuss several potential pathological pathways of vascular involvement in AD that have been described including dysregulation of neurovascular coupling, disruption of the blood brain barrier, and reduced clearance of metabolite waste such as beta-amyloid, a toxic peptide considered the hallmark of AD. We will also discuss the two-hit hypothesis which proposes a 2-step positive feedback loop in which microvascular insults precede the accumulation of Aß and are thought to be at the origin of the disease development. At neuroimaging, signs of vascular dysfunction such as chronic cerebral hypoperfusion have been demonstrated, appearing early in AD, even before cognitive decline and alteration of traditional biomarkers. Cerebral small vessel disease such as cerebral amyloid angiopathy, characterized by the aggregation of Aß in the vessel wall, is highly prevalent in vascular dementia and AD patients. Current data is unclear whether cardiovascular disease causes, precipitates, amplifies, precedes, or simply coincides with AD. Targeted imaging tools to quantitatively evaluate the intracranial vasculature and longitudinal studies in individuals at risk for or in the early stages of the AD continuum could be critical in disentangling this complex relationship between vascular disease and AD.

Abnormal cerebral hemodynamics and blood-brain barrier permeability detected with perfusion MRI in systemic lupus erythematosus patients

OBJECTIVE

Dynamic susceptibility contrast (DSC) magnetic resonance imaging (MRI) has previously shown alterations in cerebral perfusion in patients with systemic lupus erythematosus (SLE). However, the results have been inconsistent, in particular regarding neuropsychiatric (NP) SLE. Thus, we investigated perfusion-based measures in different brain regions in SLE patients with and without NP involvement, and additionally, in white matter hyperintensities (WMHs), the most common MRI pathology in SLE patients.

MATERIALS AND METHODS

We included 3 T MRI images (conventional and DSC) from 64 female SLE patients and 19 healthy controls (HC). Three different NPSLE attribution models were used: the Systemic Lupus International Collaborating Clinics (SLICC) A model (13 patients), the SLICC B model (19 patients), and the American College of Rheumatology (ACR) case definitions for NPSLE (38 patients). Normalized cerebral blood flow (CBF), cerebral blood volume (CBV) and mean transit time (MTT) were calculated in 26 manually drawn regions of interest and compared between SLE patients and HC, and between NPSLE and non-NPSLE patients. Additionally, normalized CBF, CBV and MTT, as well as absolute values of the blood-brain barrier leakage parameter (K2) were investigated in WMHs compared to normal appearing white matter (NAWM) in the SLE patients.

RESULTS

After correction for multiple comparisons, the most prevalent finding was a bilateral significant decrease in MTT in SLE patients compared to HC in the hypothalamus, putamen, right posterior thalamus and right anterior insula. Significant decreases in SLE compared to HC were also found for CBF in the pons, and for CBV in the bilateral putamen and posterior thalamus. Significant increases were found for CBF in the posterior corpus callosum and for CBV in the anterior corpus callosum. Similar patterns were found for both NPSLE and non-NPSLE patients for all attributional models compared to HC. However, no significant perfusion differences were revealed between NPSLE and non-NPSLE patients regardless of attribution model. The WMHs in SLE patients showed a significant increase in all perfusion-based metrics (CBF, CBV, MTT and K2) compared to NAWM.

CONCLUSION

Our study revealed perfusion differences in several brain regions in SLE patients compared to HC, independently of NP involvement. Furthermore, increased K2 in WMHs compared to NAWM may indicate blood-brain barrier dysfunction in SLE patients. We conclude that our results show a robust cerebral perfusion, independent from the different NP attribution models, and provide insight into potential BBB dysfunction and altered vascular properties of WMHs in female SLE patients. Despite SLE being most prevalent in females, a generalization of our conclusions should be avoided, and future studies including all sexes are needed.

Microvascular Dysfunction in Blood-Brain Barrier Disruption and Hypoperfusion Within the Infarct Posttreatment Are Associated With Cerebral Edema

BACKGROUND

Factors contributing to cerebral edema in the post-hyperacute period of ischemic stroke (first 24-72 hours) are poorly understood. Blood-brain barrier (BBB) disruption and postischemic hyperperfusion reflect microvascular dysfunction and are associated with hemorrhagic transformation. We investigated the relationships between BBB integrity, cerebral blood flow, and space-occupying cerebral edema in patients who received acute reperfusion therapy.

METHODS

We performed a pooled analysis of patients treated for anterior circulation large vessel occlusion in the EXTEND-IA TNK and EXTEND-IA TNK part 2 trials who had MRI with dynamic susceptibility contrast-enhanced perfusion-weighted imaging 24 hours after treatment. We investigated the associations between BBB disruption and cerebral blood flow within the infarct with cerebral edema assessed using 2 metrics: first midline shift (MLS) trichotomized as an ordinal scale of negligible (<1 mm), mild (≥1 to <5 mm), or severe (≥5 mm), and second relative hemispheric volume (rHV), defined as the ratio of the 3-dimensional volume of the ischemic hemisphere relative to the contralateral hemisphere.

RESULTS

Of 238 patients analyzed, 133 (55.9%) had negligible, 93 (39.1%) mild, and 12 (5.0%) severe MLS at 24 hours. The associated median rHV was 1.01 (IQR, 1.00-1.028), 1.03 (IQR, 1.01-1.077), and 1.15 (IQR, 1.08-1.22), respectively. MLS and rHV were associated with poor functional outcome at 90 days (P<0.002). Increased BBB permeability was independently associated with more edema after adjusting for age, occlusion location, reperfusion, parenchymal hematoma, and thrombolytic agent used (MLS cOR, 1.12 [95% CI, 1.03-1.20], P=0.005; rHV β, 0.39 [95% CI, 0.24-0.55], P<0.0001), as was reduced cerebral blood flow (MLS cOR, 0.25 [95% CI, 0.10-0.58], P=0.001; rHV β, -2.95 [95% CI, -4.61 to -11.29], P=0.0006). In subgroup analysis of patients with successful reperfusion (extended Treatment in Cerebral Ischemia 2b-3, n=200), reduced cerebral blood flow remained significantly associated with edema (MLS cOR, 0.37 [95% CI, 0.14-0.98], P=0.045; rHV β, -2.59 [95% CI, -4.32 to -0.86], P=0.004).

CONCLUSIONS

BBB disruption and persistent hypoperfusion in the infarct after reperfusion treatment is associated with space-occupying cerebral edema. Further studies evaluating microvascular dysfunction during the post-hyperacute period as biomarkers of poststroke edema and potential therapeutic targets are warranted.

Seizures and epilepsy in patients with ischaemic stroke

BACKGROUND

With the increased efficacy of stroke treatments, diagnosis and specific treatment needs of patients with post-stroke seizures (PSS) and post-stroke epilepsy have become increasingly important. PSS can complicate the diagnosis of a stroke and the treatment of stroke patients, and can worsen post-stroke morbidity. This narrative review considers current treatment guidelines, the specifics of antiseizure treatment in stroke patients as well as the state-of-the-art in clinical and imaging research of post-stroke epilepsy. Treatment of PSS needs to consider indications for antiseizure medication treatment as well as individual clinical and social factors. Furthermore, potential interactions between stroke and antiseizure treatments must be carefully considered. The relationship between acute recanalizing stroke therapy (intravenous thrombolysis and mechanical thrombectomy) and the emergence of PSS is currently the subject of an intensive discussion. In the subacute and chronic post-stroke phases, important specific interactions between necessary antiseizure and stroke treatments (anticoagulation, cardiac medication) need to be considered. Among all forms of prevention, primary prevention is currently the most intensively researched. This includes specifically the repurposing of drugs that were not originally developed for antiseizure properties, such as statins. PSS are presently the subject of extensive basic clinical research. Of specific interest are the role of post-stroke excitotoxicity and blood-brain barrier disruption for the emergence of PSS in the acute symptomatic as well as late (> 1 week after the stroke) periods. Current magnetic resonance imaging research focussing on glutamate excitotoxicity as well as diffusion-based estimation of blood-brain barrier integrity aim to elucidate the pathophysiology of seizures after stroke and the principles of epileptogenesis in structural epilepsy in general. These approaches may also reveal new imaging-based biomarkers for prediction of PSS and post-stroke epilepsy.

CONCLUSION

PSS require the performance of individual risk assessments, accounting for the potential effectiveness and side effects of antiseizure therapy. The use of intravenous thrombolysis and mechanical thrombectomy is not associated with an increased risk of PSS. Advances in stroke imaging may reveal biomarkers for PSS.

Model-free leakage index estimation of the blood-brain barrier using dual dynamic susceptibility contrast MRI acquisition

Pharmacokinetic K2 mapping from dynamic susceptibility contrast (DSC)-MRI can be a sensitive technique for evaluating the vascular permeability of the subtly damaged blood-brain barrier (BBB) in ischemic regions. However, the K2 values of ischemic lesions depend upon the selection of the intact BBB reference region. As previous observations suggest that the ΔR2* curve of pre-loaded DSC-MRI is not significantly affected by the extravasation of contrast agent, dual DSC-MRI acquisitions can be performed to derive the BBB leakage index from the voxel-wise reference input function for ischemic regions. This study aims to demonstrate the robustness of such model-free leakage index estimation in ischemic brains. By configuring the relationship between dual ΔR2* curves of the intact contralateral brain, the deviation of the measured ΔR2* curve from the unloaded DSC-MRI with respect to the non-deviated ΔR2* curve in the pre-loaded DSC-MRI can be quantified as the BBB leakage index. Such model-free leakage index values from rats with transient middle carotid artery occlusion (tMCAO) (n = 17) and normal controls (n = 3) were evaluated and compared with conventional K2 values with multiple reference regions. Inter-subject leakage index values were also compared with the corresponding ΔT1 map. Evans-blue-stained images were used to validate the leakage index. For the tMCAO group, leakage index values correlated well with ΔT1 (Pearson's r = 0.828). The hyperintense area on the leakage index map matched well with the corresponding Evans-blue-stained area (Dice correlation = 0.626). The slopes of the scatter-plot from the leakage index (0.97-1.00) were observed to be more robust against changes in the reference region than those from conventional K2 values (0.94-1.07). In a subtly damaged BBB tMCAO model, model-free evaluation of vascular permeability using dual DSC-MRIs would provide a consistent measure of inter-subject vascular permeability.

MTT and Blood-Brain Barrier Disruption within Asymptomatic Vascular WM Lesions

BACKGROUND AND PURPOSE

White matter lesions of presumed ischemic origin are associated with progressive cognitive impairment and impaired BBB function. Studying the longitudinal effects of white matter lesion biomarkers that measure changes in perfusion and BBB patency within white matter lesions is required for long-term studies of lesion progression. We studied perfusion and BBB disruption within white matter lesions in asymptomatic subjects.

MATERIALS AND METHODS

Anatomic imaging was followed by consecutive dynamic contrast-enhanced and DSC imaging. White matter lesions in 21 asymptomatic individuals were determined using a Subject-Specific Sparse Dictionary Learning algorithm with manual correction. Perfusion-related parameters including CBF, MTT, the BBB leakage parameter, and volume transfer constant were determined.

RESULTS

MTT was significantly prolonged (7.88 [SD, 1.03] seconds) within white matter lesions compared with normal-appearing white (7.29 [SD, 1.14] seconds) and gray matter (6.67 [SD, 1.35] seconds). The volume transfer constant, measured by dynamic contrast-enhanced imaging, was significantly elevated (0.013 [SD, 0.017] minutes-1) in white matter lesions compared with normal-appearing white matter (0.007 [SD, 0.011] minutes-1). BBB disruption within white matter lesions was detected relative to normal white and gray matter using the DSC-BBB leakage parameter method so that increasing BBB disruption correlated with increasing white matter lesion volume (Spearman correlation coefficient = 0.44; P < .046).

CONCLUSIONS

A dual-contrast-injection MR imaging protocol combined with a 3D automated segmentation analysis pipeline was used to assess BBB disruption in white matter lesions on the basis of quantitative perfusion measures including the volume transfer constant (dynamic contrast-enhanced imaging), the BBB leakage parameter (DSC), and MTT (DSC). This protocol was able to detect early pathologic changes in otherwise healthy individuals.

Post-stroke blood-brain barrier disruption predicts poor outcome in patients enrolled in the ACTION study

BACKGROUND AND PURPOSE

A prior study found a link between post-stroke blood-brain barrier disruption and functional outcomes. The current study aimed to replicate this finding in a cohort of patients recruited in the context of a randomized clinical trial.

METHODS

The ACTION trial was a study of natalizumab in acute stroke patients. Patients with MRI-perfusion weighted imaging (PWI) were included in this post-hoc analysis. Blood-brain permeability images (BBPI) were calculated from the PWI source images. Mean BBPI values from the 24 h time point were compared with modified Rankin scores (mRS) at 5, 30, and 90-day assessments using linear regression. Good functional outcome (mRS< = 1) was compared with mean BBPI using logistic regression.

RESULTS

One hundred and nineteen patients were included in the analysis (median age = 74, 43% female). Higher mean BBPI was associated with worse mRS at 5 days (p = 0.002; r² = 0.078) and 30 days (p = 0.036; r² = 0.039) but did not reach statistical significance at 90 days (p = 0.30; r² = 0.010). When removing high-value outliers, all outcome measures showed a stronger relationship with mean BBPI. Logistic regression found that with every 1% increase in mean BBPI measured 24 h after the stroke, the likelihood of achieving a good functional outcome at 90 days is decreased by half (OR = 0.53; CI = 0.30:0.95; p = 0.032).

CONCLUSIONS

With sufficient image quality, elevated BBPI measured in the days after an ischemic event is predictive of worse functional outcome and may serve as a biomarker for post-stroke inflammation.

Effect of Applying Leakage Correction on rCBV Measurement Derived From DSC-MRI in Enhancing and Nonenhancing Glioma

Purpose

Relative cerebral blood volume (rCBV) is the most widely used parameter derived from DSC perfusion MR imaging for predicting brain tumor aggressiveness. However, accurate rCBV estimation is challenging in enhancing glioma, because of contrast agent extravasation through a disrupted blood-brain barrier (BBB), and even for nonenhancing glioma with an intact BBB, due to an elevated steady-state contrast agent concentration in the vasculature after first passage. In this study a thorough investigation of the effects of two different leakage correction algorithms on rCBV estimation for enhancing and nonenhancing tumors was conducted.

Methods

Two datasets were used retrospectively in this study: 1. A publicly available TCIA dataset (49 patients with 35 enhancing and 14 nonenhancing glioma); 2. A dataset acquired clinically at Erasmus MC (EMC, Rotterdam, NL) (47 patients with 20 enhancing and 27 nonenhancing glial brain lesions). The leakage correction algorithms investigated in this study were: a unidirectional model-based algorithm with flux of contrast agent from the intra- to the extravascular extracellular space (EES); and a bidirectional model-based algorithm additionally including flow from EES to the intravascular space.

Results

In enhancing glioma, the estimated average contrast-enhanced tumor rCBV significantly (Bonferroni corrected Wilcoxon Signed Rank Test, p < 0.05) decreased across the patients when applying unidirectional and bidirectional correction: 4.00 ± 2.11 (uncorrected), 3.19 ± 1.65 (unidirectional), and 2.91 ± 1.55 (bidirectional) in TCIA dataset and 2.51 ± 1.3 (uncorrected), 1.72 ± 0.84 (unidirectional), and 1.59 ± 0.9 (bidirectional) in EMC dataset. In nonenhancing glioma, a significant but smaller difference in observed rCBV was found after application of both correction methods used in this study: 1.42 ± 0.60 (uncorrected), 1.28 ± 0.46 (unidirectional), and 1.24 ± 0.37 (bidirectional) in TCIA dataset and 0.91 ± 0.49 (uncorrected), 0.77 ± 0.37 (unidirectional), and 0.67 ± 0.34 (bidirectional) in EMC dataset.

Conclusion

Both leakage correction algorithms were found to change rCBV estimation with BBB disruption in enhancing glioma, and to a lesser degree in nonenhancing glioma. Stronger effects were found for bidirectional leakage correction than for unidirectional leakage correction.

The Relationship Between Penumbral Tissue and Blood-Brain Barrier Disruption in Acute Stroke Patients Presenting in an Extended Time Window

Background: Penumbral brain tissue identified with multimodal imaging can be salvaged with reperfusion in an extended time window. The risk of severe hemorrhagic complications after reperfusion therapy increases with worsening disruption of the blood-brain barrier (BBB). The relationship between penumbral tissue and BBB disruption has not been previously studied. Methods: Stroke patients presenting in an extended time window without a large vessel occlusion who underwent diffusion-perfusion MRI within 24 h of last-seen-normal were included. The volume of penumbral tissue was calculated using mismatch on MRI. Mean permeability derangement (MPD) of the BBB was measured within the ischemic lesion. A target profile (TP) for treatment was defined based on the EXTEND trial. Results: 222 patients were included with a median age of 73 and 55% women. The median NIHSS was 6, the mean core volume was 14 ml, the mean ischemic volume was 47 mL and the mean mismatch volume was 33 mL. Higher MPD was significantly associated with less mismatch volume (p = 0.001). A target profile was associated with lower MPD (OR 0.97; CI 0.96:0.99; p < 0.001). Of the 105 patients who had a TP, 31 (30%) had a MPD > 20% suggesting an increased risk of hemorrhage. Thus, 33% (74/222) of patients had a favorable profile for benefit and safety. Conclusions: Patients presenting in an extended time window with a favorable penumbral profile for treatment have less severe BBB disruption. Up to a third of patients who currently go untreated could be considered for enrollment in a clinical trial of thrombolysis in an extended time window.

Pathophysiology of Blood-Brain Barrier Permeability Throughout the Different Stages of Ischemic Stroke and Its Implication on Hemorrhagic Transformation and Recovery

The blood-brain barrier (BBB) is a dynamic interface responsible for maintaining the central nervous system homeostasis. Its unique characteristics allow protecting the brain from unwanted compounds, but its impairment is involved in a vast number of pathological conditions. Disruption of the BBB and increase in its permeability are key in the development of several neurological diseases and have been extensively studied in stroke. Ischemic stroke is the most prevalent type of stroke and is characterized by a myriad of pathological events triggered by an arterial occlusion that can eventually lead to fatal outcomes such as hemorrhagic transformation (HT). BBB permeability seems to follow a multiphasic pattern throughout the different stroke stages that have been associated with distinct biological substrates. In the hyperacute stage, sudden hypoxia damages the BBB, leading to cytotoxic edema and increased permeability; in the acute stage, the neuroinflammatory response aggravates the BBB injury, leading to higher permeability and a consequent risk of HT that can be motivated by reperfusion therapy; in the subacute stage (1-3 weeks), repair mechanisms take place, especially neoangiogenesis. Immature vessels show leaky BBB, but this permeability has been associated with improved clinical recovery. In the chronic stage (>6 weeks), an increase of BBB restoration factors leads the barrier to start decreasing its permeability. Nonetheless, permeability will persist to some degree several weeks after injury. Understanding the mechanisms behind BBB dysregulation and HT pathophysiology could potentially help guide acute stroke care decisions and the development of new therapeutic targets; however, effective translation into clinical practice is still lacking. In this review, we will address the different pathological and physiological repair mechanisms involved in BBB permeability through the different stages of ischemic stroke and their role in the development of HT and stroke recovery.

A Comprehensive View on MRI Techniques for Imaging Blood-Brain Barrier Integrity

The blood-brain barrier (BBB) is the interface between the blood and brain tissue, which regulates the maintenance of homeostasis within the brain. Impaired BBB integrity is increasingly associated with various neurological diseases. To gain a better understanding of the underlying processes involved in BBB breakdown, magnetic resonance imaging (MRI) techniques are highly suitable for noninvasive BBB assessment. Commonly used MRI techniques to assess BBB integrity are dynamic contrast-enhanced and dynamic susceptibility contrast MRI, both relying on leakage of gadolinium-based contrast agents. A number of conceptually different methods exist that target other aspects of the BBB. These alternative techniques make use of endogenous markers, such as water and glucose, as contrast media. A comprehensive overview of currently available MRI techniques to assess the BBB condition is provided from a scientific point of view, including potential applications in disease. Improvements that are required to make these techniques clinically more easily applicable will also be discussed.

Pattern recognition analysis of dynamic susceptibility contrast (DSC)‐MRI curves automatically segments tissue areas with intact blood–brain barrier in a rat stroke model: A feasibility and comparison study

Background

The manual segmentation of intact blood–brain barrier (BBB) regions in the stroke brain is cumbersome, due to the coexistence of infarction, large blood vessels, ventricles, and intact BBB regions, specifically in areas with weak signal enhancement following contrast agent injection.

Hypothesis

That from dynamic susceptibility contrast (DSC)‐MRI alone, without user intervention, regions of weak BBB damage can be segmented based on the leakage‐related parameter K 2 and the extent of intact BBB regions, needed to estimate K 2 values, determined.

Study Type

Feasibility.

Animal Model

Ten female Sprague–Dawley rats (SD, 200–250g) underwent 1‐hour middle carotid artery occlusion (MCAO) and 1‐day reperfusion. Two SD rats underwent 1‐hour MCAO with 3‐day and 5‐day reperfusion.

Field Strength/Sequence

7T; ADC and T1 maps using diffusion‐weighted echo planar imaging (EPI) and relaxation enhancement (RARE) with variable repetition time (TR), respectively. dynamic contrast‐enhanced (DCE)‐MRI using FLASH. DSC‐MRI using gradient‐echo EPI.

Assessment

Constrained nonnegative matrix factorization (cNMF) was applied to the dynamic ‐curves of DSC‐MRI (<4 min) in a BBB‐disrupted rat model. Areas of voxels with intact BBB, classified by automated cNMF analyses, were then used in estimating K 1 and K 2 values, and compared with corresponding values from manually‐derived areas.

Statistical Tests

Mean ± standard deviation of ΔT1‐differences between ischemic and healthy areas were displayed with unpaired Student's t‐tests. Scatterplots were displayed with slopes and intercepts and Pearson's r values were evaluated between K 2 maps obtained with automatic (cNMF)‐ and manually‐derived regions of interest (ROIs) of the intact BBB region.

Results

Mildly BBB‐damaged areas (indistinguishable from DCE‐MRI (10 min) parameters) were automatically segmented. Areas of voxels with intact BBB, classified by automated cNMF, matched closely the corresponding, manually‐derived areas when respective areas were used in estimating K 2 maps (Pearson's r = 0.97, 12 slices).

Data Conclusion

Automatic segmentation of short DSC‐MRI data alone successfully identified areas with intact and compromised BBB in the stroke brain and compared favorably with manual segmentation.

Level of Evidence: 3

Technical Efficacy: Stage 1

J. Magn. Reson. Imaging 2020;51:1369–1381.

Blood-brain barrier integrity of stroke patients presenting in an extended time window

Background

Current guidelines limit thrombolytic treatment of stroke to those patients who present within 4.5 h to minimize the risk of hemorrhagic complications. Risk of hemorrhage increases with increasing blood-brain barrier (BBB) disruption. This study aimed to determine, in a cohort of patients presenting outside of an IV-tPA treatment window, whether disruption of the BBB is time dependent, and what proportion of patients could be safely treated.

Methods

We analyzed untreated stroke patients, seen between 2011 and 2015, who had MRI studies in the time window of 4 to 24 h from symptoms onset. Permeability of the BBB was measured within the ischemic tissue using an application of dynamic susceptibility contrast imaging. Patients were dichotomized into two groups based on a 20% threshold of BBB disruption and compared using logistic regression.

Results

Of the 222 patients included in the final analysis, over half, 129 (58%), had preserved BBB integrity below the 20% threshold. There was no relationship between time imaged after symptom onset and the amount of BBB disruption (p = 0.138) across the population; BBB disruption varied widely.

Conclusions

Estimating BBB integrity may help to expand the treatment window for stroke patients by identifying those individuals for whom thrombolytic therapy can be considered.

Post-Stroke Blood-Brain Barrier Disruption and Poor Functional Outcome in Patients Receiving Thrombolytic Therapy

BACKGROUND AND PURPOSE

The role played by post-stroke inflammation after an ischemic event in limiting functional recovery remains unclear. One component of post-stroke inflammation is disruption of the blood-brain barrier (BBB). This study examines the relationship between post-stroke BBB disruption and functional outcome.

METHODS

Acute stroke patients treated with thrombolysis underwent magnetic resonance imaging scanning 24 h and 5 days after their initial event. BBB permeability maps were generated from perfusion weighted imaging. Average permeability was calculated in the affected hemisphere. Good functional outcome, defined as a modified Rankin score of 0 or 1, was compared with average permeability using logistic regression.

RESULTS

Of the 131 patients enrolled, 76 patients had the necessary data to perform the analysis at 24 h, and 58 -patients had data for the 5-day assessment. Higher BBB permeability measured at 24 h (OR 0.57; 95% CI 0.33-0.99, p = 0.045) and at 5 days (OR 0.24; 95% CI 0.09-0.66, p = 0.005) was associated with worse functional outcome 1-3 months after the acute ischemic stroke. For every percentage increase in BBB disruption at 5 days, there was a 76% decrease in the chance of achieving a good functional outcome after stroke. Multivariate analysis found this to be independent of age, stroke volume, or clinical stroke severity.

CONCLUSIONS

Post-stroke BBB disruption appears to be predictive of functional outcome irrespective of stroke size.

Sustained Opening of the Blood-Brain Barrier with Progressive Accumulation of White Matter Hyperintensities Following Ischemic Stroke

Objective: To report a patient in whom an acute ischemic stroke precipitated chronic blood-brain barrier (BBB) disruption and expansion of vascular white matter hyperintensities (WMH) into regions of normal appearing white matter (NAWM) during the following year. Background: WMH are a common finding in patients with vascular risk factors such as a history of stroke. The pathophysiology of WMH is not fully understood; however, there is growing evidence to suggest that the development of WMH may be preceded by the BBB disruption in the NAWM. Methods: We studied a patient enrolled in the National Institutes of Health Natural History of Stroke Study who was scanned with magnetic resonance imaging (MRI) after presenting to the emergency room with an acute stroke. After a treatment with IV tPA, she underwent further MRI scanning at 2 h, 24 h, 5 days, 30 days, 90 days, 6 months, and 1-year post stroke. BBB permeability images were generated from the perfusion weighted imaging (PWI) source images. MRIs from each time point were co-registered to track changes in BBB disruption and WMH over time. Results: An 84-year-old woman presented after acute onset right hemiparesis, right-sided numbness and aphasia with an initial NIHSS of 13. MRI showed diffusion restriction in the left frontal lobe and decreased blood flow on perfusion imaging. Fluid attenuated inversion recovery (FLAIR) imaging showed bilateral confluent WMH involving the deep white matter and periventricular regions. She was treated with IV tPA without complication and her NIHSS improved initially to 3 and ultimately to 0. Permeability maps identified multiple regions of chronic BBB disruption remote from the acute stroke, predominantly spanning the junction of WMH and NAWM. The severity of BBB disruption was greatest at 24 h after the stroke but persisted on subsequent MRI scans. Progression of WMH into NAWM over the year of observation was detected bilaterally but was most dramatic in the regions adjacent to the initial stroke. Conclusions: WMH-associated BBB disruption may be exacerbated by an acute stroke, even in the contralateral hemisphere, and can persist for months after the initial event. Transformation of NAWM to WMH may be evident in areas of BBB disruption within a year after the stroke. Further studies are needed to investigate the relationship between chronic BBB disruption and progressive WMH in patients with a history of cerebrovascular disease and the potential for acute stroke to trigger or exacerbate the process leading to the development of WMH.

A comparison of pseudo-continuous arterial spin labelling and dynamic susceptibility contrast MRI with and without contrast agent leakage correction in paediatric brain tumours

OBJECTIVE:

To investigate correlations between MRI perfusion metrics measured by dynamic susceptibility contrast and arterial spin labelling in paediatric brain tumours.

METHODS:

15 paediatric patients with brain tumours were scanned prospectively using pseudo-continuous arterial spin labelling (ASL) and dynamic susceptibility contrast (DSC-) MRI with a pre-bolus to minimise contrast agent leakage. Cerebral blood flow (CBF) maps were produced using ASL. Cerebral blood volume (CBV) maps with and without contrast agent leakage correction using the Boxerman technique and the leakage parameter, K₂, were produced from the DSC data. Correlations between the metrics produced were investigated.

RESULTS:

Histology resulted in the following diagnoses: pilocytic astrocytoma (n = 7), glioblastoma (n = 1), medulloblastoma (n = 1), rosette-forming glioneuronal tumour of fourth ventricle (n = 1), atypical choroid plexus papilloma (n = 1) and pilomyxoid astrocytoma (n = 1). Three patients had a non-invasive diagnosis of low-grade glioma. DSC CBV maps of T₁-enhancing tumours were difficult to interpret without the leakage correction. CBV values obtained with and without leakage correction were significantly different (p < 0.01). A significant positive correlation was observed between ASL CBF and DSC CBV (r = 0.516, p = 0.049) which became stronger when leakage correction was applied (r = 0.728, p = 0.002). K₂ values were variable across the group (mean = 0.35, range = -0.49 to 0.64).

CONCLUSION:

CBV values from DSC obtained with and without leakage correction were significantly different. Large increases in CBV were observed following leakage correction in highly T₁-enhancing tumours. DSC and ASL perfusion metrics were found to correlate significantly in a range of paediatric brain tumours. A stronger relationship between DSC and ASL was seen when leakage correction was applied to the DSC data. Leakage correction should be applied when analysing DSC data in enhancing paediatric brain tumours.

ADVANCES IN KNOWLEDGE:

We have shown that leakage correction should be applied when investigating enhancing paediatric brain tumours using DSC-MRI. A stronger correlation was found between CBF derived from ASL and CBV derived from DSC when a leakage correction was employed.

Mapping water exchange across the blood-brain barrier using 3D diffusion-prepared arterial spin labeled perfusion MRI

PURPOSE

To present a novel MR pulse sequence and modeling algorithm to quantify the water exchange rate (k_w ) across the blood-brain barrier (BBB) without contrast, and to evaluate its clinical utility in a cohort of elderly subjects at risk of cerebral small vessel disease (SVD).

METHODS

A diffusion preparation module with spoiling of non-Carr-Purcell-Meiboom-Gill signals was integrated with pseudo-continuous arterial spin labeling (pCASL) and 3D gradient and spin echo (GRASE) readout. The tissue/capillary fraction of the arterial spin labeling (ASL) signal was separated by appropriate diffusion weighting (b = 50 s/mm² ). k_w was quantified using a single-pass approximation (SPA) model with total generalized variation (TGV) regularization. Nineteen elderly subjects were recruited and underwent 2 MRIs to evaluate the reproducibility of the proposed technique. Correlation analysis was performed between k_w and vascular risk factors, Clinical Dementia Rating (CDR) scale, neurocognitive assessments, and white matter hyperintensity (WMH).

RESULTS

The capillary/tissue fraction of ASL signal can be reliably differentiated with the diffusion weighting of b = 50 s/mm² , given ~100-fold difference between the (pseudo-)diffusion coefficients of the 2 compartments. Good reproducibility of k_w measurements (intraclass correlation coefficient = 0.75) was achieved. Average k_w was 105.0 ± 20.6, 109.6 ± 18.9, and 94.1 ± 19.6 min^-1 for whole brain, gray and white matter. k_w was increased by 28.2%/19.5% in subjects with diabetes/hypercholesterolemia. Significant correlations between k_w and vascular risk factors, CDR, executive/memory function, and the Fazekas scale of WMH were observed.

CONCLUSION

A diffusion prepared 3D GRASE pCASL sequence with TGV regularized SPA modeling was proposed to measure BBB water permeability noninvasively with good reproducibility. k_w may serve as an imaging marker of cerebral SVD and associated cognitive impairment.

Blood-ocular barrier disruption in patients with acute stroke

OBJECTIVE

Prompted by the unexpected finding of gadolinium leakage into ocular structures (GLOS) in acute stroke patients, we studied the frequency and nature of this finding in 167 patients.

METHODS

Patients were selected who had an MRI with gadolinium at baseline and another MRI with fluid-attenuated inversion recovery (FLAIR) imaging at 2 and/or 24 hours later. GLOS was detected as lack of vitreous and/or aqueous fluid suppression on postcontrast FLAIR images.

RESULTS

GLOS, evident on postcontrast FLAIR MRI, occurred in 127/167 (76%) patients: 86/109 (79%) patients treated with tissue plasminogen activator and 41/58 (71%) who were untreated. At 2 hours after administration of the contrast, GLOS was more common in the aqueous chamber alone, occurring in 67% of patients, compared to the vitreous chamber alone, seen in 6% of patients; it occurred in both chambers in 27% of patients. At 24 hours, GLOS was present in 121/162 (75%) patients, always involving the vitreous chamber, but also affecting the aqueous chamber in 6% of cases. Vitreous GLOS at 24 hours was associated with increasing age (p = 0.002) and a higher burden of cerebral white matter hyperintensities (p = 0.017). Patients with rapid diffuse GLOS, defined as GLOS involving both chambers at 2 hours, had larger infarcts (p = 0.022) and a higher degree of blood-brain barrier permeability (p = 0.025).

CONCLUSIONS

We found GLOS to be common in patients with acute stroke; delayed GLOS was a marker for chronic vascular disease. The mechanism for acute GLOS remains uncertain but may be a remote effect of acute cerebral injury on the blood-ocular barrier.

White Matter Hyperintensity-Associated Blood-Brain Barrier Disruption and Vascular Risk Factors

BACKGROUND

White matter hyperintensities (WMH), the hallmark of vascular cognitive impairment, are associated with vascular risk factors (VRF). WMH can also be associated with blood-brain barrier (BBB) disruption. The purpose of this study was to look for associations between VRF and BBB disruption in stroke patients with WMH.

METHODS

Magnetic resonance images of stroke patients were reviewed for the presence of WMH. Blood-brain permeability images were retrospectively generated. The degree of BBB permeability was compared with the presence of VRF using logistic regression. Patterns and extent of WMH were classified using Fazekas scores.

RESULTS

Sixty-five patients were included in this study. None of the VRF tested were associated with an increase in BBB disruption. Hypertension was significantly associated with less BBB disruption (P = .04). Nonhypertensive patients in our study had a different pattern of WMH than hypertensive patients, with less involvement of the periventricular white matter.

CONCLUSIONS

We found that in stroke patients with WMH, those with hypertension had less BBB disruption and greater involvement of the periventricular white matter when compared with patients who did not have a history of hypertension. Further investigation is needed to determine if the development of WMH in stroke patients with a history of hypertension has a different pathophysiology from patients who develop WMH in the absence of hypertension.

Identification of Reversible Disruption of the Human Blood-Brain Barrier Following Acute Ischemia

BACKGROUND AND PURPOSE

Animal models of acute cerebral ischemia have demonstrated that diffuse blood-brain barrier (BBB) disruption can be reversible after early reperfusion. However, irreversible, focal BBB disruption in humans is associated with hemorrhagic transformation in patients receiving intravenous thrombolytic therapy. The goal of this study was to use a magnetic resonance imaging biomarker of BBB permeability to differentiate these 2 forms of BBB disruption.

METHODS

Acute stroke patients imaged with magnetic resonance imaging before, 2 hours after, and 24 hours after treatment with intravenous tissue-type plasminogen activator were included. The average BBB permeability of the acute ischemic region before and 2 hours after treatment was calculated using a T2* perfusion-weighted source images. Change in average permeability was compared with percent reperfusion using linear regression. Focal regions of maximal BBB permeability from the pretreatment magnetic resonance imaging were compared with the occurrence of parenchymal hematoma (PH) formation on the 24-hour magnetic resonance imaging scan using logistic regression.

RESULTS

Signals indicating reversible BBB permeability were detected in 18/36 patients. Change in average BBB permeability correlated inversely with percent reperfusion (P=0.006), indicating that early reperfusion is associated with decreased BBB permeability, whereas sustained ischemia is associated with increased BBB disruption. Focal regions of maximal BBB permeability were significantly associated with subsequent formation of PH (P=0.013).

CONCLUSIONS

This study demonstrates that diffuse, mild BBB disruption in the acutely ischemic human brain is reversible with reperfusion. This study also confirms prior findings that focal severe BBB disruption confers an increased risk of hemorrhagic transformation in patients treated with intravenous tissue-type plasminogen activator.

Pretreatment blood-brain barrier disruption and post-endovascular intracranial hemorrhage

OBJECTIVE

This study sought to confirm the relationship between the degree of blood-brain barrier (BBB) damage and the severity of intracranial hemorrhage (ICH) in a population of patients who received endovascular therapy.

METHODS

The degree of BBB disruption on pretreatment MRI scans was analyzed, blinded to follow-up data, in the DEFUSE 2 cohort in which patients had endovascular therapy within 12 hours of stroke onset. BBB disruption was compared with ICH grade previously established by the DEFUSE 2 core lab. A prespecified threshold for predicting parenchymal hematoma (PH) was tested.

RESULTS

Of the 108 patients in the DEFUSE 2 trial, 100 had adequate imaging and outcome data and were included in this study; 24 developed PH. Increasing amounts of BBB disruption on pretreatment MRIs was associated with increasing severity of ICH grade (p = 0.004). BBB disruption on the pretreatment scan was associated with PH (p = 0.020) with an odds ratio for developing PH of 1.69 for each 10% increase in BBB disruption (95% confidence interval 1.09-2.64), although a reliably predictive threshold was not identified.

CONCLUSIONS

The amount of BBB disruption on pretreatment MRI is associated with the severity of ICH after acute intervention. This relationship has now been identified in patients receiving IV, endovascular, and combined therapies. Further study is needed to determine its role in guiding treatment.

MRI-guided selection of patients for treatment of acute ischemic stroke

PURPOSE OF REVIEW

To summarize what is known about the use of MRI in acute stroke treatment (predominantly thrombolysis), to examine the assumptions and theories behind the interpretation of magnetic resonance images of acute ischemic stroke and how they are used to select patients for therapies, and to suggest directions for future research.

RECENT FINDINGS

Recent studies have been contradictory about the usefulness of MRI in selecting patients for treatment. New MRI models for selecting patients have emerged that focus not only on the ischemic penumbra but also on the infarct core. Fixed time-window selection parameters are being replaced by timing-based individualized MRI stroke features. New ways to interpret traditional MRI stroke sequences are emerging.

SUMMARY

Although the efficacy of acute stroke treatment is time dependent, the use of fixed time windows cannot account for individual differences in infarct evolution, which could potentially be detected with MRI. Although MRI shows promise for identifying patients who should be treated, as well as excluding patients who should not be treated, definitive evidence is still lacking. Future research should focus on validating the use of MRI to select patients for intravenous therapies in extended time windows.

Perfusion magnetic resonance imaging: a comprehensive update on principles and techniques

Perfusion is a fundamental biological function that refers to the delivery of oxygen and nutrients to tissue by means of blood flow. Perfusion MRI is sensitive to microvasculature and has been applied in a wide variety of clinical applications, including the classification of tumors, identification of stroke regions, and characterization of other diseases. Perfusion MRI techniques are classified with or without using an exogenous contrast agent. Bolus methods, with injections of a contrast agent, provide better sensitivity with higher spatial resolution, and are therefore more widely used in clinical applications. However, arterial spin-labeling methods provide a unique opportunity to measure cerebral blood flow without requiring an exogenous contrast agent and have better accuracy for quantification. Importantly, MRI-based perfusion measurements are minimally invasive overall, and do not use any radiation and radioisotopes. In this review, we describe the principles and techniques of perfusion MRI. This review summarizes comprehensive updated knowledge on the physical principles and techniques of perfusion MRI.

Pretreatment blood-brain barrier damage and post-treatment intracranial hemorrhage in patients receiving intravenous tissue-type plasminogen activator

BACKGROUND AND PURPOSE

Early blood-brain barrier damage after acute ischemic stroke has previously been qualitatively linked to subsequent intracranial hemorrhage (ICH). In this quantitative study, it was investigated whether the amount of blood-brain barrier damage evident on pre-tissue-type plasminogen activator MRI scans was related to the degree of post-tissue-type plasminogen activator ICH in patients with acute ischemic stroke.

METHODS

Analysis was performed on a database of patients with acute ischemic stroke provided by the Stroke Imaging Repository (STIR) and Virtual International Stroke Trials Archive (VISTA) Imaging Investigators. Patients with perfusion-weighted imaging lesions>10 mL and negative gradient-recalled echo imaging before intravenous tissue-type plasminogen activator were included. Postprocessing of the perfusion-weighted imaging source images was performed to estimate changes in blood-brain barrier permeability within the perfusion deficit relative to the unaffected hemisphere. Follow-up gradient-recalled echo images were reviewed for evidence of ICH and divided into 3 groups according to European Cooperative Acute Stroke Study (ECASS) criteria: no hemorrhage, hemorrhagic infarction, and parenchymal hematoma.

RESULTS

Seventy-five patients from the database met the inclusion criteria, 28 of whom experienced ICH, of which 19 were classified as hemorrhagic infarction and 9 were classified as parenchymal hematoma. The mean permeability (±SDs), expressed as an index of contrast leakage, was 17.0±8.8% in the no hemorrhage group, 19.4±4.0% in the hemorrhagic infarction group, and 24.6±4.5% in the parenchymal hematoma group. Permeability was significantly correlated with ICH grade in univariate (P=0.007) and multivariate (P=0.008) linear regression modeling.

CONCLUSIONS

A perfusion-weighted imaging-derived index of blood-brain barrier damage measured before intravenous tissue-type plasminogen activator is given is associated with the severity of ICH after treatment in patients with acute ischemic stroke.