Historically, the blood-brain barrier (BBB) was considered to be at the level of cerebral endothelium. Currently, the interaction of endothelium with other components of the vessel wall and with neurones and glial cells is considered to constitute a functional unit, termed the neurovascular unit that maintains cerebral homeostasis in steady states and brain injury. The emphasis of this review is on cerebral endothelium, the best-studied component of the neurovascular unit, and its permeability mechanisms in health and acute brain injury. Major advances have been made in unravelling the molecular structure of caveolae and tight junctions, both of which are components of the structural barrier to the entry of plasma proteins into brain. Time course studies suggest that caveolar changes precede junctional changes in acute brain injury. Additional factors modulating BBB permeability in acute brain injury are matrix metalloproteinases-2 and 9 and angiogenic factors, the most notable being vascular endothelial growth factor-A and angiopoietins (Ang) 1 and 2. Vascular endothelial growth factor-A and Ang2 have emerged as potent inducers of BBB breakdown while Ang1 is a potent anti-leakage factor. These factors have the potential to modulate permeability in acute brain injury and this is an area of ongoing research. Overall, a combination of haemodynamic, structural and molecular alterations affecting brain endothelium results in BBB breakdown in acute brain injury.

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BackgroundMRI-guided focused ultrasound (MRgFUS) thalamotomy is a promising non-invasive treatment option for medication-resistant essential tremor. However, it has been associated with variable efficacy and a relatively high incidence of adverse effects.ObjectivesTo assess the evolution of radiological findings after MRgFUS thalamotomy and to evaluate their significance for clinical outcomes.MethodsNinety-four patients who underwent MRgFUS between 2012 and 2017 were retrospectively evaluated. Lesion characteristics were assessed on routine MRI sequences, as well as with tractography. Relationships between imaging appearance, extent of white matter tract lesioning (59/94, on a 4-point scale) and clinical outcome were investigated. Recurrence was defined as >33% loss of tremor suppression at 3 months relative to day 7.ResultsAcute lesions demonstrated blood products, surrounding oedema and peripheral diffusion restriction. The extent of dentatorubrothalamic tract (DRTT) lesioning was significantly associated with clinical improvement at 1 year (t=4.32, p=0.001). Lesion size decreased over time (180.8±91.5 mm3 at day 1 vs 19.5±19.3 mm3 at 1-year post-treatment). Higher post-treatment oedema (t=3.59, p<0.001) was associated with larger lesions at 3 months. Patients with larger lesions at day 1 demonstrated reduced rates of tremor recurrence (t=2.67, p=0.019); however, lesions over 170 mm3 trended towards greater incidence of adverse effects (sensitivity=0.60, specificity=0.63). Lesion encroachment on the medial lemniscus (Sn=1.00, Sp=0.32) and pyramidal tract (Sn=1.00, Sp=0.12) were also associated with increased adverse effects incidence.ConclusionLesion size at day 1 predicts symptom recurrence, with fewer recurrences seen with larger lesions. Greater DRTT lesioning is associated with treatment efficacy. These findings may have implications for lesion targeting and extent.Trial registration numberNCT02252380.

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Object Atrophy in specific brain areas correlates with poor neuropsychological outcome after subarachnoid hemorrhage (SAH). Few studies have compared global atrophy in SAH with outcome. The authors examined the relationship between global brain atrophy, clinical factors, and outcome after SAH. Methods This study was a post hoc exploratory analysis of the Clazosentan to Overcome Neurological Ischemia and Infarction Occurring After Subarachnoid Hemorrhage (CONSCIOUS-1) trial, a randomized, double-blind, placebo-controlled trial of 413 patients with aneurysmal SAH. Patients with infarctions or areas of encephalomalacia on CT, and those with large clip/coil artifacts, were excluded. The 97 remaining patients underwent CT at baseline and 6 weeks, which was analyzed using voxel-based volumetric measurements. The percentage difference in volume between time points was compared against clinical variables. The relationship with clinical outcome was modeled using univariate and multivariate analysis. Results Older age, male sex, and systemic inflammatory response syndrome (SIRS) during intensive care stay were significantly associated with brain atrophy. Greater brain atrophy was significantly associated with poor outcome on the modified Rankin scale (mRS), severity of deficits on the National Institutes of Health Stroke Scale (NIHSS), worse executive functioning, and lower EuroQol Group–5D (EQ-5D) score. Adjusted for confounders, brain atrophy was not significantly associated with Mini-Mental State Examination and Functional Status Examination scores. Brain atrophy was not associated with angiographic vasospasm or delayed ischemic neurological deficit. Conclusions Worse mRS score, NIHSS score, executive functioning, and EQ-5D scores were associated with greater brain atrophy and older age, male sex, and SIRS burden. These data suggest outcome is associated with factors that cause global brain injury independent of focal brain injury.

Intravoxel incoherent motion (IVIM) is a magnetic resonance imaging (MRI) technique that is seeing increasing use in neuro-oncology and offers an alternative to contrast-enhanced perfusion techniques for evaluation of tumor blood volume after stereotactic radiosurgery (SRS). To date, IVIM has not been validated against contrast enhanced techniques for brain metastases after SRS. In the present study, we measure blood volume for 20 brain metastases (15 patients) at baseline, 1 week and 1 month after SRS using IVIM and dynamic contrast enhanced (DCE)-MRI. Correlation between blood volume measurements made with IVIM and DCE-MRI show poor correlation at baseline, 1 week, and 1 month post SRS (r = 0.33, 0.14 and 0.30 respectively). At 1 week after treatment, no significant change in tumor blood volume was found using IVIM or DCE-MRI (p = 0.81 and 0.41 respectively). At 1 month, DCE-MRI showed a significant decrease in blood volume (p = 0.0002). IVIM, on the other hand, demonstrated the opposite effect and showed a significant increase in blood volume at 1 month (p = 0.03). The results of this study indicate that blood volume measured with IVIM and DCE-MRI are not equivalent. While this may relate to differences in the type of perfusion information each technique is providing, it could also reflect a limitation of tumor blood volume measurements made with IVIM after SRS. IVIM measurements of tumor blood volume in the month after SRS should therefore be interpreted with caution.

Blood-brain barrier (BBB) breakdown to plasma proteins leads to vasogenic edema which when diffuse is a life threatening complication in many types of acute brain injury. In our previous studies, early BBB breakdown was associated with increased expression of endothelial caveolin-1α (Cav-1) protein and decreased expression of occludin. In order to attenuate these changes, the effects of intra-cortical angiopoietin-1 (Ang1), a potent anti-permeability factor, on BBB breakdown was assessed in the cold injury model at day 1 post-injury. Overall vascular permeability at the lesion site was assessed in Ang1 non-treated and treated cold-injured rats, using horseradish peroxidase (HRP) as a tracer and in individual vessels by dual labeling immunofluorescence for Cav-1 or occludin and fibronectin, a marker of BBB breakdown. In addition, Cav-1, occludin, Akt, and ERK1/2 expression at the lesion site was detected by immunoblotting. Non-treated cold-injured rats showed focal HRP leakage at the lesion site which was significantly decreased (P < 0.001) in the Ang1-treated group. Increased endothelial Cav-1 and decreased occludin immunoreactivity was observed in arterioles and corresponding-sized venules with BBB breakdown in the non-treated cold-injured rats, and similar expression of these proteins was detected at the lesion site by immunoblotting associated with increased expression of Akt and ERK2 proteins. These alterations were attenuated by Ang1 treatment which resulted in Cav-1, occludin, Akt, and ERK1/2 protein expression that was similar to that of the control groups as was the endothelial Cav-1 and occludin immunoreactivity in leaky vessels. These data suggest that Ang1 administered early post-injury has potential in attenuating the degree of vascular alterations and subsequent vasogenic edema.

BACKGROUND AND PURPOSE: MR imaging rescans and recalls can create large hospital revenue loss. The purpose of this study was to develop a fast, automated method for assessing rescan need in motion-corrupted brain series. MATERIALS AND METHODS:A deep learning-based approach was developed, outputting a probability for a series to be clinically useful. Comparison of this per-series probability with a threshold, which can depend on scan indication and reading radiologist, determines whether a series needs to be rescanned. The deep learning classification performance was compared with that of 4 technologists and 5 radiologists in 49 test series with low and moderate motion artifacts. These series were assumed to be scanned for 2 scan indications: screening for multiple sclerosis and stroke. RESULTS:The image-quality rating was found to be scan indication-and reading radiologist-dependent. Of the 49 test datasets, technologists created a mean ratio of rescans/recalls of (4.7 Ϯ 5.1)/(9.5 Ϯ 6.8) for MS and (8.6 Ϯ 7.7)/(1.6 Ϯ 1.9) for stroke. With thresholds adapted for scan indication and reading radiologist, deep learning created a rescan/recall ratio of (7.3 Ϯ 2.2)/(3.2 Ϯ 2.5) for MS, and (3.6 Ϯ 1.5)/(2.8 Ϯ 1.6) for stroke. Due to the large variability in the technologists' assessments, it was only the decrease in the recall rate for MS, for which the deep learning algorithm was trained, that was statistically significant (P ϭ .03). CONCLUSIONS:Fast, automated deep learning-based image-quality rating can decrease rescan and recall rates, while rendering them technologist-independent. It was estimated that decreasing rescans and recalls from the technologists' values to the values of deep learning could save hospitals $24,000/scanner/year. ABBREVIATIONS: CB ϭ clinically bad; CG ϭ clinically good; CNN ϭ convolutional neural network; DL ϭ deep learning; D0 -D5 ϭ radiologists; IQ ϭ image quality; R0 ϭ radiologist; ROC ϭ receiver operating characteristic; T1-T4 ϭ MR imaging technologists