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Background: Computational fluid dynamics (CFD) allows noninvasive fractional flow (FF) computation in intracranial arterial stenosis. Removal of small artery branches is necessary in CFD simulation. The consequent effects on FF value needs to be judged.Methods: An idealized vascular model was built with 70% focal luminal stenosis. A branch with one third or one half of the radius of the parent vessel was added at a distance of 5, 10, 15 and 20 mm to the lesion. With pressure and flow rate applied as inlet and outlet boundary conditions, CFD simulations were performed. Flow distribution at bifurcations followed Murray's law. By including or removing side branches, five patient-specific intracranial artery models were simulated. Transient simulation was performed on a patient-specific model, with a larger branch for validation. Branching effect was considered trivial if the FF difference between paired models (branches included or removed) was within 5%.Results: Compared with the control model without a branch, in all idealized models the relative differences of FF was within 2%. In five pairs of cerebral arteries (branches included/removed), FFs were 0.876 and 0.877, 0.853 and 0.858, 0.874 and 0.869, 0.865 and 0.858, 0.952 and 0.948. The relative difference in each pair was less than 1%. In transient model, the relative difference of FF was 3.5%.Conclusion: The impact of removing side branches with radius less than 50% of the parent vessel on FF measurement accuracy is negligible in static CFD simulations, and minor in transient CFD simulation. [ABSTRACT FROM AUTHOR]

Background: Cortical microinfarcts (CMIs) have been correlated to cognitive decline and dementia. It was previously considered only visible on microscope, but was recently reported to be visible on 3.0 Tesla magnetic resonance imaging (MRI) and linked to presence of intracranial stenosis. We aimed to investigate CMIs on 3.0 Tesla MRI in patients with M1 middle cerebral artery (MCA-M1) stenosis.Methods: Patients with a recent non-cardioembolic ischemic stroke or transient ischemic attack and an atherosclerotic MCA-M1 stenosis were recruited. The severity of MCA stenosis was defined as moderate (50%-69%) or severe (70%-99% or focal flow void) on time-of-flight MR angiography (MRA). The distal to proximal signal intensity ratio (SIR) of MCA stenosis was measured on time-of-flight MRA to represent its hemodynamic significance. The presence of CMI(s) in the ipsilateral hemisphere was assessed on axial T1- or T2-weighted images and T2-weighted fluid-attenuated inversion-recovery images.Results: Overall, 86 patients (mean age: 62.8 years; 77.9% males) were analyzed, 66 (76.7%) and 20 (23.3%), respectively, having moderate and severe MCA-M1 stenoses. The median SIR was .91. Forty-five (52.3%) patients had ipsilateral CMI(s). Multivariate logistic regression showed a history of dyslipidemia (odds ratio [OR] = 6.83, P = .008), and an SIR lower than the median (OR = 4.73, P = .014) were independently associated with presence of CMI(s) in ipsilateral hemisphere to an MCA-M1 stenosis.Conclusions: Patients with stroke and intracranial stenosis had a high burden of CMI. Except for a history of dyslipidemia, the hemodynamic significance of the arterial stenosis may contribute to the presence of ipsilateral CMI(s) in these patients, which warrants further investigation in prospective, longitudinal studies. [ABSTRACT FROM AUTHOR]

Background: Changes of signal intensities (SIs) across intracranial atherosclerosis (ICAS) on magnetic resonance angiography (MRA) may reflect hemodynamic impact of the lesion. We evaluated the interobserver reproducibility of an index termed signal intensity ratio (SIR), developed in a previous study to represent the changes of SIs across ICAS on MRA. Methods: Symptomatic ICAS on MRA were retrospectively recruited. Two observers respectively evaluated the images and calculated the SIR as follows, blinded to each other's readings: SIR = (mean poststenotic SI − mean background SI)/(mean prestenotic SI − mean background SI). Statistical analyses were performed to evaluate the interobserver reproducibility of this index. Results: A total of 102 symptomatic ICASs were enrolled, with 36 (35.3%) lesions of 50%-69% MRA stenoses and others being 70%-99% stenoses or flow void on MRA. Overall, mean SIRs were not significantly different between the 2 observers (.92 ± .17 versus .93 ± .17; mean difference −.006 ± .09; P = .496 for paired t test). Pearson correlation coefficients were >.80 for all analyses, indicating strong linear correlations between SIRs by the 2 observers. Bland–Altman analysis for SIRs of all cases showed no systematic bias between the 2 observers. For different cut-points ranging from .75 to 1.00, the kappa statistics were mostly greater than .6 and interobserver agreements were all greater than 80%, implying substantial agreement between observers. Conclusions: SIR was demonstrated to be highly reproducible between observers in the present study. Future studies are warranted to further explore the role of this index in comprehensive evaluation and risk stratification of symptomatic ICAS. [Copyright &y& Elsevier]