| Background and purpose—Fractional flow reserve(FFR)has exceled the degree of stenosis and become the new guiding post for identifying functionally severe coronary artery lesions.In the current study,we utilized a similar index,fractional flow(FF),to gauge the hemodynamic impact of symptomatic intracranial atherosclerotic stenosis(ICAS),and to clarify its relationships with the severity of stenosis and collateral status.Methods—Patients with ?70% stenosis considered as potential candidates for endovascular intervention had been consecutively recruited in our center.FF,defining the ratio of the distal pressure measured by the pressure wire(Pd)to the aortic pressure measured by the guiding catheter(Pa),was measured during the endovascular procedure.The degree of stenosis is reviewed by a blinded interventional neurologist using the Warfarin-Aspirin Symptomatic Intracranial Disease(WASID)method.All the enrolled patients should undergo CT perfusion examination before endovascular measurement within three days.Patients' demographics,past history,vascular risk factors,clinical information,chemical examinations and imaging features and collateral status were also collected.Pearson correlation analysis was used to analysis the relationship between degree/length of stenosis,the parameters of CTP and fractional flow in the affected vessel.Patients were divided into two groups,fractional flow and anatomical stenosis matched group and fractional flow and anatomical stenosis mismatched group.The related factors was analyzed between the two groups.Results—25 patients were analyzed in our study finally.The cohort consisted of 15(60%)men,with mean age of 55.6(median,55;range,50.5-62)years.19(76%)patients presented with ischemic stroke,and the rest with TIA.Confirmed by DSA examination,6 patients(24%)of relevant vessel located in the middle cerebral artery M1 portion,5 patients(20%)in internal cerebral artery C6-7 portion,8(32%)in vertebral artery V4 portion and 6(24%)in basilar artery.FF was negative correlation with r MTT(r=-0.453,95% CI(-791,-.001),P=0.023)and r TTP(r=-0.4,95% CI(-0.753,-.001),P.048),but didn't show significant statistical correlation with r CBF and r CBV.Regardless of the grades of circulation,as the rate of stenosis increasing,there was a decending trend of fraction flow,but without statistical significance(r=-0.398,95% CI(-.699,-.027).With regard of collaterals,fractional flow was significantly related to severity of stenosis in the patients with poor collateral circulation(r=-0.677,95% CI(-.902,-.235),P=0.032),but not for patients with good collateral circulation(r=-0.279,95% CI(-.798,.346),P=0.356).In analyzing the related factors between matched and mismatched groups,14 patients were recognized as matched group,and 11 patients were mismatched group.Glucose was related with matched group.However,collateral status and LDP may have the trend of relationship with matched group,without statistical significance.Conclusions—An anatomically severe(70-99%)symptomatic ICAS lesion may lay significant hemodynamic stress downstream as assessed by the index FF.Fractional flow may be an appropriate indicator reflecting the functional significance of intracranial stenosis to downstream perfusion.However,a good collateral circulation may mitigate such hemodynamic impact,which may partly explain the protective effect of good collaterals against recurrent stroke in such patients.Background and purpose—Fractional flow(FF)has become the new guiding post for identifying functionally severe coronary artery lesions and renal artery stenosis,which is introduced to quantitatively assess the hemodynamics significance of severe intracranial stenosis.A computational fluid dynamics(CFD)based method is proposed to non-invasively compute the FFCFD and compared against FF measured by an invasive technique.Methods—Enrolled patients came from part 1(described detailed previously).Eleven patients with severe intracranial stenosis considered for endovascular intervention were recruited and an invasive procedure was performed to measure the distal and the aortic pressure(Pa and Pd).The FF was calculated as Pd/Pa.The computed tomography angiography(CTA)was used to reconstruct three-dimensional(3D)arteries for each patient.Cerebral hemodynamics was then computed for the arteries using a mathematical model governed by Navier-Stokes equations and with the outflow conditions imposed by a model of distal resistance and compliance.The non-invasive Pa CFD,Pd CFD an FFCFD were then obtained from the CFD calculation using a 16-core parallel computer.Spearmann correlation analysis was used to analysis the Consistency between invasive and non-invasive parameters.Results—Eleven patients with sixteen imaging were analyzed in this study finally.The cohort consisted of 6(54.5%)men,with mean age of 58.6years old.Confirmed by DSA examination,2 patients(18.2%)of relevant vessel located in the middle cerebral artery M1 portion,3 patients(27.3%)in internal cerebral artery C6-7 portion,5(45.5%)in vertebral artery V4 portion and 1(9.1%)in basilar artery.The computed pressure ratios are highly correlated with the ones measured by the pressure wires(V=0.88,p<0.001)and the difference is approximately 6.07%.The numerical simulation results also revealed a significant relationship(r=0.68,p=0.0019)between the pressure ratios and the computed carotid artery(inlet)blood flow which is however less correlated with the percentage of stenosis(r=-0.59,p=0.009).Conclusions—Fraction flow can be obtained invasively or non-invasively and we show that the parameter reflects the hemodynamic significance of the stenosis.A CFD based method is proposed to compute FF,and the value of the computed FFCFD is close to the value obtained with the invasive measurement.This CFD based method is therefore be potentially useful in the non-invasive assessment of the functional alteration caused by cerebral luminal stenosis.The numerical simulation also helps in elucidating that the pressure ratio is more closely related to the hemodynamics than the percentage of stenosis. |
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