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Introduction: Based on the Poiseuille’s law (blood flow= [pressure gradient* [Pi*radius 4 ]]/[8*blood viscosity*length]) larger brain arterial diameter should associate with a proportional increase in cerebral blood flow. We have reported that larger brain arterial diameters are associated with higher risk of dementia and cerebrovascular disease, but the flow correlates of larger brain arterial diameters have not been studied. Methods: We leveraged an existing data repository of 325 unselected volunteers recruited to validate phase contrast quantitative magnetic resonance angiography (QMRA). Imaging was performed in a 3.0 Tesla MRI Scanner (Signa VHi to HDx, General Electric Medical Systems, later GE Healthcare, Milwaukee, WI, USA) using either a four-channel or eight-channel neurovascular coil. The volume flow rate measurements were acquired with the Noninvasive Optimal Vessel Analysis software (VasSol,Chicago, IL, USA). Brain arterial diameters of the circle of Willis were measured using LKEB Automated Vessel Analysis (LAVA) software. Adjusted models by age, sex, race/ethnicity and height were built to explore the association between blood flow and the diameters of the basilar, middle, and anterior cerebral arteries. Results: We include 325 participants (mean age 48 ± 15 years, 52% female, 64% non-Hispanic white). As expected, arterial luminal diameters are associated with proportionally higher cerebral blood flow. Among people with the largest diameters in this sample, however, the corresponding cerebral blood flow was lower than predicted[MRS1] and this non-linear association was significant in three out of the five arteries studied (Figure 1). Conclusions: In a sample of relatively healthy individuals, those with the largest diameters had lower-than-expected cerebral blood flow. Further studies are needed to better understand the physiopathology by which larger brain arterial diameters relate to cerebrovascular disease.

Introduction: Embolization reduces flow in cerebral arteriovenous malformations (AVMs) before surgical resection, but changes in pulsatility and resistance indices (PI, RI) are unknown. Here, we measure PI, RI in AVM arterial feeders pre- and post-embolization/surgery. Methods: Records of patients who underwent AVM embolization and surgical resection at our institution between 2007-2014 and had PI, RI, and flows obtained using quantitative magnetic resonance angiography were retrospectively reviewed. PI = [(systolic - diastolic flow velocity)/mean flow velocity] and RI = [(systolic - diastolic flow velocity)/systolic flow velocity]. Hemodynamic parameters were compared between the feeder and contralateral artery pre- and post-embolization/surgery. Results: 32 patients with 48 feeder arteries underwent embolization (mean 1.3 sessions). 32 patients with 49 feeder arteries had surgery with/without preoperative embolization. Before any treatment, flow volume rate and mean, systolic, diastolic flow velocities were significantly higher in feeders versus contralateral counterparts ( P P =0.003, P =0.002). After embolization, flow velocities within feeders were significantly higher than in the normal contralateral vessels, but PI, RI did not change significantly (Table). However, after surgery flow velocities within feeders decreased significantly and PI, RI normalized to match the indices of their contralateral counterparts (Table). Conclusions: Following partial AVM embolization, PI, RI are unchanged and flow velocities in feeder arteries increase significantly likely due to redistribution of flow through residual nidus. Complete surgical resection results in normalization of PI, RI and a concomitant decrease in flow velocities. Table: Changes in PI, RI after embolization and surgery.

Objectives: To determine the effects of degree of stenosis, stenosis length, and residual lumen on intracranial blood flow in patients with extracranial carotid stenosis. Methods: Records of patients who underwent stenting for extracranial carotid stenosis at our institution between 2004-2012 and had flow rates obtained using quantitative magnetic resonance angiography were retrospectively reviewed. Measurements of degree of stenosis, stenosis length, and residual lumen were made from cerebral angiography images. Results: 18 patients had both complete anatomic and flow data available. Mean age was 66 years. Degree of stenosis ranged from 60% to 90%. 61% had symptomatic stenosis. Univariate analysis demonstrated that higher percentage of stenosis and smaller residual lumen (mm) are associated with a significant decrease in ipsilateral internal carotid artery (ICA) flow ( P =0.027 and P =0.007, respectively). Stenosis length (mm) was not significantly associated with ipsilateral ICA flow ( P =0.08). On multiple regression analysis, both degree of stenosis and residual lumen remained predictive of ipsilateral ICA flow ( P =0.005 and P =0.007, respectively). Neither degree of stenosis, stenosis length, or residual lumen were significantly associated with ipsilateral MCA flow (P=0.38, 0.18, and 0.86, respectively), and baseline ICA flow was not predictive of ipsilateral MCA flow ( P =0.37). Conclusions: Degree of stenosis and residual lumen diameter are highly predictive of ICA, but not MCA flow, in the setting of carotid stenosis. Local hemodynamic effects of the stenosis do not translate directly to the distal vasculature, as intracranial flows can be maintained through collateral flow. Figure: Ipsilateral ICA flow and residual lumen. Increasing residual lumen is associated with significant ipsilateral ICA flow increase ( P =0.007, correlation coefficient=0.61).

Objective: Arterio-venous malformations (AVM) feeders are known to remodel with time: increase in diameter when the AVM is present and decrease after the AVM is treated. In this study we used quantitative magnetic resonance angiography (QMRA) to evaluate changes in WSS, flow, and diameter of feeder vessels pre and post treatment with endovascular embolization/ surgery. Methods: 55 patients with AVM were evaluated with QMRA on presentation, 19 patients had QMRA post embolization (1-8 sessions), and 13 post-surgical resection. WSS, flow, and diameter of proximal feeder vessels (MCA, PCA and/or ACA) and their contralateral counterparts were derived from QMRA. These parameters were studied at baseline and compared between the feeder and contralateral artery pre and post embolization/surgery. Results: At baseline, WSS in feeder vessels (n=66) was greater than in the corresponding contralateral vessel (33.55 Dyne/cm2 vs. 24.76 Dyne/cm2; P Conclusion: Arteriovenous malformation feeding vessels are subjected to a higher WSS secondary to higher blood flow. The feeders demonstrate a corresponding enlargement in diameter, as a presumed compensatory response to the high flow. However, the vessel enlargement is insufficient to normalize the WSS at baseline. There was decrease in diameter of the feeder vessel and normalization of the WSS post reduction of blood flow with embolization/surgery.

Objectives: To determine the effects of extracranial carotid stenting on intracranial blood flow. Methods: Records of patients who underwent stenting for extracranial carotid stenosis at our institution between 2004-2012 and had flow rates obtained pre and post stenting using quantitative magnetic resonance angiography were retrospectively reviewed. Measurements of degree of stenosis, stenosis length, and residual lumen were made from cerebral angiography images. Results: 18 patients with complete anatomic and flow data were included. Mean age was 66 years with 61% presenting with symptomatic stenosis. Degree of stenosis ranged from 60% to 90%. Internal carotid artery (ICA) mean flow improved significantly post stenting from 174.9 +/- 83.6 mL/min to 250.7 +/- 91.2 mL/min ( P =0.011). Ipsilateral middle cerebral artery (MCA) flow, however, was not significantly altered post stenting (101.8 +/- 47.7 mL/min vs. 111.3 +/- 37.4 mL/min; P =0.15). Multiple regression analysis revealed that improvement in residual lumen, but not percentage stenosis (p=0.45) or stenosis length (p=0.992), is an independent predictor of increased change in ipsilateral ICA flow ( P =0.005). Degree of stenosis, stenosis length, residual lumen, and ICA flow post-stenting were not predictive of ipsilateral MCA flow ( P =0.65,0.37,0.25,0.79). The ratio of ipsilateral to contralateral ICA flow improved from 0.67 +/- 0.36 at baseline to 0.94 +/- 0.34 after stenting ( P =0.007). The ratio of ipsilateral to contralateral MCA flow was 1.08 +/- 0.59 at baseline, and was unchanged at 1.09 +/- 0.46 after stenting ( P =0.91). Conclusions: ICA flow compromise was evident in the setting of carotid stenosis, which improved by 43% on average post stenting. Improvement in residual lumen at the site of stenosis was the strongest predictor of increased flow, indicating that this parameter is the best indicator of a hemodynamically successful intervention. Unlike ICA flow, intracranial flow measured in the MCA was not significantly compromised at baseline compared to the contralateral hemisphere, nor significantly altered after stenting. This reflects compensatory intracranial collateral supply pre-stenting, which redistributes once the ipsilateral ICA is revascularized.

Objective: To study the hemodynamics of cerebral venous system by evaluation of the internal jugular veins (IJV) using quantitative magnetic resonance angiography (QMRA) in healthy subjects. Methods: 263 healthy subjects (129 females; 134 males; mean age 50 ± 16 years) with no history of cerebrovascular disease were evaluated in supine position with QMRA at 3T. Flow rates of the internal carotid artery (ICA) and vertebral artery (VA) were quantified prospectively with 2D phase contrast MR imaging. IJV flow rates were retrospectively measured from previously acquired 2 D phase contrast imaging of the neck between the C5 and C6 level. Total internal jugular venous flow (TIJVF=LIJV + RIJV) was compared to total cerebral flow (TCBF=ICAs + VAs). Regression analysis was used to examine the effects of age, mean blood pressure (MBP), and other variables on TIJVF. Results: LIJV flow rates (229 ± 141 ml/min) was significantly less than RIJV (362 ± 165 ml/min) (P< 0.0001). TIJVF (592 ± 177 ml/min) was 84% of TCBF (703 ± 115). As expected, TIJVF was significantly dependent on TCBF (p Conclusions: IJVs are the principle outflow pathway of intracranial blood. Reference values for flows in IJVs and TIJVF may help in the evaluation of conditions characterized by venous outflow obstruction (e.g. venous sinus thrombosis or pseudotumor) or excessive venous output (e.g. arterio-venous fistulae or malformations), as well as investigation of conditions hypothesized to be associated cerebral venous insufficiency, such as multiple sclerosis.