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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.

Background Stereotactic radiosurgery (SRS) is a current therapeutic option for treatment of arteriovenous malformations (AVMs) located in deep or eloquent brain regions. Obliteration usually occurs in a delayed fashion, with an expected latency of 3–5 years. Here, we assess how AVM flow correlates with volume before and after SRS treatment. Methods Patients with supratentorial AVM treated with SRS at our institution between 2012–2022 were retrospectively reviewed. Patients were included if Quantitative Magnetic Resonance Angiography (QMRA) study was performed at baseline and at least at the first follow-up. Correlation between AVM flow and volume before and after treatment was evaluated. AVM flow and volume were additionally assessed for obliteration using the non-parametric receiver operating characteristic (ROC) curve. Results Twelve patients with radiologic follow-up imaging were included. Eight patients presented AVM rupture, one of which occurred after radiosurgical treatment. Three patients underwent embolization prior SRS. Mean AVM initial volume was 3.8 cc (0.1–12.4 cc), mean initial flow 174 ml/min (11–604 ml/min), both variables showed progressive reduction at follow-up (range 3–57 months); and flow decreased with volume reduction ( p Conclusions AVM flow significantly decreased after SRS treatment, reflecting volume reduction. Baseline AVM flow and volume both predicted obliteration. QMRA provides additional non-invasive information to monitor patients after radiosurgical treatment.

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.

Object Experimental data about the evolution of intracranial volume and pressure in cases of hydrocephalus are limited due to the lack of available monitoring techniques. In this study, the authors validate intracranial CSF volume measurements within the lateral ventricle, while simultaneously using impedance sensors and pressure transducers in hydrocephalic animals. Methods A volume sensor was fabricated and connected to a catheter that was used as a shunt to withdraw CSF. In vitro bench-top calibration experiments were created to provide data for the animal experiments and to validate the sensors. To validate the measurement technique in a physiological system, hydrocephalus was induced in weanling rats by kaolin injection into the cisterna magna. At 28 days after induction, the sensor was implanted into the lateral ventricles. After sealing the skull using dental cement, an acute CSF drainage/infusion protocol consisting of 4 sequential phases was performed with a pump. Implant location was confirmed via radiography using intraventricular iohexol contrast administration. Results Controlled CSF shunting in vivo with hydrocephalic rats resulted in precise and accurate sensor measurements (r = 0.98). Shunting resulted in a 17.3% maximum measurement error between measured volume and actual volume as assessed by a Bland-Altman plot. A secondary outcome confirmed that both ventricular volume and intracranial pressure decreased during CSF shunting and increased during infusion. Ventricular enlargement consistent with successful hydrocephalus induction was confirmed using imaging, as well as postmortem. These results indicate that volume monitoring is feasible for clinical cases of hydrocephalus. Conclusions This work marks a departure from traditional shunting systems currently used to treat hydrocephalus. The overall clinical application is to provide alternative monitoring and treatment options for patients. Future work includes development and testing of a chronic (long-term) volume monitoring system.

The brainstem auditory evoked response (BAER) is sensitive to pontomesencephalic integrity, transtentorial brain herniation, and at times increased intracranial pressure (ICP). The authors report their experience utilizing a recently described rapid rate, binaural, click and 1,000-Hz tone-burst modification of the BAER (MBAER) in 22 symptomatic non-trauma patients with non-brainstem compressive space-taking cerebral lesions. The majority presented with mild to moderate clinical signs suggestive of increased ICP, and focal neurological deficits. The cerebral lesions, mostly tumors (17), averaged 4-5 cm in diameter, with radiological signs of mass effect such as flattening of the sulci, midline shift, and narrowing of the basal cisterns. A number of significant changes in Wave V and V (n) latency and less so amplitude were found in patients compared with age-matched normal volunteers, as well as those again studied after surgical decompression. Similar MBAER changes had been noted in normal volunteers placed in a dependent head position. Possible mechanisms to explain these findings are discussed. The methodology shows promise and if combined with automated peak recognition could make Neuro ICU monitoring practical.

Software tools that utilize haptics for sculpting precise fitting cranial implants are utilized in an augmented reality immersive system to create a virtual working environment for the modelers. The virtual environment is designed to mimic the traditional working environment as closely as possible, providing more functionality for the users. The implant design process uses patient CT data of a defective area. This volumetric data is displayed in an implant modeling tele-immersive augmented reality system where the modeler can build a patient specific implant that precisely fits the defect. To mimic the traditional sculpting workspace, the implant modeling augmented reality system includes stereo vision, viewer centered perspective, sense of touch, and collaboration. To achieve optimized performance, this system includes a dual-processor PC, fast volume rendering with three-dimensional texture mapping, the fast haptic rendering algorithm, and a multi-threading architecture. The system replaces the expensive and time consuming traditional sculpting steps such as physical sculpting, mold making, and defect stereolithography. This augmented reality system is part of a comprehensive tele-immersive system that includes a conference-room-sized system for tele-immersive small group consultation and an inexpensive, easily deployable networked desktop virtual reality system for surgical consultation, evaluation and collaboration. This system has been used to design patient-specific cranial implants with precise fit.

Ventriculostomy is a neurosurgical procedure that consists of the insertion of a catheter into the ventricles of the brain for relieving the intracranial pressure. A distinct "popping" sensation is felt as the catheter enters the ventricles. Early ventriculostomy simulators provided some basic audio/visual feedback to simulate the procedure, displaying a 3D virtual model of a human head. Without any tactile feedback, the usefulness of such simulators was very limited. The first generation haptic ventriculostomy simulators incorporated a haptic device to generate a virtual resistance and "give" upon ventricular entry. While this created considerable excitement as a novelty device for cannulating ventricles, its usefulness for teaching and measuring neurosurgical expertise was still very limited. Poor collocation between the haptic device stylus held by the surgeon and the visual representation of the virtual catheter, as well as the lack of a correct viewer-centered perspective, created enormous confusion for the neurosurgeons who diverted their attention from the actual ventriculostomy procedure to overcoming the limitations of the simulator. We present a second generation haptic ventriculostomy simulator succeeding over the major first generation limitations by introducing a head and hand tracking system as well as a high-resolution high-visual-acuity stereoscopic display to enhance the perception and realism of the virtual ventriculostomy.