Quantitative common carotid artery blood flow: Prediction of internal carotid artery stenosis

Vasa vasorum interna in the carotid wall of active forms of Takayasu arteritis evidenced by ultrasound localization microscopy

Introduction: Takayasu arteritis (TA) is associated with microvascularization of the wall of large arteries and is related to inflammation. Ultrasound localization microscopy (ULM), combining ultrafast ultrasound imaging with microbubble (MB) injection, can track the path of MBs within the arterial wall and thus provide imaging of the vasa vasorum. From the analysis of MB tracks in the common carotid arteries of patients with active TA, we report the presence of microvessels in connection with the carotid lumen (i.e., vasa vasorum interna [VVI]). Methods: ULM maps were obtained on five patients with active disease in the observational single-center series of the TAK-UF study. MB tracks connected to the carotid lumen were automatically identified, allowing the reconstruction of VVI. Results: MB tracking allows us to observe a microvascular network on the inner part of the wall, with some vessels in communication with the carotid lumen. This type of vessel was identified in all patients with active TA (n = 5) with a median of 2.2 [1.1-3.0] vessels per acquisition (2D longitudinal view of 3 cm of the common carotid artery). The blood flow within these vessels is mainly centrifugal; that is, toward the adventitia (88% [54-100] of MB tracks with flow directed to the outer part of the wall). Conclusion: VVI are present in humans in the case of active TA and emphasize the involvement of the intima in the pathological process. ClinicalTrials.gov Identifier: NCT03956394.

Cardiac dimensions and hemodynamics in healthy juvenile Landrace swine

BACKGROUND

Swine are frequently used as animal model for cardiovascular research, especially in terms of representativity of human anatomy and physiology. Reference values for the most common species used in research are important for planning and execution of animal testing. Transesophageal echocardiography is the gold standard for intraoperative imaging, but can be technically challenging in swine. Its predecessor, epicardial echocardiography (EE), is a simple and fast intraoperative imaging technique, which allows comprehensive and goal-directed assessment. However, there are few echocardiographic studies describing echocardiographic parameters in juvenile swine, none of them using EE. Therefore, in this study, we provide a comprehensive dataset on multiple geometric and functional echocardiographic parameters, as well as basic hemodynamic parameters in swine using EE.

METHODS

The data collection was performed during animal testing in ten female swine (German Landrace, 104.4 ± 13.0 kg) before left ventricular assist device implantation. Hemodynamic data was recorded continuously, before and during EE. The herein described echocardiographic measurements were acquired according to a standardized protocol, encompassing apical, left ventricular short axis and long axis as well as epiaortic windows. In total, 50 echocardiographic parameters and 10 hemodynamic parameters were assessed.

RESULTS

Epicardial echocardiography was successfully performed in all animals, with a median screening time of 14 min (interquartile range 11-18 min). Referring to left ventricular function, ejection fraction was 51.6 ± 5.9% and 51.2 ± 6.2% using the Teichholz and Simpson methods, respectively. Calculated ventricular mass was 301.1 ± 64.0 g, as the left ventricular end-systolic and end-diastolic diameters were 35.3 ± 2.5 mm and 48.2 ± 3.5 mm, respectively. The mean heart rate was 103 ± 28 bpm, mean arterial pressure was 101 ± 20 mmHg and mean flow at the common carotid artery was 627 ± 203 mL/min.

CONCLUSION

Epicardial echocardiography allows comprehensive assessment of most common echocardiographic parameters. Compared to humans, there are important differences in swine with respect to ventricular mass, size and wall thickness, especially in the right heart. Most hemodynamic parameters were comparable between swine and humans. This data supports study planning, animal and device selection, reinforcing the three R principles in animal research.

Hemodynamic characteristics in a cerebral aneurysm model using non-Newtonian blood analogues

This study aims to develop an experimentally validated computational fluid dynamics (CFD) model to estimate hemodynamic characteristics in cerebral aneurysms (CAs) using non-Newtonian blood analogues. Blood viscosities varying with shear rates were measured under four temperatures first, which serves as the reference for the generation of blood analogues. Using the blood analogue, particle image velocimetry (PIV) measurements were conducted to quantify flow characteristics in a CA model. Then, using the identical blood properties in the experiment, CFD simulations were executed to quantify the flow patterns, which were used to compare with the PIV counterpart. Additionally, hemodynamic characteristics in the simplified Newtonian and non-Newtonian models were quantified and compared using the experimentally validated CFD model. Results showed the proposed non-Newtonian viscosity model can predict blood shear-thinning properties accurately under varying temperatures and shear rates. Another developed viscosity model based on the blood analogue can well represent blood rheological properties. The comparisons in flow characteristics show good agreements between PIV and CFD, demonstrating the developed CFD model is qualified to investigate hemodynamic factors within CAs. Furthermore, results show the differences of absolute values were insignificant between Newtonian and non-Newtonian fluids in the distributions of wall shear stress (WSS) and oscillatory shear index (OSI) on arterial walls. However, not only does the simplified Newtonian model underestimate WSS and OSI in most regions of the aneurysmal sac, but it also makes mistakes in identifying the high OSI regions on the sac surface, which may mislead the hemodynamic assessment on the pathophysiology of CAs.

Multicomponent material property characterization of atherosclerotic human carotid arteries through a Bayesian Optimization based inverse finite element approach

OBJECTIVE

Plaque rupture in atherosclerotic carotid arteries is a main cause of ischemic stroke and it is correlated with high plaque stresses. Hence, analyzing stress patterns is essential for plaque specific rupture risk assessment. However, the critical information of the multicomponent material properties of atherosclerotic carotid arteries is still lacking greatly. This work aims to characterize component-wise material properties of atherosclerotic human carotid arteries under (almost) physiological loading conditions.

METHODS

An inverse finite element modeling (iFEM) framework was developed to characterize fibrous intima and vessel wall material properties of 13 cross sections from five carotids. The novel pipeline comprised ex-vivo inflation testing, pre-clinical high frequency ultrasound for deriving plaque deformations, pre-clinical high-magnetic field magnetic resonance imaging, finite element modeling, and a sample efficient machine learning based Bayesian Optimization.

RESULTS

The nonlinear Yeoh constants for the fibrous intima and wall layers were successfully obtained. The optimization scheme of the iFEM reached the global minimum with a mean error of 3.8% in 133 iterations on average. The uniqueness of the results were confirmed with the inverted Gaussian Process (GP) model trained during the iFEM protocol.

CONCLUSION

The developed iFEM approach combined with the inverted GP model successfully predicted component-wise material properties of intact atherosclerotic human carotids ex-vivo under physiological-like loading conditions.

SIGNIFICANCE

We developed a novel iFEM framework for the nonlinear, component-wise material characterization of atherosclerotic arteries and utilized it to obtain human atherosclerotic carotid material properties. The developed iFEM framework has great potential to be advanced for patient-specific in-vivo application.

Common Carotid Artery Volume Flow: A Comparison Study between Ultrasound Vector Flow Imaging and Phase Contrast Magnetic Resonance Imaging

Volume flow estimation in the common carotid artery (CCA) can assess the absolute hemodynamic effect of a carotid stenosis. The aim of this study was to compare a commercial vector flow imaging (VFI) setup against the reference method magnetic resonance phase contrast angiography (MRA) for volume flow estimation in the CCA. Ten healthy volunteers were scanned with VFI and MRA over the CCA. VFI had an improved precision of 19.2% compared to MRA of 31.9% (p = 0.061). VFI estimated significantly lower volume flow than MRA (mean difference: 63.2 mL/min, p = 0.017), whilst the correlation between VFI and MRA was strong (R² = 0.81, p < 0.0001). A Bland–Altman plot indicated a systematic bias. After bias correction, the percentage error was reduced from 41.0% to 25.2%. This study indicated that a VFI setup for volume flow estimation is precise and strongly correlated to MRA volume flow estimation, and after correcting for the systematic bias, VFI and MRA become interchangeable.

A System for Continuous Pre- to Post-reperfusion Intra-carotid Cold Infusion for Selective Brain Hypothermia in Rodent StrokeModels

Intra-carotid cold infusion (ICCI) appears as a promising method for hypothermia-mediated brain protection from ischemic stroke. Recent clinical pilot studies indicate easy implementation of ICCI into endovascular acute ischemic stroke treatment. Current rodent ICCI-in-stroke models limit ICCI to the post-reperfusion phase. To establish a method for continuous ICCI over the duration of intra-ischemia to post-reperfusion in rodent stroke models, a novel system was developed. Eighteen male Sprague-Dawley rats were included. Intraluminal filament method was used for transient middle cerebral artery occlusion (MCAO). Normal saline (~ 0 °C) was delivered (≤ 2.0 mL/min) into the internal carotid artery via a customized infusion system without interruption during MCAO (intra-ischemia) to after filament withdrawal (post-reperfusion). Bilateral cortical and striatal temperatures were monitored. Hypothermia goals were a temperature reduction in the ischemic hemisphere by 2 °C prior to reperfusion and thereafter maintenance of regional brain hypothermia at ~ 32 °C limiting the administered ICCI volume to ½ of each rat's total blood volume. During ischemia, maximum brain cooling rate was achieved with ICCI at 0.5 mL/min. It took 2 min to reduce ischemic striatal temperature by 2.3 ± 0.3 °C. After reperfusion, brain cooling was continued at 2 mL/min ICCI first (over 42 s) and maintained at 32.1 ± 0.3 °C at 0.7 mL/min ICCI over a duration of 15 ± 0.8 min. ICCI (total 12.6 ± 0.6 mL) was uninterrupted over the duration of the studied phases. First system that allows continuous ICCI during the phases of intra-ischemia to post-reperfusion in small animals for selective brain cooling and for investigations of other neuroprotective infusions.

Flow with variable pulse frequencies accelerates vascular recellularization and remodeling of a human bioscaffold

Despite significant advances in vascular tissue engineering, the ideal graft has not yet been developed and autologous vessels remain the gold standard substitutes for small diameter bypass procedures. Here, we explore the use of a flow field with variable pulse frequencies over the regeneration of an ex vivo-derived human scaffold as vascular graft. Briefly, human umbilical veins were decellularized and used as scaffold for cellular repopulation with human smooth muscle cells (SMC) and endothelial cells (EC). Over graft development, the variable flow, which mimics the real-time cardiac output of an individual performing daily activities (e.g., resting vs. exercising), was implemented and compared to the commonly used constant pulse frequency. Results show marked differences on SMC and EC function, with changes at the molecular level reflecting on tissue scales. First, variable frequencies significantly increased SMC proliferation rate and glycosaminoglycan production. These results can be tied with the SMC gene expression that indicates a synthetic phenotype, with a significant downregulation of myosin heavy chain. Additionally and quite remarkably, the variable flow frequencies motivated the re-endothelialization of the grafts, with a quiescent-like structure observed after 10 days of conditioning, contrasting with the low surface coverage and unaligned EC observed under constant frequency (CF). Besides, the overall biomechanics of the generated grafts (conditioned with both pulsed and CFs) evidence a significant remodeling after 55 days of culture, depicted by high burst pressure and Young's modulus. These last results demonstrate the positive recellularization and remodeling of a human-derived scaffold toward an arterial vessel.

Reduced patency in left-sided arteriovenous grafts in a porcine model

OBJECTIVE

The porcine arteriovenous graft model is commonly used to study hemodialysis vascular access failure, with most studies using a bilateral, paired-site approach in either the neck or femoral vessels. In humans, left- and right-sided central veins have different anatomy and diameters, and left-sided central vein catheters have worse outcomes. We assessed the effect of laterality on arteriovenous prosthetic graft patency and hypothesized that left-sided carotid-jugular arteriovenous prosthetic grafts have reduced patency in the porcine model.

METHODS

Arteriovenous polytetrafluoroethylene grafts were placed ipsilaterally or bilaterally in 10 Yorkshire male pigs from the common carotid artery to the internal jugular vein. Ultrasound measurements of blood flow velocities and diameters were assessed before graft placement. Animals were sacrificed at 1 week, 2 weeks, or 3 weeks. Patency was determined clinically; grafts and perianastomotic vessels were excised and analyzed with histology and immunostaining.

RESULTS

At baseline, left- and right-sided veins and arteries had similar blood flow velocities. Although internal jugular veins had similar diameters at baseline, left-sided carotid arteries had 11% smaller outer diameters (P = .0354). There were 10 left-sided and 8 right-sided polytetrafluoroethylene grafts placed; only 4 of 10 (40%) grafts were patent on the left compared with 7 of 8 (88%) grafts patent on the right (P = .04). Left-sided grafts had increased macrophages at the arterial anastomosis (P = .0007). Left-sided perianastomotic arteries had thicker walls (0.74 vs 0.60 mm; P = .0211) with increased intima-media area (1.14 vs 0.77 mm²; P = .0169) as well as a trend toward 38% smaller luminal diameter (1.6 vs 2.5 mm; P = .0668) and 20% smaller outer diameter (3.0 vs 3.7 mm; P = .0861). Left- and right-sided perianastomotic veins were similar histologically, but left-sided veins had decreased expression of phosphorylated endothelial nitric oxide synthase (P = .0032) and increased numbers of α-actin-positive smooth muscle cells (P = .0022).

CONCLUSIONS

Left-sided arteriovenous grafts are associated with reduced short-term patency compared with right-sided grafts in the Yorkshire pig preclinical model of arteriovenous prosthetic grafts. Laterality must be considered in planning and interpreting surgical preclinical models.

Off-Label Application of Pipeline Embolization Device for Intracranial Aneurysms

PURPOSE

The Pipeline embolization device (PED) is approved in the USA for treating giant and large aneurysms arising from the petrous to superior hypophyseal segments of the internal carotid artery in patients older than 21 years of age. This study investigates off-label PED results in a large cohort.

MATERIALS AND METHODS

Retrospective, single-center review of all patients who had off-label PED surgery.

RESULTS

Sixty-two aneurysms (48 patients) underwent off-label PED treatment from 2012- 2017. There were 44 females and four males (age 21 to 75 years; mean/median, 54.3/55.0 years). The most common presenting symptom was headache (47/62, 75.8%). All aneurysms were in the anterior circulation. Aneurysm size ranged from 1.4 to 25.0 mm (mean/median, 7.6/6.9 mm). Fifty-two aneurysms had post-operative imaging with total/near-complete occlusion of 84.6% (44/52). Aneurysm-based operative near-term complication rate was 9.7% while there were no permanent complications. For aneurysms and headache, 86.7% improved/resolved after embo-surgery, and were four times more likely to have a better clinical outcome (resolved or improved symptoms) after surgery (odds ratio [OR], 4.333; P=0.0325). Left-sided aneurysms had a higher occlusion rate (OR, 20; P=0.0073). Hypertension (OR, 4.2; P=0.0332) and smoking (OR, 7; P=0.0155) were more prone towards aneurysm occlusion. Patients without a family history were 14 times more likely to have favorable imaging outcome (P=0.0405). There is no difference of occlusion rates between untreated and previously treated aneurysms (P=0.6894). Overall, occlusion rate decreased by 14% with an increase of aneurysm size by 1 mm (P=0.0283).

CONCLUSION

For anterior circulation aneurysms, the off-label application of PED is as effective and safe as reported for on-label intracranial aneurysms.

Elucidating the role of graft compliance mismatch on intimal hyperplasia using an ex vivo organ culture model

There is a growing clinical need to address high failure rates of small diameter (<6 mm) synthetic vascular grafts. Although there is a strong empirical correlation between low patency rates and low compliance of synthetic grafts, the mechanism by which compliance mismatch leads to intimal hyperplasia is poorly understood. To elucidate this relationship, synthetic vascular grafts were fabricated that varied compliance independent of other graft variables. A computational model was then used to estimate changes in fluid flow and wall shear stress as a function of graft compliance. The effect of compliance on arterial remodeling in an ex vivo organ culture model was then examined to identify early markers of intimal hyperplasia. The computational model prediction of low wall shear stress of low compliance grafts and clinical control correlated well with alterations in arterial smooth muscle cell marker, extracellular matrix, and inflammatory marker staining patterns at the distal anastomoses. Conversely, high compliance grafts displayed minimal changes in fluid flow and arterial remodeling, similar to the sham control. Overall, this work supports the intrinsic link between compliance mismatch and intimal hyperplasia and highlights the utility of this ex vivo organ culture model for rapid screening of small diameter vascular grafts. STATEMENT OF SIGNIFICANCE: We present an ex vivo organ culture model as a means to screen vascular grafts for early markers of intimal hyperplasia, a leading cause of small diameter vascular graft failure. Furthermore, a computational model was used to predict the effect of graft compliance on wall shear stress and then correlate these values to changes in arterial remodeling in the organ culture model. Combined, the ex vivo bioreactor system and computational model provide insight into the mechanistic relationship between graft-arterial compliance mismatch and the onset of intimal hyperplasia.

A biophysical vascular bubble model for devising decompression procedures

Vascular bubble models, which present a realistic biophysical approach, hold great promise for devising suitable diver decompression procedures. Nanobubbles were found to nucleate on a flat hydrophobic surface, expanding to form bubbles after decompression. Such active hydrophobic spots (AHS) were formed from lung surfactants on the luminal aspect of ovine blood vessels. Many of the phenomena observed in these bubbling vessels correlated with those known to occur in diving. On the basis of our previous studies, which proposed a new model for the formation of arterial bubbles, we now suggest the biophysical model presented herein. There are two phases of bubble expansion after decompression. The first is an extended initiation phase, during which nanobubbles are transformed into gas micronuclei and begin to expand. The second, shorter phase is one of simple diffusion‐driven growth, the inert gas tension in the blood remaining almost constant during bubble expansion. Detachment of the bubble occurs when its buoyancy exceeds the intermembrane force. Three mechanisms underlying the appearance of arterial bubbles should be considered: patent foramen ovale, intrapulmonary arteriovenous anastomoses, and the evolution of bubbles in the distal arteries with preference for the spinal cord. Other parameters that may be quantified include age, acclimation, distribution of bubble volume, AHS, individual sensitivity, and frequency of bubble formation. We believe that the vascular bubble model we propose adheres more closely to proven physiological processes. Its predictability may therefore be higher than other models, with appropriate adjustments for decompression illness (DCI) data.

Blood flow volume quantification of cerebral ischemia: comparison of three noninvasive imaging techniques of carotid and vertebral arteries

OBJECTIVE

Determination of blood flow volume is useful in assessing ischemic cerebrovascular disease. We compared the blood flow volume measurement of three noninvasive imaging techniques, namely color velocity imaging quantification, spectral Doppler imaging quantification, and MR phase-contrast flow quantification, to see how well the flow values determined by each technique agreed with one another.

SUBJECTS AND METHODS

Flow volume quantification was tested experimentally using a flow simulator and by the three techniques in the vertebral and internal carotid arteries of 40 patients with histories of cerebral ischemia. In the flow simulation study, the flow values in each technique were compared with the phantom flow by the Wilcoxon's signed rank test. In the patient study, the flow values between each paired technique were compared by paired t test. The significance level was taken at p less than 0.05.

RESULTS

Flow volumes were measured by color velocity imaging quantification. MR phase-contrast flow quantification agreed with the phantom flow simulation within the tested range, and spectral Doppler imaging quantification values were significantly overestimated. In patients, a large variation of the blood flow volume was obtained between each technique (p < 0.05). Among them, spectral Doppler imaging quantification showed the highest flow values in the vessels (internal carotid arteries, 312.6 mL/min; vertebral arteries, 112.0 mL/min), followed by color velocity imaging quantification (internal carotid arteries, 216.8 mL/min; vertebral arteries, 58.1 mL/min) and MR phase-contrast flow quantification (internal carotid arteries, 169.1 mL/min; vertebral arteries, 66.5 mL/min).

CONCLUSION

Blood flow volume measurements determined by the three noninvasive imaging techniques on the same vessel can differ widely, and spectral Doppler imaging quantification consistently overestimated the flow volume. It is, therefore, essential that the same technique, preferably color velocity imaging quantification or MR phase-contrast flow quantification, be used for clinical follow-up investigations in the future.

Anthropomorphic carotid bifurcation phantom for MRI applications

Anthropomorphic carotid bifurcation flow phantoms that incorporate different stenotic geometries within the internal carotid artery have been developed. This technique produces high-fidelity, life-size vascular flow models that are compatible with magnetic resonance techniques. The models, in conjunction with a computer-controlled flow pump, address the need for a complex vascular geometry that can be used to verify magnetic resonance angiography (MRA) techniques that quantify stenosis severity and blood flow. Stenotic geometries, with up to 80% diameter reduction, have been fabricated in two different phantom materials. Plastic phantoms provide a durable, rigid geometry where the absolute dimensions of the model are well known. Agar gel phantoms provide tissue-like signal (T1, T2) up to the lumen boundary and are also compatible with ultrasound techniques. In this paper the technique to produce vascular flow phantoms is outlined and the compatibility of these phantoms with MRA techniques is demonstrated. J. Magn. Reson. Imaging 1999;10:533-544.

MR flow quantification using RACE: clinical application to the carotid arteries

Real time MR flow quantification was performed with real time acquisition and evaluation of motion (RACE) in a rigid phantom under steady flow conditions and in the common carotid arteries of 43 subjects aged 24-78 years. Hemodynamic information included the intraluminal velocity distribution during the complete cardiac cycle, the distensibility of the arterial wall, and age-dependent changes of the flow curves. Systolic peak velocities of 51 +/- 33 cm/s and time-averaged volume flow rates of 4.3 +/- 2.0 ml/s were measured in healthy subjects. Flow rates below 3.0 ml/s and the observation of abnormal flow patterns indicated stenoses greater than 70% in the region of the bifurcation (sensitivity: 83.3%; specificity: 93.7%; accuracy: 71.4%). Improvements may be achieved from a combination with MR angiography, providing both functional and morphologic vascular information noninvasively within one observer-independent examination. MR imaging, therefore, has a strong potential for the diagnosis of critical stenoses in symptomatic patients.

Three-vessel study of cerebral blood flow using phase-contrast magnetic resonance imaging: effect of physical characteristics

The development of phase-contrast magnetic resonance imaging (P-C MRI) provides a noninvasive method for measurement of volumetric blood flow (VFR). We performed P-C MRI to study the effects of physical characteristics on cerebral blood flow. VFR of the left and right internal carotid arteries and basilar artery were measured using P-C MRI and total cerebral blood flow (tCBF) was calculated by summing up the VFR values in the three vessels. Moreover, we investigated the changes in these blood flows as influenced by age, head size, height, weight, body surface area, and handedness. The blood flows were 142 +/- 58 ml/min (mean +/- standard deviation) in the basilar artery; and 229 +/- 86 ml/min in the left, and 223 +/- 58 ml/min in the right internal carotid artery; and tCBF was 617 +/- 128 ml/min. Significant increases were observed in head size-related change of VFR in the basilar artery (p = .028) and height-related change of tCBF (p = .045). The other characteristics did not significantly influence any VFR. The results suggest that head size and height may reflect CBF, and that these effects should be considered when changes of CBF are diagnosed. Phase-contrast MRI is useful for a noninvasive and rapid analysis of cerebral VFR and has potential for clinical use.

A theory to correct the systematic error caused by the imperfectly matched beam width to vessel diameter ratio on volumetric flow measurements using ultrasound techniques

When a multigate procedure is used to measure volumetric flow in vessels, in addition to the flow rate result obtained from the conventional velocity profile method, a second result from an "average velocity profile method" can be obtained simultaneously. The latter method obtains the flow rate from the product of the average velocity across the profile and the cross-sectional area of the vessel. A theoretical model has been used to study the effect of the beam width to vessel diameter ratio (BWR) on these two results, as well as a third flow rate result obtained from the uniform insonation method. A theory has been established to correct the systematic error caused by the imperfectly matched BWR associated with each method. It uses a correction factor and the difference between the results from the average velocity profile method and the velocity profile method to compensate for the systematic error. The relationship between an optimal correction factor and the BWR under different flow conditions has been studied. The results using the correction theory in this model show that if the estimated BWR is within +/- 0.1 from the actual BWR value, the theoretical error in volumetric flow estimation can be limited to within 6.5% for the entire range of BWR.

Rapid volume flow rate estimation using transverse colour Doppler imaging

A system is described in which the volume flow rate of blood in a vessel is determined using transverse colour Doppler ultrasound imaging. The system measures rapidly the two-dimensional velocity profile of blood flowing through a vessel. By integration of the measured velocity profiles the volume flow rate of blood in the vessel is obtained. The Doppler angle is obtained from the included angle between two imaging planes, and their respective average measured flows. This technique yields instantaneous and average flow rate in real time, and permits long flow recordings to be made and stored digitally. The error is less than 5% over a 8:1 flow rate range.

Carotid and vertebral artery blood flow in left- and right-handed healthy subjects measured with MR velocity mapping

The goal of the study was to establish normal carotid artery flow rates in left-handed and right-handed individuals as a standard against which patients with carotid artery disease could be compared. Antegrade and retrograde flow were measured in the ascending aorta, in the right and left common, internal, and external carotid arteries, and in the vertebral arteries of 12 healthy subjects. Five subjects were right-handed, five left-handed, and two ambidextrous. Measured flow rates were as follows: common carotid arteries, 360-557 mL/min (mean [+/- standard deviation], 465 mL/min +/- 52); internal carotid arteries, 132-367 mL/min (mean, 265 mL/min +/- 60); external carotid arteries, 113-309 mL/min (mean, 186 mL/min +/- 51); vertebral arteries from 133-308 mL/min (mean, 244 mL/min +/- 43); and cerebral circulation, 546-931 mL/min (mean, 774 mL/min +/- 134). All right-handed subjects had higher flow rates in the left internal carotid artery than in the right, and all left-handed subjects had higher flow rates in the right internal carotid artery (P = .007). There were no significant differences in left and right common carotid artery flow rates between left- and right-handed subjects. The standard deviation of a single measurement was 5%. The flow rates were similar to those obtained previously with other techniques and could be used as a normal standard.