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

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.

Blood Flow Volume Measurement in Cervical and Intracranial Arteries using Quantitative Magnetic Resonance Angiography and Duplex Sonography (Bocaccia) - A Prospective Observational Study

PURPOSE

 Cerebral blood flow volume is an important factor for the accurate diagnosis of neurovascular diseases and treatment indication. This study aims to assess correlations of blood flow volume measurements in cervical and intracranial arteries between duplex sonography and quantitative magnetic resonance angiography (qMRA).

MATERIALS AND METHODS

 Consecutive patients with suspicion of cerebral vascular pathology underwent qMRA and duplex sonography of cervical and intracranial arteries with measurement of blood flow volume in bilateral common (CCA), internal (ICA) and external carotid arteries, vertebral and basilar arteries, middle, anterior, posterior cerebral and posterior communicating arteries using 2 different ultrasound machines. Ten patients underwent all examinations twice. Correlations between blood flow volume measurements were evaluated using Spearman's correlation coefficient and inter-class correlation coefficient (ICC).

RESULTS

 In total, 21 subjects (15 males, mean age: 56.3 ± 6.2 years) were included in the study. Duplex sonography inter-investigator correlation was excellent (ICC = 0.972, p < 0.0001) as well as intra-investigator correlations of both qMRA and duplex sonography (ICC ˃ 0.990, p < 0.0001). Mostly high correlations were recorded between qMRA and duplex sonography in particular cervical arteries but only low to moderate correlations were obtained for intracranial arteries. The mean differences between blood flow volume measurements were 10.9 ± 8.1 % in the CCA and its branches when using qMRA and 15.0 ± 11.9 % when using duplex sonography, 13.5 ± 11.8 %/35.4 ± 34.2 % in the ICA siphon and its branches when using qMRA/duplex sonography, and 24.1 ± 19.7 %/44.9 ± 44.0 % in both vertebral arteries and the basilar artery when using qMRA/duplex sonography.

CONCLUSION

 Duplex sonography as well as qMRA allow for highly reproducible measurement of blood flow volume in cervical and intracranial arteries in routine clinical practice.

[Local cerebral hemodynamics following STA-MCA bypass in patients with symptomatic carotid occlusions]

PURPOSE

To assess changes in local hemodynamic parameters in patients with symptomatic ICA occlusions and moyamoya disease after placement of extracranial-intracranial bypass (EC-IC bypass).

MATERIAL AND METHODS

The study included 112 patients who underwent surgical treatment at the National Scientific and Practical Center for Neurosurgery in the period between 1999 and 2015. Of these, 105 patients had ICA occlusions, and 7 patients had moyamoya disease. During the main stage of EC-IC bypass placement, all patients were monitored for local hemodynamic parameters using intraoperative contact Doppler ultrasonography - 89 (72%) patients (72%) and flowmetry - 56 (50%)). In 33 (29%) cases, both techniques were used. Forty two patients underwent preoperative SCT perfusion to assess the degree of perfusion deficit. Grade 1 cerebrovascular insufficiency (acute oligemia) was detected in 6 patients; grade 2 perfusion deficit (persistent oligemia) was found in 25 patients; grade 3 perfusion deficit (chronic oligemia) was present in 11 patients. Measurements were performed before bypass placement: the blood flow direction and hemodynamic parameters in the cortical arteries were evaluated; and after bypass placement: blood flow values and directions in the cortical artery, proximal and distal to the bypass area, were assessed.

RESULTS

A total of 112 EC-IC bypasses were placed without perioperative complications and deaths. Bypass functioning was confirmed in 108 (96.3%) cases; bypass thrombosis occurred in 4 (3.7%) cases. The distal blood flow direction was observed in patients with ICA occlusions (105 patients) in all cases before EC-IC bypass placement. Patients with moyamoya disease had more often the proximal blood flow direction - 5 (71%) out of 7 cases. The cerebral blood flow parameters obtained in this study differed significantly, depending on the baseline degree of perfusion deficit. The blood flow rate was minimal in patients with grade 1 cerebrovascular insufficiency. After revascularization, local hemodynamics in the cortical arteries was significantly dependent on the ability of EC-IC bypass to reverse blood flow in the proximal acceptor artery. A change in the blood flow direction was observed in 86 (77%) cases. The mean volumetric blood flow in EC-IC bypass was 34.2±5.7 mL/min.

CONCLUSION

The knowledge of baseline hemodynamic parameters and their changes after revascularization plays an important role in choosing the correct surgical technique, further bypass functioning, and, as a result, improvement of the clinical outcome after surgery.

Headstand (Sirshasana) Does Not Increase the Blood Flow to the Brain

Objectives: Most yoga practitioners believe that headstand (Sirshasana) results in increased cerebral perfusion. This, however, is not consistent with autoregulation of the cerebral blood flow. The intent of this study was to demonstrate the effect of Sirshasana on the blood flow to the brain through ultrasound examination of the internal carotid artery (ICA). Design, location, and subjects: The ICA blood flow was measured with pulsed Doppler in 20 men and women aged 10 to 59 years (median 43) while performing the headstand (Sirshasana). Seventeen subjects were studied in 2018 in Spain at the altitude of 2,000 m, whereas the other three females were studied at sea level. Results: Although the diameter of the artery under examination during the headstand remained almost unchanged, the decrease in peak flow velocities in systole and diastole caused a significant decrease in arterial blood flow to the brain, followed by return to baseline values immediately after the antiorthostatic postural effect, likely due to the expected consequences of the cerebral blood flow autoregulation of the cerebral blood supply as well as the intracranial pressure. Conclusions: Contrary to popular belief, Sirshasana does not increase blood flow to the brain through the ICA, but results in predictable reduction in cerebral blood delivery in compliance with known mechanisms of autoregulation of cerebral blood flow. Moreover, increased ICA blood flow while performing the headstand is likely to be a contraindication to this exercise.

Effect of cervical manipulation on vertebral artery and cerebral haemodynamics in patients with chronic neck pain: a crossover randomised controlled trial

OBJECTIVE

It is hypothesised that cervical manipulation may increase the risk of cerebrovascular accidents. We aimed to determine whether cervical spine manipulation is associated with changes in vertebral artery and cerebrovascular haemodynamics measured with MRI compared with neutral neck position and maximum neck rotation in patients with chronic neck pain.

SETTING

The Imaging Research Centre at St. Joseph's Hospital in Hamilton, Ontario, Canada.

PARTICIPANTS

Twenty patients were included. The mean age was 32 years (SD ±12.5), mean neck pain duration was 5.3 years (SD ±5.7) and mean neck disability index score was 13/50 (SD ±6.4).

INTERVENTIONS

Following baseline measurement of cerebrovascular haemodynamics, we randomised participants to: (1) maximal neck rotation followed by cervical manipulation or (2) cervical manipulation followed by maximal neck rotation. The primary outcome, vertebral arteries and cerebral haemodynamics, was measured after each intervention and was obtained by measuring three-dimensional T1-weighted high-resolution anatomical images, arterial spin labelling and phase-contrast flow encoded MRI. Our secondary outcome was functional connectivity within the default mode network measured with resting state functional MRI.

RESULTS

Compared with neutral neck position, we found a significant change in contralateral blood flow following maximal neck rotation. There was also a significant change in contralateral vertebral artery blood velocity following maximal neck rotation and cervical manipulation. We found no significant changes within the cerebral haemodynamics following cervical manipulation or maximal neck rotation. However, we observed significant increases in functional connectivity in the posterior cerebrum and cerebellum (resting state MRI) after manipulation and maximum rotation.

CONCLUSION

Our results are in accordance with previous work, which has shown a decrease in blood flow and velocity in the contralateral vertebral artery with head rotation. This may explain why we also observed a decrease in blood velocity with manipulation because it involves neck rotation. Our work is the first to show that cervical manipulation does not result in brain perfusion changes compared with a neutral neck position or maximal neck rotation. The changes observed were found to not be clinically meaningful and suggests that cervical manipulation may not increase the risk of cerebrovascular events through a haemodynamic mechanism.

TRIAL REGISTRATION NUMBER

NCT02667821.

Local Cerebral Hemodynamics after Superficial Temporal Artery-Middle Cerebral Artery Bypass in Patients with Symptomatic Carotid Occlusions

Context

Physiological insights into blood flow alterations in cortical vessels after superficial temporal artery-middle cerebral artery (STA-MCA) bypass surgery are important for the prognosis of bypass sustainability and hemodynamic patency.

Aims

This study aims to assess the impact of STA-MCA bypass on local hemodynamics for patients with symptomatic carotid occlusions and Moyamoya disease.

Settings and Design

This article presents a prospective nonrandomized study of intraoperative blood flow measurements in cortical branches of MCA and donor vessel before and after cerebral revascularization.

Materials and Methods

Evaluation of local hemodynamic parameters was established for 112 patients with symptomatic carotid occlusive disease and cerebrovascular insufficiency during STA-MCA bypass surgery. We used intraoperative Doppler ultrasonography (89 patients - 72%), flowmetry (56 cases - 50%), and in 33 cases both methods. For physical justification of observed facts, we performed computational simulation with OpenFOAM CFD framework using Navier-Stokes nonstationary hemodynamic model.

Statistical Analysis Used

All calculations were performed with IBM SPSS Statistics version 10.0 software. We used parametric (Z-test and Student's t-test) and nonparametric models (Wilcoxon, Mann-Whitney). For categorical values, we used Fisher's exact test.

Results

Local cerebral hemodynamics after revascularization surgery significantly depended on initial perfusion deficit and the ability of bypass to reverse the blood flow in proximal parts of cortical artery (86 cases, 77%). Mechanism of cortical blood flow alteration was related to donor vessel cut flow value and potential consumption threshold of acceptor artery.

Conclusions

Knowledge of hemodynamic principles of flow redistribution after STA-MCA bypass is important to improve bypass stainability and leads to better revascularization results.

Measurement of cerebral blood flow using phase contrast magnetic resonance imaging and duplex ultrasonography

Phase contrast magnetic resonance imaging (PC-MRI) and color-coded duplex ultrasonography (CDUS) are commonly used for measuring cerebral blood flow in the internal carotid (ICA) and vertebral arteries. However, agreement between the two methods has been controversial. Recent development of high spatial and temporal resolution blood vessel wall edge-detection and wall-tracking methods with CDUS increased the accuracy and reliability of blood vessel diameter, hence cerebral blood flow measurement. The aim of this study was to compare the improved CDUS method with 3 T PC-MRI for cerebral blood flow measurements. We found that cerebral blood flow velocity measured in the ICA was lower using PC-MRI than CDUS (left ICA: PC-MRI, 18.0 ± 4.2 vs. CDUS, 25.6 ± 8.6 cm/s; right ICA: PC-MRI, 18.5 ± 4.8 vs. CDUS, 26.6 ± 6.7 cm/s, both p < 0.01). However, ICA diameters measured using PC-MRI were larger (left ICA: PC-MRI, 4.7 ± 0.50 vs. CDUS, 4.1 ± 0.46 mm; right ICA: PC-MRI, 4.5 ± 0.49 vs. CDUS, 4.0 ± 0.45 mm, both p < 0.01). Cerebral blood flow velocity measured in the left vertebral artery with PC-MRI was also lower than CDUS, but no differences in vertebral artery diameter were observed between the methods. Dynamic changes and/or intrinsic physiological fluctuations may have caused these differences in vessel diameter and velocity measurements between the methods. However, estimation of volumetric cerebral blood flow was similar and correlated between the methods despite the presence of large individual differences. These findings support the use of CDUS for cerebral blood flow measurements in the ICA and vertebral artery.

Compensatory patterns of collateral flow in stroke patients with unilateral and bilateral carotid stenosis

Background

Collateral pathways are important in maintaining adequate cerebral blood flow in patients with carotid stenosis. We aimed to evaluate the hemodynamic patterns in relation to carotid stenosis in acute stroke patients.

Methods

Consecutive 586 stroke patients in a hospital based cohort were included in the present study. Carotid duplex was performed to identify patients with absolute minimal diameter reductions of 50 % or greater in their internal carotid arteries (ICAs). Color velocity imaging quantification ultrasound (CVIQ) was used to measure extracranial arterial blood flow volume (BFV) in bilateral common carotid arteries (CCAs) and bilateral vertebral arteries (VAs). The absolute values of BFV and the ratios were compared between patients with and without ICA stenosis.

Results

Among 586 acute ischemic stroke patients (mean age: 67.5 ± 12.4y), ICA stenosis was detected in 112 patients (19.1 %), including unilateral ICA stenosis in 81 patients (13.8 %) and bilateral ICA stenosis in 31 patients (5.3 %). Among patients with unilateral ICA stenosis, the BFV in contralateral CCA was significantly higher than that in ipsilateral CCA (325.5 ± 99.8 mL/min vs. 242.2 ± 112.2 mL/min, P < 0.001). Among patients with bilateral ICA stenosis, the sum of BFV in bilateral VAs accounted for 22 % of the whole cerebral blood flow, which was significantly higher than that in those without ICA stenosis (14.8 %, P < 0.001) or with unilateral ICA stenosis (16.9 %, P = 0.007).

Conclusions

In patients with unilateral carotid stenosis, contralateral carotid blood flow increases to compensate decreased blood flow, while posterior circulation may compensate for the decreased brain perfusion in those with bilateral carotid stenosis.

Sizes of the transverse foramina correlate with blood flow and dominance of vertebral arteries

BACKGROUND CONTEXT

Knowing the side of the dominant vertebral artery (VA) may be of utmost importance if the VAs are at risk during spine surgery. Determination of the size of VAs is obtained by using Doppler ultrasonography or angiography. Because VA is the main anatomic structure occupying the transverse foramina (TF), it may be assumed that size of TF and blood flow of VAs should be proportional.

PURPOSE

To investigate if there is a correlation between the sizes of TF and the flow of VAs and determine the diagnostic accuracy of measuring TF to predict dominant side of VA. The specific hypothesis was that the larger side of TF corresponds to the side of the dominant VA.

STUDY DESIGN

This is a morphologically based, prospectively designed, single-center study. Thirty patients (14 male, 16 female) who were treated for degenerative spinal pathologies were included. Patients with cervical fractures, occluded VA, prominent degenerative changes affecting TF, deformity, or previous cervical instrumentation were excluded from the study.

OUTCOME MEASURES

In all patients, computed tomography of the cervical spine and Doppler ultrasonography of VAs were obtained for morphometric analysis.

METHODS

Axial computed tomography cuts at the C6 vertebral level were taken. Two measurements were performed for each foramen: its right to left width and its anteroposterior depth. Blood flow volumes of bilateral VAs were measured using color Doppler.

RESULTS

Diameters of TF ranged between 2.2 and 7 mm, and its width was generally slightly larger than the depth. Transverse foramina were always asymmetric, with no right or left side preference. There was a strong correlation between TF diameters and blood flow of VAs. Between TF width and VA blood flow, the Pearson correlation coefficient was 0.59 (p=.001) for right side and 0.72 for left side (p<.0001). The side of the larger TF matched with the side of dominant VA in 28 of 30 cases (93.3%) (p<.0001). The agreement between the dominant VA and the larger side of TF was almost perfect (Kappa=0.087, p<.0001).

CONCLUSIONS

There was strong correlation between TF diameters and VA blood volume. Our results suggest that TF diameter of C6 level can be used to predict the side of the dominant VA reliably.

EXPERIMENTAL ASSESSMENT OF THE IMPACT OF ASYMPTOMATIC GAS EMBOLI ON THE VESSEL WALL

Quantitative evaluation of shear stress in the vessel wall due to the presence of asymptomatic gas emboli is lacking. The goal of this work was to assess the impact of chronic asymptomatic gas emboli on the risk of atherosclerosis through a custom-built cardiovascular flow simulator. Gas bubbles were created by forced air from a syringe pump. The influences of embolism injection rate, pulse rate, and time-averaged flow rate on the wall mean shear stress were investigated at resting and elevated heart rate conditions. The recorded pressure and volumetric flow rate from 24 experimental settings with four repetitions each were used to calculate the mean wall shear stress (MWSS). A directly inverse relationship between gas embolus rate and MWSS in the vessel, particularly at low vascular flow and diminished pulse rates was subsequently found. This study established a positive correlation between gas bubbles in the bloodstream and diminished MWSS, which implied a potential onset of atherosclerosis.

The Effect of the Sitting Upright or ‘Beachchair’ Position on Cerebral Blood Flow during Anaesthesia for Shoulder Surgery

The sitting upright or ‘beachchair’ position is commonly used for shoulder arthroscopic surgery. There is a theoretical concern that anaesthetised patients placed in this posture are at risk of reduced cerebral blood flow (CBF), especially if there is associated hypotension. This study investigated the effect of anaesthetic-induced hypotension on estimated cerebral blood flow in patients placed in the beachchair position for shoulder surgery.

Forty patients were randomised to either sedation (propofol infusion 10 to 20 mg.hour-1, n=20) or general anaesthesia using sub minimum alveolar concentration of sevoflurane (n=20). All patients received an interscalene brachial plexus regional block. Internal carotid artery blood flow was measured using the time averaged velocity of the spectral Doppler waveform, and was then used as an estimate of global CBF. Following a pre-anaesthesia study, measurement of internal carotid artery blood flow was made before and after beachchair positioning, and at five-minute intervals during surgery.

Beachchair positioning during general anaesthesia significantly decreased the mean arterial pressure (34±10 mmHg) compared to sedation (4±2 mmHg, P <0.01), and vasopressor therapy was required more often. However, CBF remained constant in both anaesthetised (P=0.83) and sedated patients (P=0.68) despite beachchair positioning, and the fall in mean arterial pressure in the anaesthetised patients. There was no significant difference in CBF between groups (P=0.91). These findings indicate that in patients in the beachchair position receiving sevoflurane anaesthesia, CBF is maintained when mean arterial pressure is above 70 mmHg, consistent with intact autoregulation.

Womersley number-based estimation of flow rate with Doppler ultrasound: sensitivity analysis and first clinical application

In this paper we continue in investigating the approach we have proposed in a paper recently published, for a reliable estimate of (peak systolic) blood flow rate from velocity Doppler measurements. Basic features of this approach together with some in silico test cases were discussed in that work. Here, we provide more insights of this approach by performing a sensitivity analysis of the formulas relating blood flow rate to velocity. In particular we analyze how our estimates are affected by perturbation or errors in measurements in comparison with a standard method for catheter based estimates based on the assumption of a parabolic velocity profile. A first glance to in vivo clinical applications is given as well.

Non-invasive evaluation of vertebral artery blood flow in cervical spondylosis with and without vertigo and association with degenerative changes

Cervical spondylosis is a common disease that results from degenerative changes of the cervical spine and vertigo may occur in this process. The aim of the present study was to assess the blood flow measurements of the vertebral artery (VA) using color Doppler ultrasonography (CDUS) in patients who have cervical spondylosis with and without vertigo. The study population included 101 patients with vertigo and spondylosis, 66 patients with spondylosis without vertigo, and 62 healthy controls. A bilateral decrease in the VA blood flow velocities were measured in patients with cervical spondylosis. A negative correlation was found between the stage of cervical degenerative changes and the flow velocities in patients with vertigo, while this relationship was not found in patients without vertigo. The CDUS evaluation of the pretransverse and transverse segments of VAs demonstrated significantly reduced flow velocities in patients with spondylosis. The degenerative changes in the cervical spine seem to be related to these velocity changes in the subgroup of patients who are also affected with vertigo. The pretransverse segment of the VA provides valuable measurements as well as transverse segment of the VA, and it can be used as an appropriate segment for CDUS examination in cervical spondylosis and associated vertigo.

Accuracy of volumetric flow rate measurements: an in vitro study using modern ultrasound scanners

OBJECTIVE

Volumetric flow measurement with Doppler ultrasound is useful in assessing blood flow as part of an evaluation of arteriovenous fistula maturity in patients undergoing hemodialysis. In this study, we assessed both accuracy and variability in volumetric flow measurements obtained using modern and commercially available ultrasound systems and an in vitro experimental setup.

METHODS

Volumetric flow measurements using duplex ultrasound were obtained by 3 users operating 5 different systems for randomized flow in the range of 100 to 1000 mL/min. Users performed 3 consecutive measurements at a given flow rate. Data were analyzed using statistical techniques to assess measurement accuracy and variability.

RESULTS

Over the span of flow rates studied, the root mean square error (RMSE) for the 5 ultrasound systems ranged from 38.8 to 79.7, 36.8 to 52.0, 73.0 to 85.3, 26.7 to 44.6, and 43.9 to 93.5 mL/min. Corresponding average RMSE values were 60.3, 42.7, 81.1, 37.2, and 64.4 mL/min, respectively. A linear regression analysis of mean interobserver measurements revealed an excellent correlation for all ultrasound systems (r(2) > 99.1%). Assessment of intraobserver measurements revealed no statistically significant differences for any ultrasound system evaluated (P > .94). Comparison of interobserver measurements indicates no statistically significant differences between any of the 5 systems (P > .14).

CONCLUSIONS

Modern ultrasound systems are reasonably accurate in blood flow measurement in an experimental setup mimicking clinically relevant blood flow ranges in a hemodialysis fistula. Users need adequate training and experience to perform multiple measurements and use appropriate techniques to minimize errors in flow measurement.

Flow volume and cross-sectional area of the extracranial vertebral arteries and its relation to vascular lesions or anatomical variations in the posterior circulation

We examined whether the time-averaged maximum velocity (TAMV), flow volume (FV) or cross-sectional area (CA) in the vertebral arteries (VA) as determined by ultrasonography was related to vascular lesions or variations in the intracranial part of the posterior circulation. Three hundred nine patients without severe stenosis in the carotid circulation (159 males, 150 females, mean age of 69.1 years) underwent both colour duplex ultrasonography and magnetic resonance angiography (MRA) and were thus analyzed. According to the MRA findings, the patients were divided as follows; 22 patients with severe stenosis in the bilateral PCA or VA or basilar artery (V group) and 287 patients without (N group). The N group was then further divided as follows; 144 patients with no (P0 group); 89 with one (P1) and 54 with both posterior communicating arteries (P2) detected on MRA. TAMV, FV and CA were compared among these groups. Both TAMV and FV of V group were significantly lower than those of N group (35.3 vs. 42.6 cm/sec in TAMV, 98.2 vs. 135.3 mL/min in FV, p < 0.001 and 0.0001, respectively). The FVs and CAs in the P0 through P2 groups were all significantly different according to the number of posterior communicating arteries (149.3 vs. 128.0 vs. 109.8 mL/min, 22.5 vs. 20.2 vs. 16.5 mm2, both p < 0.001) while TAMVs in these groups did not differ substantially. The FV in both VAs were thus found to be related to the vascular lesions or variations in the posterior circulation.

Assessment of parathyroid glands in hemodialysis patients by using color Doppler sonography

The aim of this study was to assess the role of color and spectral Doppler ultrasound (CDU) in the evaluation of enlarged parathyroid glands in hemodialysis patients with secondary hyperparathyroidism. Fourteen hemodialysis patients with elevated intact parathyroid hormone (iPTH) levels were evaluated prospectively with CDU. The volume of each observed parathyroid gland and the spectral CDU data (velocities, resistance and pulsatility indices, systolic to diastolic ratio, and flow volume output (FVO)) were noted. The biochemical data (iPTH, calcium, phosphate levels), and CDU results were analyzed with the Spearman correlation test. Two patients were excluded, and 27 enlarged parathyroid glands were observed in 12 patients. The mean total volume of enlarged parathyroid glands per patient was 1.95 cm(3) (0.06-5.5 cm(3)). Arterial supply was demonstrated in 78% (21/27) of enlarged parathyroid glands. Mean total FVO of enlarged glands per patient was 238.5 ml/min (620-0 ml/min) and mean iPTH level was 1,477 pg/ml (643-3,132 pg/ml). The positive correlations of total volume (p = 0.022), iPTH (p = 0.024), and FVO (p = 0.022) were statistically significant. In secondary hyperparathyroidism, total volume of the visualized enlarged parathyroid glands and the total of FVOs per patient are positively correlated with iPTH levels which may help clinical management and follow-up of end-stage renal disease patients.

In vivo validation of a blood vector velocity estimator with MR angiography

Conventional Doppler methods for blood velocity estimation only estimate the velocity component along the ultrasound beam direction. This implies that a Doppler angle under examination close to 90 degrees results in unreliable information about the true blood direction and blood velocity. The novel method transverse oscillation (TO), which combines estimates of the axial and the transverse velocity components in the scan plane, makes it possible to estimate the vector velocity of the blood regardless of the Doppler angle. The present study evaluates the TO method with magnetic resonance phase contrast angiography (MRA) by comparing in vivo measurements of stroke volume. Eleven healthy volunteers were included in this prospective study. From the obtained data sets recorded with the 2 modalities, vector velocity sequences were constructed and stroke volume calculated. Angle of insonation was approximately 90 degrees for TO measurements. The correlation between the stroke volume estimated by TO and MRA was 0.91 (p < 0.01) with the equation for the line of regression: MRA = 1.1.TO-0.4. A Bland-Altman plot was additionally constructed where the mean difference was 0.2 ml with limits of agreement at -1.4 ml and 1.9 ml. The results indicate that reliable vector velocity estimates can be obtained in vivo using the presented angle-independent 2-D vector velocity method. The TO method can be a useful alternative to conventional Doppler systems by avoiding the angle artifact, thus giving quantitative velocity information.

Carotid stenosis assessed with a 4-dimensional semiautomated Doppler system

OBJECTIVE

The purpose of this study was to compare peak systolic velocities (PSVs) and the degree of stenosis obtained with a real-time 3-dimensional (ie, 4-dimensional) Doppler ultrasound scanner (Encore PV; VueSonix Sensors Inc, Wayne, PA) to conventional Doppler ultrasound imaging of the carotid arteries (common [CCA], internal [ICA], and external [ECA]). A secondary goal was to assess Encore volume flow measurements.

METHODS

Seventy patients referred for clinical carotid ultrasound participated in this pilot study. Peak systolic velocities of the CCA, ECA, and ICA were obtained bilaterally. The degree of stenosis in the ICA was calculated based on the ICA PSV and ICA/CCA PSV ratio. The Encore detects all 3-dimensional blood flow velocity vectors within 10-s longitudinal volumes of the ICA, ECA, and CCA. On the Encore, a reader determined the centerline of the vessels. The PSV and volume flow were then automatically calculated. The flow measurement error was obtained by comparing the CCA flow to the ICA and ECA flow. Data were compared using linear regression, intraclass correlation coefficients (ICCs), and Bland-Altman analysis.

RESULTS

Due to technical difficulties, only 59 patients (323 vessel segments) were available for analysis. There was good agreement between methods for assessing the degree of stenosis based on the ICA PSV (ICC = 0.83; P < .0001) and, to a lesser degree, on the ICA/CCA PSV ratio (ICC = 0.65; P < .0001). Peak systolic velocity measurements obtained with conventional ultrasound and the Encore correlated in all vessels (r >or= 0.32; P < .002), and Bland-Altman analysis showed reasonable variations. The Encore mean volume flow error +/- SD was -4.1% +/- 66.4% and was not biased (P = .57).

CONCLUSIONS

A new semiautomated 4-dimensional Doppler device is comparable to conventional Doppler ultrasound for assessment of carotid stenosis.

Preliminary Findings of External Counterpulsation for Ischemic Stroke Patient With Large Artery Occlusive Disease

Background and Purpose— We aimed to investigate the feasibility and therapeutic effect of external counterpulsation (ECP) in ischemic stroke.

Methods— The trial was a randomized, crossover, assessment-blinded, proof-of-concept trial. ECP treatment consisted of 35 daily 1-hour sessions. Patients were randomized to either early (ECP weeks 1 to 7 and no ECP weeks 8 to 14) or late group (no ECP weeks 1 to 7 and ECP weeks 8 to 14). Primary outcomes were an overall change in National Institutes of Health Stroke Scale (NIHSS) and cerebral blood flow estimated by color velocity imaging quantification. Secondary outcomes were change in NIHSS, color velocity imaging quantification, favorable functional outcome (modified Rankin scale, 0 to 2), and stroke recurrence at weeks 7 and 14, respectively.

Results— Fifty patients were recruited. At week 7, there was a significant change in NIHSS (early 3.5 vs late 1.9; P =0.042). After adjusting for treatment sequence, ECP was associated with a favorable trend of change in NIHSS of 2.1 vs 1.3 for non-ECP ( P =0.061). Changes of color velocity imaging quantification were not significant but tended to increase with ECP. At week 14, a favorable functional outcome was found in 100% of early group patients compared to 76% in the late group ( P =0.022).

Conclusion— ECP is feasible for ischemic stroke patients with larger artery disease.

Changing concepts of cerebrospinal fluid hydrodynamics: role of phase-contrast magnetic resonance imaging and implications for cerebral microvascular disease

Phase-contrast magnetic resonance imaging (PC-MRI) or flow-sensitive MRI can be used to noninvasively measure intracranial vascular and CSF flow. Monro-Kellie homeostasis is the complex compensatory mechanism for the increase in intracranial blood volume during systole. Through PC-MRI techniques, our understanding of Monro-Kellie homeostasis and the associated intracranial hydrodynamics has greatly improved. Failure of this homeostatic mechanism has been implicated in a wide range of cerebral disorders, including vascular and Alzheimer's dementia, late-onset depression, benign and secondary intracranial hypertension, communicating and normal pressure hydrocephalus, and age-related white matter changes. The most common mode of homeostatic failure is due to vascular disease with decreased cerebral arterial compliance. This has wide-reaching implications in the investigation of patients with cerebral vascular disease. Here we discuss the role of PC-MRI in the study of cerebral hydrodynamics and the current understanding of Monro-Kellie homeostasis in both healthy and disease states. Quantitative assessment of the changes in this homeostatic mechanism using PC-MRI has important implications in the development of biomarkers of vascular involvement in disease with application in diagnosis, treatment planning, phenotype identification, and outcome assessment in clinical trials.

Total cerebral blood flow estimated by color velocity imaging quantification ultrasound: a predictor for recurrent stroke?

Although the Virchow's triad on thrombosis includes reduced blood flow as a factor, there has been relatively little data on the importance of total cerebral blood flow on the risk of subsequent stroke. In the current study, we investigate whether total cerebral blood flow helps predict stroke recurrence. Extracranial arterial blood flow volume estimated by color velocity imaging quantification ultrasound (CVIQ) is an index of cerebral blood flow measurement. We performed a cohort study of 210 consecutive acute stroke patients. Patients were studied with transcranial Doppler and duplex ultrasound for intra- and extracranial large artery disease within 3 days of symptom onset. The association between the risk of recurrent stroke and CVIQ was analyzed with Cox proportional hazards model. Thirty-nine patients (17.7%) developed an ischemic stroke during a mean follow-up of 47.5 months. The mean extracranial blood flow volume was significantly lower for patients who had a recurrent stroke than those without (594.4+/-130.3 versus 683.8+/-176.9 mL/min; P=0.003). In a Cox proportional hazards model adjusting for potential confounding variables, extracranial blood flow volume (hazard ratio (HR) for lowest tertile, 4.1; 95% confidence interval (CI), 1.5 to 11.0) along with male sex (HR, 2.5; 95% CI, 1.3 to 5.1), diabetes (HR, 2.5; 95% CI, 1.2 to 5.0) and large artery stenosis (HR, 2.2; 95% CI, 1.1 to 4.4) were independent predictors for stroke recurrence. Our data indicated that patient with low amount of blood flow to the brain is at risk of recurrent stroke.

Validating volume flow measurements from a novel semiautomated four-dimensional Doppler ultrasound scanner

RATIONALE AND OBJECTIVES

Accurate measurement of blood volume flow (in ml/min) is an important clinical goal. This project compared in vitro and in vivo volume flow measurements obtained with a novel, real-time three-dimensional (i.e., four-dimensional) ultrasound scanner (Encore PV; Vuesonix Sensors, Wayne, PA) with those from an invasive transit time flowmeter.

MATERIALS AND METHODS

A flow pump was used to generate pulsatile flow rates from 60 to 600 ml/min. The Encore detected absolute blood velocity vectors within a volume. The scanner determined the centerline of the vessel and volume flow was then automatically calculated. Results were compared with those of an invasive technique for volumetric blood flow measurements utilizing a transit-time flowmeter (TS420; Transonic Systems Inc., Ithaca, NY). In vivo, 10 second datasets of the volume flow in the distal aorta of six rabbits were obtained simultaneously with the Encore PV and the flowmeter. Data were compared using linear regression and Bland-Altman analysis (due to the lack of independence).

RESULTS

In vitro, Encore and flowmeter measurements both matched the flow pump (r2 > 0.99; P < .0001) with mean errors of -11.8% and -0.3%, respectively. Marked underestimation of the true flow rates was encountered with the Encore at the lowest pump setting. In vivo mean volume flows between 10.6 and 79.3 ml/min were measured. Mean and maximum volume flows obtained with the two techniques correlated significantly (P < .0001) with r2 values of 0.86 and 0.62, respectively. The corresponding root-mean-square errors were 6.9% for mean flow and 61.2% for maximum volume flow measurements.

CONCLUSION

A new semiautomated four-dimensional Doppler device has been tested in vitro and in vivo. Mean volume flow measurements with this unit are comparable to those of an invasive flowmeter.

Arterial blood flow to the brain in patients with vascular disease: the SMART Study

PURPOSE

To retrospectively investigate which characteristics are related to total arterial blood flow to the brain in patients with symptomatic vascular disease.

MATERIALS AND METHODS

The study was approved by the ethics committee of the authors' institution, and written informed consent was obtained. The total volume flow rate (tVFR) values in the internal carotid arteries and the basilar artery in 636 patients (536 men, 100 women; mean age, 58 years) with symptomatic vascular disease were measured with two-dimensional phase-contrast magnetic resonance (MR) angiography. Reference tVFR values in the general population were obtained from previous research involving 158 subjects (73 men, 85 women; mean age, 60 years).

RESULTS

A higher tVFR was found in patients with symptomatic vascular disease, but this association was statistically significant in only those patients in the 7th decade of life. The mean tVFR decreased with increasing age (-3.4 mL/min per year; 95% confidence interval [CI]: -4.3, -2.5). Diabetes (-27.6 mL/min; 95% CI: -52.6, -2.6) and increasing body mass index (BMI) (-2.8 mL/min per BMI unit; 95% CI: -5.3, -0.2) were associated with lower tVFR. Patients with vascular disease in a cerebral location had lower tVFR values (-39.7 mL/min; 95% CI: -65.1, -14.3) than did patients with symptomatic vascular disease elsewhere in the vascular tree.

CONCLUSION

Patients with symptomatic vascular disease had slightly higher arterial blood flow to the brain compared with the general population. The tVFR decreased with increasing age and increasing BMI, and patients with diabetes had lower tVFR values than did those without diabetes. Patients with vascular disease in a cerebral location had lower tVFR values than did those with symptomatic vascular disease at other arterial sites.

An improved spectral width Doppler method for estimating Doppler angles in flows with existence of velocity gradients

Doppler angle (i.e., beam-to-flow angle) is an important parameter for quantitative flow measurements. With known Doppler angles, volumetric flows can be obtained by the mean flow velocity times the cross-section area of the vessel. The differences or changes between prestenotic and poststenotic volumetric flows have been quantified as an indicator for assessing the clinical severity of the stenosis. Therefore, several research groups have dedicated themselves to developing user-independent methods to determine automatically the Doppler angle. Nevertheless, most of these methods were developed for narrow ultrasound beam measurements. For small vessels, where the beam width is a significant fraction of the diameter of the vessel, the effect of velocity gradients plays an important role and should not be ignored in the Doppler angle estimations. Accordingly, this paper is concerned with a method for improving the estimation of Doppler angles from spectral width Doppler (SWD) method, but correcting for velocity-gradient broadening that may arise when the beam has a nonzero width. In our method, Doppler angles were firstly calculated by SWD and then were corrected by an artificial neural network (ANN) method to neutralize the contribution of velocity gradient broadening (VGB). This SWD and ANN conjoint method has been successfully applied to estimate Doppler angles from 50 degrees to 80 degrees for constant flows in 10 mm, 4 mm and 1 mm diameter tubes, whose mean flow velocities were 15.3, 19.9 and 25.5 cm/s, respectively, and the achieved mean absolute errors of the estimated Doppler angles were 1.46 degrees , 1.01 degrees and 1.3 degrees.

Magnetic Resonance Angiography of Cerebral Arteries After Neonatal Venoarterial and Venovenous Extracorporeal Membrane Oxygenation

Background and Purpose— In newborns with severe respiratory failure, extracorporeal membrane oxygenation (ECMO) has been proven to improve survival. With venoarterial ECMO, the right common carotid artery is ligated, whereas with venovenous ECMO, this carotid artery remains intact. The authors present the magnetic resonance angiography (MRA) evaluation of cerebral hemodynamics in a case of venoarterial and a case of venovenous ECMO.

Methods— With 2D phase-contrast MRA flow volume (mL/min), measurements are obtained of the brain feeding arteries and draining veins. Time-of-flight and flow-directional MRA are used to demonstrate the anatomy and flow patterns at the level of the circle of Willis.

Results– A total volume flow of 63 mL/min at the skull base and collateral flow via the anterior circle of Willis were measured in the infant after venoarterial ECMO, and a total volume flow of 86 mL/min and a fetal type configuration of the circle of Willis were observed in the infant after venovenous ECMO.

Conclusion— MRA is a useful technique to quantify cerebral blood flow in neonates after venoarterial or venovenous ECMO and could be used to select neonates with insufficient collateral compensation after venoarterial ECMO, requiring revascularization surgery.

Potential Value of Poststroke Extracranial Arterial Blood Flow Volume in the Prediction of Stroke Functional Outcome

BACKGROUND AND PURPOSE

Cerebral vasoreactivity and collateral circulation are important protective mechanisms against cerebral ischemia. Previous studies suggest that the efficiency of these mechanisms can be reflected by extracranial arterial blood flow volume. Brain damage leading to neurological impairments can influence patients' functional recovery after stroke. This study attempted to explore the potential value of post stroke extracranial arterial blood flow volume in the prediction of stroke patients' functional outcome.

METHODS

We prospectively studied 362 consecutive patients who were hospitalized for recent acute strokes. All patients underwent extracranial arterial blood flow volume measurement of the carotid and vertebral arteries by color velocity imaging quantification within 3 days after admission. Their functional recovery was assessed 6 months after stroke. The effect of post stroke extracranial arterial blood flow volume on patients' functional outcome was tested by multivariate ordinal regression after controlling for other independent variables. Significance was at p<0.05.

RESULTS

Post stroke extracranial arterial blood flow volume together with age, pre-stroke modified Rankin scale, the National Institutes of Health Stroke Scale and diabetes mellitus had significant effects on the patients' 6-month functional outcome as measured by the modified Rankin scale after controlling for other independent variables (p<0.05).

CONCLUSIONS

Post stroke extracranial arterial blood flow volume is an independent outcome predictor. The graded predictive power of this parameter is potentially more superior than other outcome predictors by allowing classification of stroke outcome according to the degree of severity. A large prospective study is thus warranted to investigate its clinical value in the management of stroke patients.

Comparison of vertebral artery velocity and flow volume measurements for diagnosis of vertebrobasilar insufficiency using color duplex sonography

INTRODUCTION

The aim of this study was to compare the measurements of vertebral artery (VA) systolic flow velocity and flow volume for diagnosis of vertebrobasilar insufficiency (VBI).

MATERIAL AND METHODS

We examined 96 patients who were referred for evaluation of VBI. Net vertebral artery flow volume and mean systolic flow velocity were determined by using color duplex sonography. We had grouped the patients into three according to VA flow volume: group 1 was consisted of patients with severely damped VA flow volume (lower than 120 mL/min), group 2 was consisted of patients with moderately damped VA flow volume (120-200 mL/min), group 3 was consisted of patients with normal VA flow volume (>200 mL/min). The mean systolic flow velocities in each group were compared by one-way ANOVA.

RESULTS

Mean VA systolic flow velocities of groups 1, 2 and 3 were 32 +/- 12, 42 +/- 10 and 46 +/- 8 cm/s, respectively. Mean VA systolic flow velocity in group 1 was significantly lower than that of group 2 (P = 0.001). However, there were no significant differences between VA systolic flow velocities in groups 2 and 3 (P = 0.2).

CONCLUSIONS

According to our findings, measurement of volume in addition to velocity is more valuable in detection of moderately damped VA flow volumes in diagnosis of VBI.

Monitoring of Cerebral Blood Flow and Metabolism in Traumatic Brain Injury

The aim of the present study was to investigate the course of cerebral blood flow (CBF) and metabolism in traumatic brain injury (TBI) patients and to specifically characterize the changes in lactate and glucose indices in the acute post-traumatic period with regard to neurological condition and functional outcome. For this purpose, 55 consecutive TBI patients (mean age 37 +/- 17 years, mean GCS 6.8 +/- 3.2) were prospectively and daily evaluated. Global CBF, cerebral metabolic rates of oxygen (CMRO2), glucose (CMRGlc), and lactate (CMRLct) were calculated using arterial jugular differences. In all patients, CBF was moderately decreased during the first 24 h in comparison with normal subjects although this relative oligemia was more pronounced in patients with poor outcome (p = 0.0007). Both CMRO2 and CMRGlc were significantly depressed and correlated to outcome (p < 0.0001, p = 0.0088). CMRLct analysis revealed positive values (lactate uptake) during the first 48 h, especially in patients with favorable outcome. Both CMRO2 and CMRLct correlated with GCS (p = 0.0001, p = 0.0205). CMRLct levels showed an opposite correlation with CBF in patients with favorable and poor outcome. In the former group, correlation analysis exhibited a negative slope with evidence for increasing lactate uptake associated with lower CBF values (r = -0.1940, p = 0.0242). On the contrary, in patients with adverse outcome, CMRLct values demonstrated a weak though opposite correlation with CBF (r = 0.0942, p = 0.2733). The present data emphasize the clinical significance of monitoring of cerebral blood flow and metabolism in TBI and provide evidence for metabolic coupling between astrocytes and neurons.

Distribution of Cerebral Blood Flow in the Circle of Willis

PURPOSE

To prospectively determine the effect of anatomic variations in the circle of Willis on volume flow in the internal carotid arteries (ICAs) and basilar artery (BA).

MATERIALS AND METHODS

Institutional review board approval and informed consent were obtained. Phase-contrast magnetic resonance (MR) angiography was used to measure the volume flow in the BA and ICAs in 208 patients (182 men, 26 women; mean age, 60 years) with symptomatic atherosclerosis or risk factors for atherosclerosis. Patients with steno-occlusive disease were excluded, and flow values were normalized for age. Three-dimensional time-of-flight MR angiograms were used to assess the anatomy of the circle of Willis. Differences in volume flow between a complete circle of Willis, a circle with a missing A1 segment, and a circle with a fetal-type posterior cerebral artery were analyzed (analysis of variance and Scheffe post hoc tests).

RESULTS

The ICA volume flow in subjects with a complete configuration of the circle of Willis was 245 mL/min +/- 65 (standard deviation). Flow in the contralateral ICA was significantly increased (P < .01) in subjects with a missing A1 segment (303 mL/min +/- 56) compared with control subjects and compared with flow on the ipsilateral side (214 mL/min +/- 94; P < .01). In subjects with a unilateral or bilateral fetal-type posterior cerebral artery, the ICA volume flow was increased (P < .01) and the BA volume flow was decreased (P < .01) in comparison with the flow in subjects with no fetal-type circle of Willis.

CONCLUSION

Large asymmetries in volume flow between the right and left ICAs or decreased volume flow in the BA is not necessarily caused by vascular disease but may be caused by variations in the anatomy of the circle of Willis.

Impact of head movements on morphology and flow in the internal carotid artery after carotid angioplasty and stenting versus endarterectomy

OBJECTIVE

Because stents can cause vessel angulation during movement, we hypothesized that internal carotid artery (ICA) stents might lead to alterations of cerebropetal blood flow. This study assessed three-dimensional anatomy and volumetric flow rate (VFR) in the ICA in various head positions by comparing patients treated with carotid angioplasty and stenting (CAS) with patients treated with carotid endarterectomy (CEA).

METHODS

Three-dimensional time-of-flight magnetic resonance angiography and magnetic resonance flow quantification were performed on six subjects after CAS (median age, 70 years) and on six subjects after CEA (median age, 67 years). All investigations were performed in five head positions: neutral, bent forward, bent backward, and turned to the treated, ipsilateral side and to the contralateral side. Maximum-intensity projection reconstructions were obtained to measure maximal angulation of the ICA in the forward, backward, ipsilateral, and contralateral positions compared with neutral. Subsequently, the plane perpendicular to the ICA, 1 cm distal to the stent or 4 cm distal to the carotid bifurcation (CEA patients), was established. The VFR through this plane was measured for each position, and the forward, backward, ipsilateral, and contralateral positions were compared with neutral.

RESULTS

In CAS patients, there was a median change in ICA angulation of +10.2 degrees (interquartile range, +7.3 degrees to +17.9 degrees ) in the forward position, compared with +0.2 degrees (-1.0 degrees to +2.4 degrees ) in CEA patients ( P = .016). In all other head positions, there was no statistically significant difference in angulation change. There was no statistically significant difference in VFR change between groups in any of the head positions tested.

CONCLUSIONS

There was a significant increase in ICA angulation in CAS patients if the head was bent forward; this was not observed in CEA patients. This angulation change did not lead to significant acute changes in cerebropetal blood flow, but it might have chronic effects not yet tested.

Cerebral Vasoreactivity: A Comparison of Color Velocity Imaging Quantification and Stable Xenon-Enhanced CT

OBJECTIVE

Compromised cerebral vasoreactivity increases the risk of stroke. In this study, we sought to determine whether extracranial arterial blood flow volume measured on color velocity imaging quantification could be predictive of cerebral vasoreactivity after the administration of acetazolamide.

SUBJECTS AND METHODS

Cerebral blood flow and extracranial arterial blood flow volume of 35 patients with symptomatic carotid occlusive disease were measured before and after the administration of acetazolamide on stable xenon CT and color velocity imaging quantification, respectively. The changes in unilateral extracranial arterial blood flow volume and respective hemispheric cerebral blood flow were compared. The mean difference in the percentage of change in flow volume, the 95% limit of agreement, and Cohen's kappa coefficient were calculated.

RESULTS

A total of 64 unilateral extracranial arterial blood flow volume changes were successfully compared with the changes in the ipsilateral hemispheric cerebral blood flow. The mean difference in percentage of change in flow volume between the two techniques was 4.7%, with the 95% limit of agreement ranging from -90.2% to 99.7%. Cohen's kappa coefficient was 0.41 (95% confidence interval, 0.13-0.68; p = 0.001).

CONCLUSION

The performance of color velocity imaging quantification for evaluating cerebral vasoreactivity is comparable to that of transcranial Doppler sonography. Because color velocity imaging quantification is not as limited as transcranial Doppler sonography, it could be an ideal complementary tool to transcranial Doppler sonography. More studies are required to define its clinical value.

Redistribution of cerebropetal blood flow in patients with carotid artery stenosis measured non-invasively with fast cine phase contrast MR angiography

The purpose was to evaluate the blood flow redistribution in the neck vessels of patients with internal carotid artery (ICA) stenosis. Eighty-six patients with ICA stenosis underwent contrast-enhanced magnetic resonance angiography (CEMRA) and fast 2D phase contrast (2D-PC) sequence to measure the mean blood flow (MBF) of ICA, basilar artery (BA) and middle cerebral artery (MCA). CEMRA revealed 53 severe stenoses, 45 moderate stenoses and 3 occluded vessels. Patients with a unilateral severe ICA stenosis had a significantly reduced MBF of the ICA compared to the control group; the MBF reduction of the severely stenosed ICA was less conspicuous if associated with a controlateral severe stenosis. The MBF of the BA increased significantly in the presence of the bilateral severe ICA stenosis and in the ICA occlusion. The MBF of the MCA was unchanged in the presence of various degrees of ICA stenosis. Measurement of MBF with fast PC MRA permits cerebropethal blood flow assessment and gives additional information in grading ICA stenosis. The reduced MBF of a severe ICA stenosis has to be considered with caution since it depends also on the status of the controlateral ICA and may be considered a confident parameter only in case of unilateral carotid stenosis.

Evolution of Neuroendovascular Intervention: A Review of Advancement in Device Technology

NEUROENDOVASCULAR SURGERY IS a rapidly evolving field. Each year, numerous improvements are made in the endovascular surgeon's armamentarium. This evolution in technology, which is occurring at a dizzying pace, addresses many of the current limitations of neuroendovascular approaches. The potential to improve the outcomes of our patients is tremendous, particularly because one of the most common and most devastating neurological disorders, ischemic stroke, remains largely untreated. This article presents several of the new technologies that are currently being investigated or are under development and have the potential to lead to major advances in endovascular approaches for the treatment of intracranial and extracranial diseases.

Assessment of cerebral blood flow by means of blood-flow-volume measurement in the internal carotid artery: comparative study with a 133xenon clearance technique

BACKGROUND AND PURPOSE

We sought to evaluate a new, angle-independent ultrasonic device for assessment of blood flow volume (BFV) in the internal carotid artery (ICA).

METHODS

Nineteen patients and 4 healthy volunteers were enrolled in a comparative study conducted in the Care Unit of the Division of Neurosurgery at UCLA Medical Center. All patients had been admitted because of severe brain injury: 15 patients with severe head trauma (Glasgow Coma Scale score< or =8) and 4 patients with subarachnoid hemorrhage due to aneurysm rupture. In all patients and subjects, cerebral blood flow (CBF) values obtained with the 133xenon-clearance technique were compared with BFV measurements in the ipsilateral ICA.

RESULTS

Hemispheric CBF values showed a close and linear correlation with BFV measurements (r=0.76, P<0.0001). Global CBF values showed a higher correlation with the total BFV value obtained from both ICAs (r=0.84, P<0.0001). With 37 mL x min(-1) x 100 g(-1) as a cutoff value for the ischemic range, a BFV value of 220 mL/min would yield a positive predictive value of 91.7% and a negative predictive value of 82.6% (sensitivity 73.3%, specificity 95%). Conversely, BFV sensitivity and specificity were 60% and 96%, respectively, for the hyperemic range defined by a CBF value >55 mL x min(-1) x 100 g(-1) (positive predictive value of 85.7% and negative prediction value of 85.7%).

CONCLUSIONS

BFV measurements with this new technology proved to accurately correlate with CBF values evaluated by the 133xenon-clearance technique. These results support the implementation of this technique for bedside assessment of cerebral hemodynamics in critically ill neurosurgical patients.

Color velocity imaging quantification in the detection of intracranial collateral flow

BACKGROUND AND PURPOSE

The development of intracranial collateral circulation is associated with a lower risk of stroke. A noninvasive technique that can reliably detect the presence of intracranial collaterals would be a valuable factor in the assessment of risk in patients with occlusive cerebrovascular disease.

METHODS

Color velocity imaging quantification was used to measure the blood flow volume of the common carotid and vertebral arteries in 40 patients with carotid occlusive disease. The blood flow volumes in these arteries were correlated with angiographic evidence of collaterals to establish the best cutoffs for detecting intracranial collateral circulation.

RESULTS

A blood flow volume of either > or =370 mL/min in the common carotid artery or > or =120 mL/min in the vertebral artery was indicative of the presence of intracranial collaterals. The sensitivity and specificity for the common carotid artery were 92.3% [95% confidence interval (CI), 62.1 to 99.6] and 92.1% (95% CI, 77.5 to 97.9), respectively. The sensitivity and specificity for the vertebral artery were 75.0% (95% CI, 35.6 to 95.5) and 87.5% (95% CI, 66.5 to 96.7), respectively.

CONCLUSIONS

Color velocity imaging quantification offers a noninvasive, accurate method for detecting the presence of intracranial collateral circulation and quantifying its magnitude. This technique would be a useful adjunct in screening or continuous monitoring of patients with severe carotid occlusive disease.