Intracranial Flow Velocity Research Articles

Intracranial Flow Velocity Quantification Using Non-Contrast Four-Dimensional Flow MRI: A Prospective Comparative Study with Transcranial Doppler Ultrasound.

Four-dimensional (4D) flow magnetic resonance imaging (MRI) allows three-dimensional velocity encoding to measure blood flow in a single scan, regardless of the intracranial artery direction. We compared blood flow velocity quantification by non-contrast 4D flow MRI and by transcranial Doppler ultrasound (TCD), the most widely used modality for measuring velocity. Twenty-two patients underwent both TCD and non-contrast 4D flow MRI. The mean time interval between TCD and non-contrast 4D flow MRI was 0.7 days. Subsegmental velocities were measured bilaterally in the middle cerebral and basilar arteries using TCD and non-contrast 4D flow MRI. Intracranial velocity measurements using TCD and non-contrast 4D flow MRI demonstrated a strong correlation in the bilateral M1, especially at the proximal segment (right r = 0.74, left r = 0.78; all p < 0.001). Mean velocities acquired with 4D flow MRI were approximately 8 to 10% lower than those acquired with TCD according to the location of M1. Intracranial arterial flow measurements estimated using non-contrast 4D flow MRI and TCD showed strong correlation. 4D flow MRI enables simultaneous assessment of vascular morphology and quantitative hemodynamic measurement, providing three-dimensional blood flow visualization. 4D flow MRI is a clinically useful sequence with a promising role in cerebrovascular disease.

Patterns of transcranial doppler flow velocities in recent ischemic stroke patients

Context:Intracranial atherosclerosis is a common cause of stroke in India. Transcranial Doppler (TCD) provides a noninvasive way to study basal intracranial blood vessels. The Oxfordshire Community Stroke Project (OCSP) classification is a simple clinical stroke classification system that has prognostic significance and has been associated with size and location of the infarct.Aim:This study was undertaken to identify patterns of TCD abnormalities in our stroke population particularly in relation to the OCSP classification.Setting and Design:A cross-sectional study was conducted at a tertiary care center in South India.Methods:Recent nondisabling ischemic stroke patients were studied. TCD was used to insonate bilateral middle cerebral, bilateral anterior cerebral, bilateral vertebral, and basilar arteries. Mean flow velocity was used to define normal or abnormal flow as per standard criteria.Statistical Methods:Association between abnormal flow velocities and OCSP classification was studied using Chi-square tests. Univariate and multivariate analysis was performed to determine factors associated with abnormal flow velocities.Results:Of the 59 participants studied, 42 (71%; 95% confidence interval [CI]: 57.3-84.7%) had abnormal flow velocities in one or more vessels and this was significantly associated with smoking (odds ratio = 5; 95% CI: 1.2–21.8). All abnormal flow velocities were blunted flow velocities. Anterior circulation flow velocity abnormalities were seen among all OCSP stroke subtypes, but posterior circulation flow abnormalities were associated with posterior circulation infarcts (P = 0.03).Conclusion:Intracranial flow velocity abnormalities are frequent among Indian stroke population. Further studies are needed to characterize these abnormalities fully.

Carotid Vibro-Compression: A Reperfusive Treatment for Acute Ischemic Stroke? Feasibility Data and a Potential Risk / Benefit Discussion in View to Animal Testing

Slow uncertain reperfusion in Acute Ischemic Stroke (AIS) by intravenous thrombolysis has prompted search for alternative therapies. Pressure/flow disturbances from rapid compressions (20 – 24 Hz) of a clotted flow tube remote from thrombosis site have shown to assist reflow. Carotid Vibro-Compression (VC), a potentially risky maneuver, may therefore enhance AIS reperfusion but verification is needed that vibro-compressions would transmit flow disturbances to the cerebral arteries. From a pool of 15 volunteers (mean age 48) carotid compressions (5 to 8 Hz, < = ~1 cm) (n =11) and vibration (30 Hz ~ 1 mm) (n = 10) were independently and together implemented with ipsilateral and contralateral Doppler flow monitoring of an intra-cranial artery. Doppler pulses from compressions were immediately demonstrated in all vessels (26 / 26) under all conditions. Pulses from vibration were observable in a majority of vessels (22 / 25), but signals were often challenging to obtain. Mean intra-cranial flow velocities trended to increase during compressions (46.1 ± 6 .4 cm/s vs. 44.0 ± 4.9 cm/s), but the difference was not statistically significant (p = 0.06). Carotid VC reliably transmits flow pulses to the cerebral vasculature, however vibration requires biofeedback to ensure device positioning. Carotid VC appears feasible for animal testing, but safety remains a major question.

Predictive Value of Intracranial Flow Velocity for In-Hospital Mortality in Patients With Traumatic Brain Injury

To investigate the predictive value of intracranial blood flow velocity on in-hospital mortality in patients with traumatic brain injury (TBI), transcranial Doppler ultrasonography was performed in patients with mild (n=30), moderate (n=35), and severe (n=33) TBI. Bilateral middle cerebral artery was examined by transcranial Doppler ultrasonography and the time-averaged mean (Vm) velocities were used for analysis. Accelerated flow velocity (>65 cm/s) was detected in 57 (58.3%) patients. The proportion of patients with accelerated flow velocity in the moderate (62.9%) or severe TBI (69.7%) group was higher than in the mild TBI group (40%, P<0.01). Decelerated flow velocity (<35 cm/s) was detected in 11 (16.1%) patients. Five patients died during hospitalization. After adjusting age, the Glasgow Coma Scale score, and treatment measures (surgical or nonsurgical), a low flow velocity (<30 cm/s) was an independent predictor for in-hospital mortality (adjusted risk ratio, 3.6; 95% confidence interval, 1.32-11.62; P=0.01). We conclude that decelerated intracranial flow can be found in <20% of the patients with severe TBI, and a persistent flow velocity <30 cm/s is indicative of a poor clinical outcome such as in-hospital mortality.

Real-Time Hemodynamic Assessment of Downstream Effects of Intracranial Stenoses in Patients with Orthostatic Hypoperfusion Syndrome

Background: Arterial flow velocity changes on transcranial Doppler can reflect changes in cerebral flow during position-induced ischemia if obtained during short-term monitoring of positional changes. Subjects and Methods: Our multicenter group monitored symptomatic and asymptomatic arteries in patients with recurrent neurological deficits during positional changes and documented intracranial arterial stenosis. Bilateral posterior cerebral and middle cerebral arteries were monitored dependent on clinical symptom localization. The symptomatic artery was monitored distal to the intracranial stenosis, and mean flow velocities (MFV) were recorded at different body positions. The symptomatic artery relative MFV ratio was defined as the ratio of symptomatic artery MFV in the asymptomatic position – MFV in the symptomatic position/MFV in the asymptomatic position. Results: Sixteen patients underwent transcranial Doppler monitoring: mean age 62 ± 19 years, 11 (69%) men, 6 (40%) with transient ischemic attacks. Ten patients (63%) had posterior and 6 anterior circulation symptoms. Patients developed neurological symptoms while standing up (63%) and/or sitting (44%), walking (13%) or during neck extension (6%). Symptomatic artery MFV dropped by ≧25% from the resting to the symptomatic position in all patients except for one. The mean symptomatic artery MFV relative ratio was higher compared with the mean asymptomatic artery MFV relative ratio: 0.5 ± 0.28 versus –0.02 ± 0.1 (p = 0.001, Wilcoxon test). The symptomatic artery relative ratio of >0.25 had a 94% sensitivity and 100% specificity for predicting neurological symptom development during testing (ĸ = 0.9, p < 0.001). Conclusions: A significant reduction in intracranial flow velocity distal to an intracranial stenosis can identify patients whose symptoms can worsen with positional changes. These patients may prove a target for interventional revascularization techniques.

Quantitative volumetry in patients with carotid disease--effects of acetazolamide.

The intracranial effects of acetazolamide on flow velocities can be monitored noninvasively by transcranial Doppler (TCD) sonography. Extracranial volume flow changes can now reliably be measured with color duplex M-mode systems. The authors tested the volumetric effects of acetazolamide in patients with high-grade unilateral carotid disease to quantify the amount of flow changes. Patients in group 1 had a high-grade > 70% internal carotid artery (ICA) stenosis, without collateral flow through the ophthalmic artery (OA). Patients with occluded ICA were included in group 2 (patent OA collateralization) or group 3 (no OA collateralization) (n = 6 per group). In group 1, common carotid artery (CCA) volume flow in the stenotic (normal contralateral) side increased from 271 (388) ml/min by 52 (54%) with 1 g aceta-zolamide intravenously. Simultaneously, middle cerebral artery (MCA) flow velocities increased from 54 (56) cm/s by 47 (53%). In group 2, extracranial volume flow increased from 166 (444) ml/min by 19 (52)%. MCA flow velocities increased from 43 (65) cm/s by 13 (30)%. In group 3, volume flow increased from 159 (467) ml/min by 2 (46)%. Intracranial flow velocities rose from 49 (54) cm/s by 27 (41)%. Volume flow data showed the expected decline in patients with high-grade ICA stenosis and even more pronounced in patients with occlusion of the vessel. Cerebral reserve capacity was less sufficient in patients with a patent OA, despite an additional supply of 30 ml/min, indicating a hemodynamically critical situation.

Carotid and transcranial color-coded duplex sonography in different types of carotid-cavernous fistula.

Patients with carotid-cavernous fistula (CCF) may undergo direct or indirect shunting. Ultrasonography has value that is complementary to angiography in the assessment and follow-up of these patients. The aim of this study was to characterize findings provided by carotid duplex sonography (CDS) and transcranial color-coded duplex sonography (TCCD) in patients with different types of CCF. CDS and TCCD were independently performed by technologists and neurologists. Digital subtraction or MR angiography was interpreted by a neuroradiologist. Ultrasonographic studies were categorized into 4 types: I, direct shunting only; II, direct shunting with a carotid aneurysm; III, indirect shunting only; and IV, mixed (direct and indirect) shunting. In addition to carotid and intracranial flow velocities, volume, and pulsatility, other direct and indirect ultrasound signs of shunting were evaluated. The direct sign of CCF was a mosaic flash detected by TCCD. Alteration of hemodynamic parameters on CDS and demonstration of draining veins with the use of TCCD were considered indirect signs. Fifteen patients (8 men, 7 women) were included in the study. According to angiographic results, patients in ultrasonographic classification types I (n=7) and II (n=3) corresponded to type A of Barrow's classification. Patients with type III (n=8) were Barrow's type C. Type IV (n=1) had a combination of Barrow's types A and C. On ultrasound, both direct and indirect signs were seen in types I, II, and IV CCF. The presence of a 2-colored oval mass divided by a zone of separation without turbulence differentiated type I from type II CCF. All patients with type III CCF had indirect signs, and only 1 patient had direct signs on TCCD. Abnormal TCCD findings were most commonly seen through the transorbital window (100%), followed by the transtemporal window (63%) and transforaminal window (40%). If only indirect ultrasonographic signs of CCF are present, TCCD can be used to predict an indirect CCF type on the basis of the origin of the fistula. With direct communication between carotid artery and cavernous sinus, both direct and indirect ultrasonographic signs can be found. The combination of CDS/TCCD may provide a noninvasive and reliable way to classify patients with CCF.

Influence of acetazolamide and CO2 on extracranial flow volume and intracranial blood flow velocity.

The vasomotor response can be tested by means of transcranial Doppler sonography. If a constant vessel diameter is assumed, the flow velocity changes will reflect blood flow volume changes. This hypothesis is difficult to verify. Simultaneous assessment of intracranial flow velocity and extracranial flow volume changes may solve this problem. We tested vasomotor response in 32 volunteers (age, 42+/-18 years) with 5% CO2. Acetazolamide (1 g) was tested in 15 volunteers (age, 28+/-8 years). To evaluate drug-dependent flow changes in the external carotid artery territory, acetazolamide was administered in 7 patients with unilateral occlusion of the internal carotid artery without evidence of collateralization through the ophthalmic artery (age, 67+/-12 years). Simultaneous recording included measurements of flow volume in the common carotid arteries (M-mode color duplex system) and flow velocity in the middle cerebral arteries. With CO2 and acetazolamide, intracranial flow velocity increased by 31% and 39%, respectively, with a simultaneous increase of common carotid artery flow volume of 47% and 50%, respectively. No change in extracranial flow volume was observed in patients with an occluded internal carotid artery. These data show not only the expected increase of flow velocity in the middle cerebral artery but also suggest an increase in cross-sectional vessel diameter of 6% and 4% with CO2 and acetazolamide, respectively. It remains unresolved whether this observation is due to a direct effect of the drug on the vessel walls or is simply pressure dependent.

Dopplersonographisches Monitoring einer A. carotis interna - Dissektion unter ungünstigen Kollateralisationsbedingungen

We report on a patient with unilateral dissection of the ICA who initially presented with a severe distal ICA stenosis. Subsequent occlusion of the ICA was followed by a large subcortical infarction. CT and MRI demonstrated a pattern of characteristic low-flow infarction. Extracranial (ECD) and transcranial (TCD) Doppler sonography initially revealed findings characteristic of distal carotid artery stenosis and later complete ICA occlusion. Doppler sonography showed diminished intracranial flow velocities and no collateral flow could be detected via the anterior and posterior communicating arteries. In this case we used TCD follow-up examinations to initiate and determine the duration of limited therapeutically induced hypertensive treatment, and were able to document the improvement of cerebral perfusion. We conclude that TCD monitoring after ICA dissection will not only enable diagnosis but also follow-up of the intracranial collateralisation to initiate and control hypertensive hypervolemic treatment in specific cases of absent collateral pathways via the circle of Willis.

Age dependence of flow velocities in basal cerebral arteries.

Flow velocities in the basal cerebral arteries were studied by transcranial Doppler sonography. A longitudinal study was undertaken on 25 healthy newborn babies during the first 20 days of life, and a cross sectional study was performed on 112 healthy children between 1 day and 18 years of age. A rapid linear increase of flow velocities was found within the first 20 days with higher velocities in neonates of higher birth weight and gestational age. Maximal values were recorded at the age of 5 to 6 years. After that the velocities decreased linearly to 70% of their maximum at the age of 18 years. Reference values were derived from the data considering age and birth weight. The increasing flow velocities probably reflect the increasing cerebral blood flow during the first years of life. Our results also support the hypothesis of a decrease in cerebrovascular resistance during infancy. With the technique of transcranial Doppler sonography and the introduced reference values normal and abnormal intracranial flow velocities can now be assessed by non-invasive methods in all paediatric age groups.

Regional cerebral blood flow and vertebral angiography at rest and in connection with arm work in patients with the "subclavian steal phenomenon".

Vascular anatomy and haemodynamics of the vertebro-basilar system were investigated by means of vertebral angiography as well as rCBF measurements using the 133Xenon clearance method in 12 patients with occlusive disease of the subclavian artery. Prior to the investigation, the occlusive lesions had been demonstrated by aortocervical angiography, which in 9 out of 12 patients showed reversed vertebral blood flow at rest. All selective vertebral angiographies and rCBF measurements were performed at rest and in connection with graded arm exercise. Patients with the subclavian steal phenomenon were found to have a slightly reduced rCBF. After arm exercise, the intracranial flow velocity of contrast medium in the cerebral vessels remained unchanged, while the velocity of the reversed flow of contrast medium in the vertebral artery was increased. Regional cerebral blood flow in the vertebro-basilar system increased during arm exercise, the average increase being about 16%. The augmentation of flow is probably due to activation of neuronal processes within the brain. The magnitude of these flow alterations in healthy individuals is unknown.