Quantification of neurovascular compliance with retrospectively gated phase-contrast MRI

OBJECTIVE

Neurovascular compliance (NVC) is the change in the brain's arterial tree blood volume, ΔV, divided by the change in intra-vascular blood pressure, ΔP, during the cardiac cycle. The primary aim of this work was to evaluate the performance of MRI measurement of NVC obtained from time-resolved measurements of internal carotid artery (ICA) and vertebral artery (VA) flow rates. A secondary aim was to explore whether NVC could be estimated from common carotid (CCA) flow in conjunction with prior knowledge of mean ICA and VA fractional flow rates, given the small cross-section of ICA and VA in some populations, in particular small children.

METHODS

ΔV was quantified from the blood flow rate measured at the ICA and VA for actual NVC derivation. It was further estimated from individually measured CCA flow rate and mean flow fractions ICA/CCA and VA/CCA (which could alternatively be obtained from literature data), to yield estimated NVC. Time-resolved blood flow rate in CCA, ICA and VA was obtained via retrospectively-gated 2D PC-MRI at 1.5 T in healthy subjects (N = 16, 8 women, mean age 36 ± 13 years). ΔP was determined via a brachial pressure measurement.

RESULTS

Actual and estimated mean NVC were 27 ± 15 and 38 ± 15 μL/mmHg, respectively, and the two measurements were strongly correlated (r = 0.80; p = 0.0002) with test-retest intra-class correlation coefficients of 0.964 and 0.899.

CONCLUSION

Both methods yielded excellent retest precision. In spite of a large bias, actual and estimated NVC were strongly correlated.

Changes in internal carotid and vertebral arterial wall stiffness with head movement can be detected with shear wave elastography

Background: Safe practice is important for patients with neck pain, with the potential for injury to cervical arteries. Cervical manipulation or end range techniques/positions may place considerable strain on the arteries. Altered integrity of the arterial wall may render them more susceptible to minor trauma, particularly in the upper cervical region. Screening of blood flow velocity is limited for predicting those at risk. Examining properties of the cervical arterial wall (stiffness characteristics) and their response to head movement may provide an alternate measure of arterial susceptibility.Objectives: To investigate whether shear wave ultrasound elastography can detect any changes in internal carotid (ICA) and vertebral (VA) arterial wall stiffness in neutral compared with contralateral head rotation.Design: Observational studyMethods: Shear wave ultrasound elastography was used to measure the stiffness of the ICA and VA. Shear wave velocity (m/s), indicative of arterial stiffness, was measured in both arteries proximally (C3-4) and distally (C1-2) in neutral and contralateral head rotation as were intimal thickness (mm) and flow velocity (cm/s).Results: Thirty participants (20-62 years) were successfully imaged. The VA was stiffer than ICA and it became significantly stiffer in contralateral rotation (p = 0.05). The ICA became significantly less stiff (p = 0.01). Effects were more apparent at C1-2 but significant in the ICA only (p = 0.03). Flow velocity and intimal thickness were unchanged in rotation.Conclusions: Changes in VA and ICA arterial wall stiffness can be measured with shear wave ultrasound elastography. This measure may ultimately help identify arteries with greater vulnerability to rotational stresses.

Vertebral artery terminating in posterior inferior cerebellar artery: A normal variation with clinical significance

A vertebral artery (VA) terminating in a posterior inferior cerebellar artery (PICA) is often considered to be a normal variation associated with VA hypoplasia. We aimed to investigate the clinical significance of this cerebrovascular variant. A total of 80 patients with clinically evident cerebrovascular events in posterior circulation were examined by duplex sonography and magnetic resonance angiography (MRA). Eighty healthy subjects who had MRA check-up were recruited as controls. PICA termination of the VA (PICA-VA) was identified as the VA not communicating with the basilar artery (BA) but ending into a PICA. We compared the prevalence of PICA-VA and associated hemodynamic parameters between the patients with and without PICA-VA, and investigated their relationships with VA hypoplasia. The prevalence of PICA-VA was higher in the patient group than in the controls (18.7% vs. 6.3%, p = 0.015). Most measurements (73.3%) of PICA-VA did not fit the criteria of VA hypoplasia. In comparison with the non-PICA-terminating group, the PICA-VA has a smaller diameter (3.7 ± 0.7 mm vs. 3.0 ± 0.5 mm, p < 0.001), lower mean velocity (241 ± 100 mm/sec vs. 164 ± 88 mm/sec, p < 0.01), and higher pulsatility index (1.3 ± 0.5 vs. 1.9 ± 0.6, p < 0.001). Moreover, a smaller diameter of the BA (3.2 ± 0.5 mm vs. 2.5 ± 0.9 mm, p = 0.004) and the posterior cerebral artery (PCA) (2.0 ± 0.1 mm vs. 1.6 ± 0.1 mm, p = 0.006) were also noted in the PICA-VA group. The higher prevalence of PICA-VA in the patient group with smaller diameter of VA, BA and PCA reflected its clinical significance, suggesting that PICA-VA may have a detrimental impact on cerebral hemodynamics. However, the sample is small, and further studies are needed with larger sample size for confirmation.

Doppler Sonography of Blood Flow Velocity in the Vertebral Arteries of Preterm and Term Neonates

OBJECTIVES

This study aimed to evaluate normal blood flow in the vertebral arteries and the basilar artery of preterm and term neonates by Doppler sonography.

METHODS

Blood flow in both vertebral arteries and the basilar artery was examined in 102 neonates between the biological ages of 28 and 41 weeks. Fifty-one boys and 51 girls underwent Doppler sonography. Measurements were usually undertaken at 6 days old. Systolic and diastolic flow velocities, including the resistive index, were measured and analyzed, taking into consideration biological age, weight, and sex. Anatomic aberrations of the vertebral arteries were recorded.

RESULTS

Mean blood flow values ± SD in the basilar artery were 35.2 ± 7.4 cm/s (systolic velocity) and 10.9 ± 3.5 cm/s (diastolic velocity). Mean blood flow values in the right vertebral artery were 26.8 ± 9.3 cm/s (systolic velocity) and 8.0 ± 3.7 cm/s (diastolic velocity). Mean blood flow values in the left vertebral artery were 28.6 ± 8.3 cm/s (systolic velocity) and 8.7 ± 3.3 cm/s (diastolic velocity). Systolic and diastolic blood flow in both vertebral arteries was significantly higher from 38 to 41 weeks compared with 28 to 32 and 33 to 37 weeks (P < .05). Regression analysis of systolic and diastolic blood flow velocities in the vertebral arteries versus biological age yielded significant results (P < .05).

CONCLUSIONS

Sonography is an excellent tool for examining blood flow in the basilar and vertebral arteries of premature and term neonates. Mean systolic and diastolic blood flow velocities in the vertebral arteries increase significantly with age.

The Anatomy and Physiology of the Vertebral Nerve in Relation to Cervical Migraine

The anatomy of the vertebral nerve was investigated in humans and in monkeys. The effect of stimulation of the vertebral nerve and the cervical sympathetic trunk in the monkey was studied. The vertebral nerves in man and monkey represent a series of deep grey rami communicantes which form intersegmental neural arcades around the vertebral artery between C7 and C3. Above C3 the vertebral artery is accompanied by direct branches from the C1–3 ventral rami. Electrical stimulation of either the vertebral nerve or the cervical sympathetic trunk had a minimal effect on vertebral blood flow. In contrast, sympathetic stimulation had pronounced effects on carotid flow and resistance. Anatomically and physiologically there are no grounds to support the hypothesis that irritation of the “vertebral nerve” is the pathogenetic mechanism of cervical migraine.

A non-invasive method to assess cerebral perfusion pressure in geriatric patients with suspected cerebrovascular disease

Background

Cerebral perfusion pressure (CPP) can adversely impact cerebrovascular hemodynamics but cannot be practically measured in most clinical settings. Here, we aimed to establish a representative mathematical model for CPP in geriatric patients with suspected cerebrovascular disease.

Methods

A total of 100 patients (54 males and 46 females between 60–80 years of age) with suspected cerebrovascular disease and no obvious cerebrovascular stenosis were selected for invasive CPP monitoring via catheterization of the middle segment of the common carotid arteries and openings of the vertebral arteries bilaterally. Curves were function-fitted using MATLAB 7.0, and data was statistically processed by SPSS 20.0.

Results

MATLAB 7.0 constructed eighth-order Fourier functions that fit all recorded CPP curves. Since the coefficients of the 100 functions were significantly different, all functions were standardized to derive one representative function. By manipulating the heart rate and maximum/minimum CPP of the representative function, estimated CPP curves can be constructed for patients with differing heart rates, intracranial pressures (ICPs) and blood pressures.

Conclusions

CPP can be well-modeled through an eighth-order Fourier function that can be constructed from a patient’s brachial artery blood pressure (BABP), ICP and heart rate. This function is representative of geriatric patients with cerebrovascular disease and can be used in the future study of cerebral hemodynamics.

Attenuation of blood flow pulsatility along the Atlas slope: a physiologic property of the distal vertebral artery?

BACKGROUND AND PURPOSE

Physiologic and pathologic arterial tortuosity may attenuate blood flow pulsatility. The aim of this prospective study was to assess a potential effect of the curved V3 segment (Atlas slope) of the vertebral artery on arterial flow pulsatility. The pulsatility index and resistance index were used to assess blood flow pulsatility.

MATERIALS AND METHODS

Twenty-one healthy volunteers (17 men, 4 women; mean age, 32 years) were examined with a 3T MR imaging system. Blood velocities were measured at 2 locations below (I and II) and at 1 location above the V3 segment (III) of the vertebral artery by using a high-resolution 2D-phase-contrast sequence with multidirectional velocity-encoding.

RESULTS

Pulsatility and resistance indices decreased along all measurement locations from proximal to distal. The pulsatility index decreased significantly from location II to III and from I to II. However, the decrease was more pronounced along the Atlas slope than in the straight-vessel section below. The decrease of the resistance index was highly significant along the Atlas slope (location II to III). The decrease from location I to II was small and not significant.

CONCLUSIONS

The pronounced decrease in pulsatility and resistance indices along the interindividually uniformly bent V3 segment compared with a straight segment of the vertebral artery indicates a physiologic attenuating effect of the Atlas slope on arterial flow pulsatility. A similar effect has been described for the carotid siphon. A physiologic reduction of pulsatility in brain-supplying arteries would be in accordance with several recent publications reporting a correlation of increased arterial flow pulsatility with leukoencephalopathy and lacunar stroke.

The effect of end-range cervical rotation on vertebral and internal carotid arterial blood flow and cerebral inflow: A sub analysis of an MRI study

INTRODUCTION

Cervical spine manual therapy has been associated with a small risk of serious adverse neurovascular events, particularly to the vertebral arteries. Sustained end-range rotation is recommended clinically as a pre-manipulative screening tool; however ultrasound studies have yielded conflicting results about the effect of rotation on blood flow in the vertebral arteries. There has been little research on internal carotid arterial flow or utilising the reference standard of angiography.

OBJECTIVES

To evaluate the mean effect of cervical rotation on blood flow in the craniocervical arteries and blood supply to the brain, as well as individual variation.

DESIGN

This was an observational study.

METHOD

Magnetic resonance angiography was used to measure average blood flow volume in the vertebral arteries, internal carotid arteries, and total cerebral inflow, in three neck positions: neutral, end-range left rotation and end-range right rotation in healthy adults.

RESULTS

Twenty participants were evaluated. There was a decrease in average blood flow volume in the vertebral and internal carotid arteries on contralateral rotation, compared to neutral. This was statistically significant on left rotation only. Ipsilateral rotation had no effect on average blood flow volume in any artery. Total cerebral inflow was not significantly affected by rotation in either direction.

CONCLUSIONS

It appears that in healthy adults the cerebral vasculature can compensate for decreased flow in one or more arteries by increasing flow in other arteries, to maintain cerebral perfusion. Sustained end-range rotation may therefore reflect the compensatory capacity of the system as a whole rather than isolated vertebrobasilar function.

Application of vertebral artery ultrasonography in enlistment-age male student pilots

The aim of this study was to investigate the vertebral artery (VA) morphology of enlistment-age male student pilots with ultrasound to provide a basis for early diagnosis of potentially asymptomatic cervical vertigo. Ultrasound results of the origin position, diameter and hemodynamics of the VA in 935 cases of student pilots with a mean age of 18.0 y were analyzed. The inner diameters of both sides of the VA differ: the left is larger than the right statistically (p < 0.001). Moreover, the peak systolic velocity of the left VA is significantly greater than that of the right (p < 0.001). Congenital VA anomalies in age-appropriate male student pilots included inner diameter variation, course variation and origin position variation. The incidence of course variation or origin position proportion was low (3.46%, 32/925), and origin position variation was often accompanied by inner diameter variation or course variation. This study confirms that there are a variety of congenital abnormalities in the vertebral arteries of enlistment-age male student pilots, and a VA diameter <2.5 mm may be a reasonable criterion for diagnosis of VA hypoplasia.

How does Adamkiewicz artery influence blood supply to the fetal spinal cord?

Adamkiewicz artery became important in clinical practice since it was noticed that its damage during aorta aneurysm repair surgery can sometimes lead to distal spinal cord ischemia. The complexity of anatomical variations can be related to the development of spinal cord arteries. The aim was to describe topography of Adamkiewicz artery and its relations to the anterior spinal artery in fetuses. The study was carried on 4 Batson's resin corrosion casts and 24 formalin-fixed fetuses injected with dyed gelatin or latex aged 15-24 weeks gestational age. In fixed specimens vertebral canals were dissected, the anterior spinal artery was traced and Adamkiewicz artery localized. Arteries were photographed and digitally measured. Data were afterwards statistically analyzed. Anterior spinal artery was duplicated in 3/28 cases. There were from 1 to 3 Adamkiewicz arteries per specimen, mean 1.71. No relation was found between the number of Adamkiewicz artery and age. In 37/48 cases Adamkiewicz artery emptied into the anterior spinal artery on the left side. Mean degree of narrowing in anterior spinal artery (diameter of the anterior spinal artery above junction with Adamkiewicz artery divided by its diameter under that junction) was 76.74%. The diameter of Adamkiewicz artery was also correlated linearly with the degree of narrowing of anterior spinal artery (r=0.68; p<0.05). The arteries of the anterior aspect of thoracolumbar spinal cord in the 2nd trimester of pregnancy represent the adult pattern. A potentially great impact of Adamkiewicz artery on the distal spinal cord circulation may be postulated on the basis of these morphological data.

Doppler study of the fetal vertebral and middle cerebral arteries in fetuses with normal and increased umbilical artery resistance indices

OBJECTIVE

To compare the brain sparing mechanism of the fetal vertebral artery (VA), with the one of the middle cerebral artery (MCA) in fetuses with increased umbilical artery (UA) Doppler impedance.

METHOD

We retrospectively studied 1084 Doppler examinations of the VA, MCA and UA performed in 1084 fetuses between 19 and 41 week of gestation. These were divided into 3 groups according to the UA resistance index (UA RI): group 1: UA RI < 95(th) percentile (N = 965), group 2: UA RI > 95(th) percentile (N = 111) and group 3: absent UA diastolic flow (N = 8). Afterwards, values were converted into multiples of the median (MoM), and means and standard deviations were calculated. Finally, Kruskal-Wallis tests and box and whiskers charts were applied to evaluate differences.

RESULTS

For both, the VA RI and MCA RI, no differences were seen among the groups of fetuses who maintained diastolic flow in the UA. However, the VA RI and MCA RI were lower when the UA diastolic flow was absent.

CONCLUSION

The VA and MCA work in unison, decreasing impedances only when UA flow is severely affected.

Hemodynamic characteristics of the vertebrobasilar system analyzed using MRI-based models

The vertebrobasilar system (VBS) is unique in human anatomy in that two arteries merge into a single vessel, and it is especially important because it supplies the posterior circulation of the brain. Atherosclerosis develops in this region, and atherosclerotic plaques in the vertebrobasilar confluence can progress with catastrophic consequences, including artery occlusion. Quantitative assessments of the flow characteristics in the VBS could elucidate the factors that influence flow patterns in this confluence, and deviations from normal patterns might then be used to predict locations to monitor for potential pathological changes, to detect early signs of disease, and to evaluate treatment options and efficacy. In this study, high-field MRI was used in conjunction with computational fluid dynamics (CFD) modeling to investigate the hemodynamics of subject-specific confluence models (n = 5) and to identify different geometrical classes of vertebrobasilar systems (n = 12) of healthy adult subjects. The curvature of the vessels and their mutual orientation significantly affected flow parameters in the VBS. The basilar artery geometry strongly influenced both skewing of the velocity profiles and the wall shear stress distributions in the VBS. All five subjects modeled possessed varying degrees of vertebral asymmetry, and helical flow was observed in four cases, suggesting that factors other than vertebral asymmetry influence mixing of the vertebral artery flow contributions. These preliminary studies verify that quantitative, MR imaging techniques in conjunction with subject-specific CFD models of healthy adult subjects may be used to characterize VBS hemodynamics and to predict flow features that have been related to the initiation and development of atherosclerosis in large arteries. This work represents an important first step towards applying this approach to study disease initiation and progression in the VBS.

Anatomical variations of the posterior circulation: case reports and a review of literature

INTRODUCTION

The intracranial vascular anatomical variations, although rare, represent a interesting field of research, since many anomalous variants are possible and in most cases they remain asymptomatic. The capability of the cerebral circulation to adapt to several flow changes is confirmed by the fact that in several cases these anatomical variation compensate for an eventual unsuccessful development of the normal circulation, expecially in the posterior section of cerebral circulation.

MATERIALS AND METHODS

A comprehensive review of PubMed literature was performed and three clinical cases have been analyzed.

RESULTS

Several angiographic and MR-angiography reports have been evaluated, regarding general and specific anatomical variants of the posterior circulation.

DISCUSSION

Although rare, the anatomical variations of the posterior intracranial circulation represent an interesting field of investigation in order to achieve a better comprehension of the embryological development of the circulatory system.

Role of baroreceptors in the zone of vertebral arteries in the reflex regulation of venous tone in the splanchnic basin

Pressure elevation in the reflexogenic zone of vertebral arteries was accompanied by a decrease in the tone of splanchnic veins, reduction of blood pressure, and suppression of external respiration. An opposite response of the cardiorespiratory functional system was observed under conditions of low baseline pressure in the vascular zone. Our findings and results of previous physiological and morphological studies indicate that the capacitance vessels play an important role in cardiorespiratory reactions.

Effects of tibolone on blood flow resistance and intima-media thickness of the carotid arteries: effect of time since menopause

OBJECTIVE

The aim of this prospective study was to evaluate the effects of tibolone on carotid atherosclerosis in healthy postmenopausal women.

METHODS

Twenty-five healthy postmenopausal women were included in the study. Patients received tibolone 2.5 mg daily for 6 months. Resistance indices of the common carotid artery (CCA), internal carotid artery (ICA), external carotid artery (ECA) and vertebral arteries, and intima-media thickness of the CCA were measured both at baseline and at the end of the study with ultrasonography.

RESULTS

No significant differences were observed in the resistance indices of the CCA, ICA, ECA and vertebral arteries, as well as intima-media thickness of CCA at 6 months in comparison with baseline. Tibolone significantly improved the intima-media thickness of the CCA of women who were less than 18 months since menopause.

CONCLUSION

Overall, these results demonstrate no significant effects of tibolone on either intima-media thickness or blood flow resistance in the carotid arteries in postmenopausal women. However, the results suggest that tibolone may have a positive effect on the vascular system if commenced within 18 months since menopause; this warrants further investigation.

Evaluation of coronary subclavian steal syndrome using sestamibi imaging and duplex scanning with observed vertebral subclavian steal

Coronary subclavian steal is defined as retrograde blood flow from the myocardium through the internal mammary artery graft, secondary to a proximal subclavian artery stenosis. The incidence of this syndrome in patients undergoing internal mammary artery grafts for coronary artery bypass is estimated to be 0.44%. Angiography remains the definitive diagnostic test for confirming this condition. We describe a noninvasive method for evaluating coronary subclavian steal syndrome in a 57-year-old man, with a 50-55% subclavian stenosis confirmed by angiography. Noninvasive evaluation using duplex scanning demonstrated normal vertebral artery blood flow. Technetium 99m-sestamibi (99mTc) imaging confirmed a fixed anterolateral defect. When left-arm isometric exercise was employed, retrograde vertebral artery blood flow was observed by Doppler imaging. A repeat 99mTc-sestamibi study documented an increase in tracer distribution in the anterolateral defect confirming reperfusion of the myocardium through the left internal mammary artery graft. The use of duplex scanning and 99mTc-sestamibi may serve as an adjunct in evaluating coronary subclavian steal syndrome as well as documenting transient vertebral subclavian steal in this patient population.

[Phytoaeroionotherapy of psychovegetative syndrome]

The objective of the study was to elucidate the possibility to use phytoaeroionotherapy as a component of combined correction of the functional state of patients with psychovegetative syndrome. The curative effect of the proposed methods was due to a decrease of the severity of manifestations of hypersympaticotony by 59-61%, a 2.5-2.7-fold reduction of pathological hyperactivity of heart meridian CV, and normalization of blood flow in the system of internal carotid and vertebral arteries. It was shown that a combination of magnetopuncture and phytoaeroionotherapeutic chronocorrection produced the best results by virtue of a 14% reduction of systolic blood pressure, decrease of the heart rate and cardiac work index by 20% and 31% respectively. The combination ofsoft-tissue manual therapy contributed to the improvement of characteristics of short-term memory by 51% and of intellectual work capacity by 50%.

[Baroreflexes originated in vertebral artery zones upon peripheral vein tonus, systemic arterial blood pressure, and external respiration]

The investigation was intended to study the role ofbaroreceptors ofhemodynamically isolated zone of vertebral arteries in regulation of peripheral veins tonus, arterial pressure and external respiration. Pressure decrease in this vascular reflexogenic zone led to reflex responses of increase in femoral vein tonus, elevation of blood pressure level and stimulation of external respiration. The opposite reflex responses of cardio-respiratory functional system to initial pressure activation of vertebral arteries baroreceptors are observed. Basing on generalization of our own findings and similar physiological and morphological researches of other authors, it is established that afferentation from the vertebral artery zone is a reflexogenic factor of somatic muscles' veins tonus regulation. These reflexes of capacity vessels tonic activity changes are part of cardio-respiratory responses of maintaining the tissue gaseous exchange.

Left subclavian artery occlusion by thoracic aortic stent graft: long-term clinical and duplex follow-up

BACKGROUND

In recent years there has been an increase in endovascular repair of thoracic aortic aneurysms. In cases of insufficient neck length, occlusion of left subclavian artery achieves proper sealing and is usually well tolerated. Selected cases require revascularization of the left subclavian artery, including patients after coronary bypass surgery (left internal mammary to left anterior descending) and those with arm claudication or subclavian steal syndrome.

OBJECTIVES

To evaluate the tolerability of left subclavian artery occlusion by stent graft without revascularization.

METHODS

Thirty patients with thoracic aortic aneurysms underwent endovascular repair between July 2000 and November 2004. Eleven of them had occlusion of the left subclavian artery that required revascularization in two. Follow-up (average 3 years) included: a) blood pressure measurements of both arms at rest, after effort and pulse palpation, and b) vertebral blood flow by duplex scan.

RESULTS

Of nine patients with no revascularization, 8 (89%) tolerated left subclavian artery occlusion with no claudication or steal syndrome; one (11%) suffered mild claudication only after effort and required no intervention. No left radial pulses were palpated in the nine patients. Blood pressure measurements in the left arm showed an average decrease of 40%, which remained constant after induced effort in all patients and was clinically insignificant. Duplex scan demonstrated reverse flow in the left vertebral artery in 8 of 9 patients (89%) and occlusion in 1 (originating in the arch and covered by the stent graft) with no clinical symptoms.

CONCLUSIONS

Left subclavian artery occlusion by stent graft is a tolerable procedure in the long term. In most cases, the constant decrease in blood pressure remained unchanged during follow-up and had no significant adverse affects. Most patients do not require revascularization prior to the endovascular procedure.

Study of normal Chinese vertebral–basilar arteries with transcranial color Doppler flow imaging

OBJECTIVE

The aim of this study was to evaluate the blood flow characteristics of intracranial vertebral-basilar artery (V-BA) in healthy Chinese adults with transcranial color Doppler flow imaging (TCDFI) and provide reference values of healthy people of different ages and genders.

METHODS

Three hundred healthy Chinese adults were divided into three groups based on their ages: Group I: 20-39 years, Group II: 40-59 years, Group III: >/=60 years. Each group was subdivided into two subgroups according to their gender. Peak systolic velocity (Ps), end-diastolic velocity (Vd), time average maximum velocity (TAMAX), pulsatility index (PI), and resistance index (RI) were measured from intracranial V-BA scanning.

RESULTS

Ps, Vd, and TAMAX decreased with age, while PI and RI increased in all groups. Flow velocity in women was slightly higher than that of men, and there was significant differences in group III between men and women (P<.05). However, no difference was found in the flow parameters between left and right vertebral arteries.

CONCLUSIONS

This study offered reference values of intracranial V-BA flow parameters in healthy Chinese adults and indicated that these parameters varied with age and gender.

Doppler sonography evaluation of flow velocity and volume of the extracranial internal carotid and vertebral arteries in healthy adults

PURPOSE

To measure with Doppler sonography the velocity and volume of blood flow in the extracranial internal carotid artery (ICA) and vertebral artery (VA) of healthy adults and to calculate total cerebral blood flow volume (tCBFV).

METHODS

Bilateral ICA and VA were examined sonographically in 180 healthy adults. Angle-corrected peak systolic (Vps), end-diastolic (Ved), and time-averaged maximum blood flow velocity (TAV) were measured in pulsed Doppler mode, and the resistance index (RI) and pulsatility index (PI) were calculated. The cross-sectional area (A) was measured on gray-scale images. Volume flow was calculated as FV = TAV x A, and tCBFV was calculated as the sum of the right and left ICA and VA volume flow.

RESULTS

tCBFV was 651 +/- 96 ml/min for the entire population. There was a significant decrease in Vps, Ved, TAV, and tCBFV with age in all arteries. RI and PI values initially declined and then increased with age. Cross-sectional area increased with age in ICA but not in VA. PI and RI were higher in men than in women. Blood flow velocity and volume were higher, and RI was lower in the left than in the right VA.

CONCLUSION

The Doppler sonographic assessment of extracranial ICA and VA blood flow volume may be useful for the study of cerebral hemodynamic changes in patients with cerebrovascular disorders. Age-dependent changes should be considered, for instance, in the management of intensive care patients with impaired cerebral perfusion.

Extracranial carotid Doppler ultrasound evaluation of cerebral blood flow volume in COPD patients

OBJECTIVE

Doppler ultrasound of extracranial internal carotid artery (ICA) and vertebral artery (VA) were performed and total cerebral blood flow volume (tCBFV) was evaluated in chronic obstructive pulmonary disease (COPD) patients. CBFV changes due to blood gas changes were also evaluated.

METHODS

Bilateral ICA and VA have been examined with 7.5 MHz linear array transducer in COPD patients. Angle-corrected time averaged flow velocity and cross-sectional areas of vessels have been measured. Flow volumes and tCBFV have been calculated. Flow velocities and waveform parameters have been measured.

RESULTS

tCBFV, anterior-posterior CBFVs, left-right ICA flow volumes, bilateral ICA and VA cross-sectional areas and left ICA peak-systolic velocity were significantly higher in COPD patients than control group. Among COPD patients tCBFVs were highest in hypoxemic-hypercapnic ones, and lowest in normocapnic ones. Bilateral VA flow volumes, bilateral ICA (except left ICA V(ps)) and VA flow velocities and waveform parameters were not different in COPD patients compared with control group. When compared among the subgroups of COPD patients, there were no significant differences for all parameters.

CONCLUSION

tCBFVs were found to be significantly higher in COPD patients. This increment which is probably due to balancing the oxygen deficit is low with hypoxemia and high with hypercapnia and hypoxemia. Particularly, bilateral ICA and VA cross-sectional area changes and increased left ICA V(ps) were considered as the main reason for increased tCBFV in COPD patients.

Simulation of cerebral hemodynamics for preoperative risk assessment

BACKGROUND

An important part of the medical treatment of many cerebrovascular diseases is the occlusion of brain supplying arteries. Until now, the risk of this intervention can only be estimated by invasive diagnostics including the risk of cerebrovascular accidents.

METHODS AND RESULTS

As a supporting tool, a computer model of the circle of Willis was designed. The model is based upon linear differential equations describing electrotechnical circuits extended non-linearly. By these means, time continuous simulations of different states and the online observation of all calculated state variables such as blood pressure and blood flow in every modeled vessel became feasible. For individual simulations, model parameters were determined by MR-angiography and boundary values by simultaneous Duplex-measurements in both carotid and vertebral arteries. State variables generated by the model behaved physiologically and the reaction of individual cerebrovascular systems in critical situations could be investigated by special scenarios. Inaccuracies concerning the determination of model parameters and boundary values of the used differential equations are likely to be resolved in the near future through a more careful and technically improved determination of these values.

CONCLUSIONS

Computer models of subjects were created taking in account the individual anatomical and non-linear physical properties of real vascular systems supplying the brain. Thereby information could be obtained concerning the hemodynamic effects of an iatrogenic vascular occlusion.

Transcranial Doppler grading criteria for basilar artery vasospasm

OBJECTIVE

Transcranial Doppler (TCD) criteria for basilar artery (BA) vasospasm are poorly defined, and grading criteria for vertebrobasilar vasospasm are unavailable. The purpose of the present study was to define TCD grading criteria for BA vasospasm on the basis of the absolute flow velocities and the intracranial to extracranial flow velocity ratios for the posterior circulation, and to improve the sensitivity and specificity of TCD for diagnosis of BA vasospasm.

METHODS

One hundred twenty-three patients with aneurysmal subarachnoid hemorrhage underwent 144 cerebral arteriograms with views of the BA during the acute phase of vasospasm (Days 3-14 after hemorrhage). BA diameters were measured and compared with diameters obtained from baseline arteriograms. Both BA and extracranial vertebral artery flow velocities were measured by TCD within 4 hours before the arteriogram.

RESULTS

The velocity ratio between the BA and the extracranial vertebral arteries (VA) strongly correlated with the degree of BA narrowing (r2 = 0.648; P < 0.0001). A ratio higher than 2.0 was associated with 73% sensitivity and 80% specificity for BA vasospasm. A ratio higher than 2.5 with BA velocity greater than 85 cm/s was associated with 86% sensitivity and 97% specificity for BA narrowing of more than 25%. A BA/VA ratio higher than 3.0 with BA velocities higher than 85 cm/s was associated with 92% sensitivity and 97% specificity for BA narrowing of more than 50%.

CONCLUSION

The BA/VA ratio improves the sensitivity and specificity of TCD detection of BA vasospasm. On the basis of the BA/VA ratio and BA mean velocities, we suggest new TCD grading criteria for BA vasospasm.

VASCULAR ANOMALY CAUSING SUBCLAVIAN STEAL AND CERVICAL MYELOPATHY IN A DOG: DIAGNOSIS AND ENDOVASCULAR MANAGEMENT

A 3-year-old dog with cervical myelopathy resulting from a vascular anomaly is described. Marked intradural-extramedullary spinal cord compression was observed, in association with multilevel ectatic anastomotic radicular arterial branches connecting the left and right vertebral arteries. A nonpatent proximal segment of the right subclavian artery had resulted in compensatory enlargement of the left vertebral artery. Flow within the right vertebral artery was retrograde and fed into the patent distal segment of the right subclavian artery. Multiple imaging techniques including myelography, computed tomography, magnetic resonance imaging, and selective digital angiography were used to document this anomaly. To reduce spinal cord compression the largest collateral vessel was embolized without complication. Good clinical response was observed within 6 weeks and improved clinical neurologic function was maintained at the time of a 12-month re-evaluation.

Arterial blood flow and autonomic function in full-term infants

OBJECTIVES

To investigate variations in the autonomic functions and blood-flow velocity of the arteries supplying to the brainstem in supine and prone positions.

METHODS

Forty-one full-term infants were studied at the age of 24-72 h. Each infant underwent respiratory, cardiac and eye movement analyses in supine and prone positions. In addition, blood-flow velocity of the basilar and vertebral arteries was measured with a 2 MHz probe for 5 min in each position. Two time domain measures of heart rate variability (HRV) (Standard deviation of normal R-R intervals for long-term and pNN50 for short-term variability) were employed.

RESULTS

Significantly decreased short- (P<0.001) and long (P = 0.003)-term variabilities were observed in prone when compared with supine position. Increased short-term variability in active sleep with no interaction with position was observed (P = 0.005). A significant decreased mean (P = 0.001) and peak (P = 0.001-0.003) blood-flow velocity in prone when compared with supine position were measured in all three arteries supplying to the brainstem. No significant correlation between HRV and arterial blood-flow velocity (ABFV) was observed in either position.

COMMENT

The results of the present study in agreement with previous studies reflect the vulnerability of infants in prone position as related to brainstem function. However, it appears that ABFV and autonomic functions as reflected by HRV are independent physiological measures, possibly indicating regulation autonomy of the central nervous system.

The vertebral artery: a review of anatomical, histopathological and functional factors influencing blood flow to the hindbrain

An uncompromised blood flow to the brain is essential for normal neurological function. If the blood supply to the hindbrain, via the paired vertebral arteries, is reduced sufficiently, signs and symptoms of tertebrobasilar ischaemia may result. There are several factors that may cause a reduction in vertebral artery blood flow. These include exostoses, such as the retroarticular canal and lateral bridge of the atlas vertebra that may cause compression of the related part of the vertebral artery; or atherosclerosis of the artery wall occluding the vessel lumen. Functional factors, such as sustained end-of-range rotation of the cervical spine, may cause distortion of the vertebral artery in the suboccipital region, which may be reflected as decreased blood flow in the suboccipital and intracranial parts of the artery. A combination of such factors is likely to cause reduced blood flow to the hindbrain. It is the purpose of this review to highlight some of the factors that may compromise vertebral artery blood flow and, therefore, to provide some evidence on which to base our professional practice.

The effects of normovolemic hemodilution on protein synthesis recovery following postischemic reperfusion in the rat brain

Normovolemic hemodilution is a possible way to improve the brain recovery after ischemia and reperfusion. Therefore we have decided to examine how this process may affect the post-ischemic protein synthesis machinery. We analysed rat brains after 4-vessel-occlusion and different time intervals of reperfusion using normovolemic hemodilution. We achieved an important increase of [4,5-3H]leucine incorporation into polypeptides in vitro in the rat brain neocortex 30 minutes after ischemia, but concurrently there was no significant change in the hippocampus and striatum. By extending the time course of reperfusion we did not observe any important deviation of in vitro [4,5-3H]leucine incorporation in the studied brain areas. Thus, although hemodilution increased protein synthesis in selective vulnerable regions after ischemia, this improvement is not of significant importance.

Blood-flow volume quantification in internal carotid and vertebral arteries: comparison of 3 different ultrasound techniques with phase-contrast MR imaging

BACKGROUND AND PURPOSE

Optimal estimation of cerebral blood-flow volume (BFV) may be an important indicator for better evaluation of the patients with cerebrovascular disorders. In this study, we compared the BFV values at bilateral internal carotid and vertebral arteries of healthy volunteers obtained with color Doppler, power Doppler, and B-flow ultrasound (US) studies and tried to determine which examination is more correlated with MR phase-contrast quantification.

METHODS

BFVs of the internal carotid and vertebral arteries of 40 healthy volunteers (19 men and 21 women; age range, 20-47 years) were measured by using color Doppler, power Doppler, B-flow US and MR phase-contrast imaging. The flow measurements obtained with the sonographic techniques were compared with MR phase contrast, which is accepted as the most reliable method for the estimation of cerebral BFV.

RESULTS

Quantification with power Doppler imaging showed the highest values among sonography techniques, followed by color Doppler imaging, B-flow imaging (BFI), and MR phase-contrast flow quantification. There was a statistically significant difference between the flow-volume values obtained with these 4 different techniques (P < .05). BFI yielded the closest values (internal carotid arteries, 238.84 mL/min; vertebral arteries, 51.16 mL/min) to MR phase-contrast flow quantification study with higher correlation rates.

CONCLUSION

Flow volumes obtained with BFI showed the highest correlation with MR phase-contrast imaging among 3 different sonography techniques. B-flow sonography may be a very effective and cost-efficient alternative for MR phase-contrast studies for the calculation of cerebral BFV.

Differences between left and right suboccipital and intracranial vertebral artery dimensions: an influence on blood flow to the hindbrain?

BACKGROUND AND PURPOSE

Although vertebral artery (VA) blood flow is adequate in normal circumstances, reduction in the dimensions of the vessel because of atherosclerosis, or compression or stretching, may lead to hindbrain hypoxia with serious clinical manifestations. Such effects may be more pronounced in VAs that are naturally smaller than the norm. Because normative data for the suboccipital (VA3) and intracranial (VA4) vertebral artery are not readily available, it was the aim of the present study to measure the dimensions of these distal parts of the VA, to inform professional practice of the possible influence of different vessel dimensions on blood flow to the hindbrain.

METHOD

The study was a laboratory-based observational or descriptive study. A total of 40 and 54 left and right, suboccipital and intracranial parts of the VA (n = 188 vessels), obtained from cadavers of females and males aged 20-80 years, was processed for light microscopic study and measurement of the dimensions of the vessels. The left and right inner and outer diameters, cross-sectional areas and the tunica media thicknesses were calculated in each part of the vessel and compared by use of t-tests.

RESULTS

The histological structure of the VA was typical of a muscular or distributing artery. Although, in the total number of specimens, no statistically significant differences were found between left and right sides in either part of the vessel, a larger left than right VA4 was demonstrated in the females. The VA3 was significantly larger than VA4 in males and females, and all dimensions in both parts of the vessel were greatest in the older age group.

CONCLUSIONS

Reduced VA blood flow, whether because of atherosclerosis or compression or stretching of the vessel, is more likely to occur in arteries that are smaller than normal. This information is of value to clinicians in avoiding further compromising the VA and its blood flow during professional practice.

[Assessment of patients with sudden hearing loss by transcranial Doppler ultrasonography]

OBJECTIVES

We evaluated the utility of transcranial Doppler ultrasonography in determining the vascular pathology in patients with sudden hearing loss.

PATIENTS AND METHODS

The study included 13 patients (11 males, 2 females; mean age 46.6+/-17.7 years; range 18 to 66 years) with a diagnosis of sudden hearing loss. Patients having chronic otitis media or other middle ear diseases or a history of surgery in the affected ear were excluded. All the patients were evaluated by pure-tone audiometry, impedance audiometry, transient evoked otoacoustic emissions, auditory brainstem responses, and transcranial Doppler ultrasonography. The results were compared with those of a control group of 19 age- and sex-matched healthy subjects (12 males, 7 females; mean age 46.8+/-6.9 years; range 33 to 58 years) who did not have any ear disease or a history of ototoxic drug intake or working in a noisy environment, and no pathology on otoscopic and audiometric examinations.

RESULTS

Compared to the normal ear, the mean blood flow and systolic flow velocities of the vertebral artery were significantly decreased, and the mean pulsatile index was significantly increased on the affected side. The mean flow velocity of the basilar artery in the patient group was lower than that found in the control group.

CONCLUSION

Transcranial Doppler ultrasonography can be used for the evaluation of vascular involvement of the vertebral and basilar arteries in patients with sudden sensorineural hearing loss.

Cerebral blood flow measurements of the extracranial carotid and vertebral arteries with Doppler ultrasonography in healthy adults

PURPOSE

To establish normal cerebral blood flow volume by measuring flow volume of the extracranial carotid and vertebral arteries using Doppler ultrasonography in healthy adults.

MATERIALS AND METHODS

A prospective study was performed with a group of 96 healthy adults aged 20 to 80 years (48 women, 48 men; mean age of all patients, 49.8 +/- 17.1). The common, external, and internal carotid arteries and the vertebral arteries (CCA, ECA, ICA, and VA, respectively) were examined using Doppler ultrasonography. Peak systolic velocity (PSV), end diastolic velocity (EDV), resistive index (RI), and luminal diameters of the vessels were measured, and flow volumes were calculated in all the arteries. The influence of age on these parameters was also investigated.

RESULTS

In the CCA, ICA, and VA, all flow velocities and flow volumes decreased significantly with an increase in age. The luminal diameters of the carotid and vertebral arteries increased significantly with aging, while there was no significant alteration in the RI. The luminal diameters of the CCA, ICA, and ECA were significantly smaller in women than in men. PSV and EDV in the ICA, and EDV in the VA were significantly higher in men. There was no gender-linked difference in flow volumes of the brain-feeding arteries, however, in the ECA flow volumes were significantly higher in women.

CONCLUSION

Normal cerebral blood flow volume was established by measuring the flow volume of the ECA and VA with Doppler ultrasonography in healthy adults. We believe that these data can be useful in evaluating cases with cerebrovascular disease, which are related to altered cerebral blood flow volume.

Intra-arterial thrombolysis of embolic middle cerebral artery using collateral pathways

BACKGROUND AND PURPOSE

Cervical internal carotid artery (ICA) occlusion associated with middle cerebral artery (MCA) embolic occlusion requires prompt revascularization to prevent devastating stroke. With the advent of endovascular techniques for chemical and mechanical thrombolysis, the clinical outcome of patients with major arterial occlusions will improve. Finding the most expedient pathway to the site of end organ occlusion for thrombolysis is important.

METHODS

We present two cases of acute stroke secondary to thrombotic occlusion of the cervical ICA associated with MCA embolic occlusion treated with intra-arterial thrombolysis via catheter navigation through the posterior communicating artery to the site of MCA arterial occlusion. No attempt was made to transverse the occluded ICA.

RESULTS

Near complete restoration of flow was achieved in one patient and minimal vessel reopening was observed in the other patient. Both patients had good outcomes.

CONCLUSION

Intra-arterial thrombolysis via Circle of Willis collaterals such as the posterior communicating artery for the treatment of acute thrombotic occlusion of the cervical internal carotid artery associated with embolic occlusion of the middle cerebral artery is a therapeutic option. This treatment option avoids the potential complications of navigating through an occluded proximal internal carotid artery and may expedite reopening of the MCA.

Characterization of volumetric flow rate waveforms in the normal internal carotid and vertebral arteries

Knowledge of normal cerebrovascular volumetric flow rate (VFR) dynamics is of interest for establishing baselines, and for providing input data to cerebrovascular model studies. Retrospectively gated phase contrast magnetic resonance imaging was used to measure time-resolved VFR waveforms from the two internal carotid arteries (ICA) and two vertebral arteries (VA) of 17 young, normal volunteers (16M:1F) at rest in a supine posture. After normalizing each waveform to its respective cycle-averaged VFR, the timing and amplitude of feature points from the individual waveforms were averaged together to produce archetypal ICA and VA waveform shapes. Despite significant inter-individual differences in cycle-averaged VFR within the ICA compared to VA (275+/-52 versus 91+/-18 mL min-1), the respective waveform shapes were qualitatively similar overall. The VA waveform shape did, however, exhibit significantly higher amplitudes (e.g., peak:average VFR of 1.78+/-0.30 versus 1.66+/-0.16; p<0.05) and significantly higher variability both between and within subjects. A significant correlation was observed between peak and cycle-averaged VFR, suggesting that the representative waveform shapes presented here-when scaled by an individual's cycle-averaged VFR-may be used to characterize normal ICA and VA flow rate dynamics. This capability may be of particular utility for studies where cerebrovascular flow dynamics are required, but only average flow rates are available.

Cerebellar infarcts: key features

Cerebellar infarctions often go unrecognized and misdiagnosed. Easily confused with peripheral vestibular system dysfunction, physicians often miss the cardinal symptoms of dizziness and an abnormal gait. If not treated appropriately and quickly, cerebellar infarcts can lead to coma and death. This review discusses the key features of cerebellar infarction, including the anatomical origination and clinical symptomology of the infarcts. Evaluation recommendations include neuroimaging analysis, which can help clarify the etiology and aid in making therapeutic decisions. Management of patients with cerebellar infarcts is similar to that of patients with posterior circulation ischemia. Antithrombotic drugs, thrombolytics, surgery, and angioplasty/stenting are options.

An investigation of a sympathetic innervation of the vertebral artery in primates: is there a neurogenic substrate for vasoconstriction?

Vasoconstriction of the vertebral artery may be neurogenic in origin. Although the existence of a perivascular sympathetic plexus of the vertebral artery is not in doubt, no method used to date has conclusively demonstrated a direct sympathetic innervation of the vascular smooth muscle cells and, hence, vasomotor function. It was the aim of this study, therefore, to visualise and localise noradrenergic fibres in the wall of the vertebral artery. Intracranial vertebral artery specimens (10 vervet monkeys and 10 baboon vessels) were sectioned (40 mm serial sections) and treated with anti-tyrosine hydroxylase, anti-dopamine b-hydroxylase, and anti-chromogranin-A antibodies. Some evidence of catecholaminergic fibres in the tunica adventitia but not penetrating the external elastic lamina or tunica media of the vertebral artery wall was seen. These findings were confirmed by electron microscopy. It was concluded that although a perivascular sympathetic plexus exists, the vertebral artery of primates was not shown to have a direct sympathetic innervation and a neurogenic vasoconstrictor function is unlikely.

Doppler studies evaluating the effect of a physical therapy screening protocol on vertebral artery blood flow

General and isolated cervical positional tests are used to screen for potential vertebro-basilar insufficiency (VBI). There is limited research evaluating vertebral artery blood flow in these positions to justify the rationale of progressive mechanical stress occurring to the arteries. The purpose of the study was to determine vertebral artery blood flow in six cervical positions used in clinical practice. A comprehensive cervical assessment was conducted on 22 men and women (mean age 35) with no known vascular pathology. Vertebral artery peak systolic (PS), end diastolic (ED) flow rates and resistive index (RI) were measured using duplex colour Doppler sonography (sampling at C3-C5) in neutral, rotation, extension, combined rotation-extension, combined rotation-extension-traction, deKelyn's position and a C1-C2 pre-manipulative hold. Results showed there was a significant decrease in PS and ED in the contra-lateral artery during the pre-manipulative hold, and a decrease in ED in the contra-lateral artery during rotation. There was no effect of age, gender or mobility restriction on these blood flow changes. The pre-manipulative hold had the greatest response with 34% of the arteries demonstrating a complete cessation of ED flow. In conclusion the pre-manipulative hold and rotation created the greatest mechanical stress to the contra-lateral vertebral artery. These two positions may be useful screening positions to identify individuals at risk for VBI due to inadequate collateral blood flow.

The development of haemodynamics in the extracranial cerebral arteries of healthy preterm and term neonates

To investigate the development of cerebral haemodynamics in healthy preterm and term newborns, a prospective colour duplex sonography study was performed in 113 neonates at 32 to 42 weeks of postmenstrual age. In the extracranial internal carotid arteries (ICAs) and vertebral arteries (VAs), luminal diameters and angle-corrected flow velocities were measured. Flow volumes and waveform parameters were calculated. There were no side-to-side or gender-related differences for any of the parameters measured. A marked increase of luminal diameters, end-diastolic and time-averaged flow velocities and flow volumes with postmenstrual age was found in both ICA and VA (p </= 0.0001). Peak systolic velocity did not vary with age, thus, leading to a significant decrease of the resistance and pulsatility indices with rising postmenstrual age. Reference data for flow velocities, waveform parameters, luminal diameters and flow volumes of both ICA and VA are provided for different groups of postmenstrual age. In conclusion, the marked increase in cerebral blood flow volume with postmenstrual age is due to a rise in the luminal diameter of extracranial cerebral arteries and a decrease in peripheral vascular resistance.

[Radiologic investigation of vertebrobasilar insufficiency and quantification of vertebrobasilar flow with magnetic resonance imaging]

PURPOSE

To evaluate the contribution of cervical spine radiograms, Doppler US, cervical and cranial MRI, MRA and two dimensional quantification flow in the diagnosis of vertebrobasilar insufficiency.

MATERIALS AND METHODS

We prospectively examined 25 patients having signs of vertebrobasilar insufficiency (16 females and 9 males, aged 34 to 74 years) and 25 controls of the same age and sex with MRI, MRA, Doppler US and cervical radiograms. Cervical spine radiograms were evaluated for the presence of degenerative changes, osteophytes and loss of height. The flow velocities of the basilar artery and vertebral arteries were measured with two dimensional quantification flow, using time-velocity graphics achieved by means of a region of interest drawn on transverse sections of the vessels. Posterior circulation in farcts and slow flow in vertebrobasilar system arteries were investigated on brain MR images and the presence of cervical osteophytes, spinal cord compression and the effect of the presence of degenerative changes on vertebral arteries were evaluated on cervical MR images. Paired samples T-test, independent samples T-test, Wilcoxon W, Mann-Whitney U and chi-square tests were used for statistical analysis. The significance level was taken at p below 0.05.

RESULTS

From the statistical analysis, we found that there were more pathologic findings on MRA within the patient group compared with the controls (p = 0.002). The velocities measured by MRI were significantly affected by the presence of unknown bright objects on brain MR images, osteophytes on cervical MR images, loss of height and the presence of osteophytes on radiograms in patients having VBI signs, when compared to the controls. In both groups, the measurements of flow velocity in vertebral arteries by Doppler US did not correlate with the measurements by two dimensional quantification flow.

CONCLUSION

Among the methods we used in our study, MRA was the most specific in the diagnosis of patients with vertebrobasilar insufficiency. However, two dimensional quantification flow can be used as a noninvasive but indirect method to investigate the influence of several factors on the hemodynamics.

Automatic model-based contour detection and blood flow quantification in small vessels with velocity encoded magnetic resonance imaging

RATIONALE AND OBJECTIVES

The quantitative assessment of blood flow in peripheral vessels from phase-contrast magnetic resonance imaging studies requires the accurate delineation of vessel contours in cross-sectional magnetic resonance images. The conventional manual segmentation approach is tedious, time-consuming, and leads to significant inter- and intraobserver variabilities. The aim of this study was to verify whether automatic model-based segmentation decreases these problems by fitting a model to the actual blood velocity profile.

METHODS

In this study 2 new fully automatic methods (a static and a dynamic approach) were developed and compared with manual analyzes using phantom and in vivo studies of internal carotid and vertebral arteries in healthy volunteers. The automatic segmentation approaches were based on fitting a 3D parabolic velocity model to the actual velocity profiles. In the static method, the velocity profiles were averaged over the complete cardiac cycle, whereas the dynamic method takes into account the velocity data of each cardiac time bin individually. Materials consisted of the magnetic resonance imaging data from 3 straight phantom tubes and the blood velocity profiles of 8 volunteers.

RESULTS

For the phantom studies, the automatic dynamic approach performed significantly better than the manual analysis (intraclass correlations [ICC] of 0.62-0.98 and 0.30-0.86, respectively). For the assessment of the total cerebral blood flow in the in vivo studies, the automatic static method performed significantly better than the manual 1 (ICC of 0.98-0.98 and 0.93-0.95, respectively). However, the automatic dynamic method was not significantly better than the manual 1 (ICC = 0.92-0.96) but had the advantage of providing additional parameters.

CONCLUSION

Blood flow in magnetic resonance images of small vessels can be assessed accurately, rapidly, and fully automatically using model-based postprocessing by fitting a first approximation of the velocity profile to the actual flow data.

Isolation of the arterial supply to the carotid and central chemoreceptors in the sheep

The aim of our study was to develop and validate a simple surgical model in the sheep which allows control of the gas composition of the blood supplying the carotid and central chemosensitive area independently of the rest of the body. This approach was made possible due to the specific features of the cranial circulation in the sheep. An extracorporeal circuit, consisting of a pump and a gas exchanger, was placed at the level of the two common carotid arteries to create a pressure gradient between the carotid and the systemic systems and to reverse blood flow in the vertebral vessels via the occipital arteries. When a pressure gradient of about 40 Torr was created between the systemic and carotid circulation, we found that no blood could reach the carotid bodies and the medulla without passing though the extracorporeal circulation. This was established (1) by measuring vertebral blood flow; and (2) by injecting either a coloured suspension or particles labelled with (99m*)Tc into the systemic or the carotid circulation. The slope of the relationship between minute ventilation (V(E)) and systemic arterial P(CO2) (P(a,CO2)) during high CO(2) inhalation in seven hyperoxic vagotomised and anaesthetised sheep was dramatically reduced, but remained above zero, when P(a,CO2) was maintained constant in the cephalic circuit (0.11 +/- 0.15 vs. 0.70 +/- 0.35 l min(-1) Torr(-1) for the control tests). This residual V(E) response to CO(2) inhalation remains to be explained since it could not be accounted for by any of the chemical or circulatory changes occurring in the cephalic circulation. Nevertheless, this preparation provides an easy method of maintaining chemical and circulatory homeostasis at the chemoreceptor level.