Microelectrode for measuring local cortical oxygen tension and blood flow in the same microareas of cat cortex

Abstract

The purpose of this study is to investigate the relationship between changes in cortical Po₂ (bPo₂) and cortical blood flow when inhalatingdifferentoxygen mixtures. Experiments were performed on 31 cats anaesthetized with N₂O/O₂ plus supplemental drugs for immobilization and analgesia.

Cortical Po₂ was measured by the polarographic method using 25μ Pt electrode (coated) and a 250μAg-AgCl₂ indifferent electrode, especially designed to rest lightly on the cortex by means of coiled spring support Using the same electrode but with opposite tip polarization; local cortical blood flow (ICoBF) was measured at the same site by the H₂-clearance method. The change of bPo₂ in going from FiO₂ 25% to FiO₂ 75% was measured at 58 different sites. (Table 2). At 25% Fi02 the mean bPo₂ was 24 ± 16 mm Hg, with a range from 4 to 92 mm Hg. With increased FiO₂ to 75% local bPo₂ responded quite differently at adjacent sites. At 75% FiO₂ the mean bPo₂ was 42.7 ± 32 mm Hg with a range from 10 mm Hg to 198 mm Hg. The bPo₂ and ICoBF were both measured at 44 of the 58 different sites. Cortical sites with a resting bPo₂ greater than 30 mm Hg at 25% FiO₂ had a ICBF = 57 ±12 ml/100g m; whereas sites with resting normoxic bPO₂ less than 20 mm Hg had a mean ICoBF = 56 ±14 ml/100g min.

At the cortical sites where the bPo₂ more than doubled when the FiO₂ was changed from 25 to 75%, the ICoBF was 56 ± 12 ml/100g min and at sites where the change in bPo₂ less than doubled, the ICoBF was 55 ± 13 ml/100g min. Statistically, however, those sites with a higher resting bPo₂ reacted with a greater change to an elevation of FiO₂ from 25% to 75%, although there were individual sites that reacted without relation to the resting bPo₂.     

Optical measurement of mouse strain differences in cerebral blood flow using indocyanine green

C57BL/6 mice have more cerebral arterial branches and collaterals than BALB/c mice. We measured and compared blood flow dynamics of the middle cerebral artery (MCA) in these two strains, using noninvasive optical imaging with indocyanine green (ICG). Relative maximum fluorescence intensity (I_max) and the time needed for ICG to reach I_max in the MCA of C57BL/c were lower than that in BALB/c mice. Moreover, the mean transit time was significantly lower in C57BL/6 than in BALB/c mice. These data suggest that the higher number of arterial branches and collaterals in C57BL/6 mice yields a lower blood flow per cerebral artery.     

Cerebral blood flow response to functional activation

Cerebral blood flow (CBF) and cerebral metabolic rate are normally coupled, that is an increase in metabolic demand will lead to an increase in flow. However, during functional activation, CBF and glucose metabolism remain coupled as they increase in proportion, whereas oxygen metabolism only increases to a minor degree—the so-called uncoupling of CBF and oxidative metabolism. Several studies have dealt with these issues, and theories have been forwarded regarding the underlying mechanisms. Some reports have speculated about the existence of a potentially deficient oxygen supply to the tissue most distant from the capillaries, whereas other studies point to a shift toward a higher degree of non-oxidative glucose consumption during activation. In this review, we argue that the key mechanism responsible for the regional CBF (rCBF) increase during functional activation is a tight coupling between rCBF and glucose metabolism. We assert that uncoupling of rCBF and oxidative metabolism is a consequence of a less pronounced increase in oxygen consumption. On the basis of earlier studies, we take into consideration the functional recruitment of capillaries and attempt to accommodate the cerebral tissue''s increased demand for glucose supply during neural activation with recent evidence supporting a key function for astrocytes in rCBF regulation.     

Regional cerebral oxygen utilization and blood flow in normal man using oxygen-15 and positron emission tomography

Quantitative determination of regional cerebral blood flow (rCBF), regional cerebral oxygen utilization (rCMRO₂) and regional oxygen extraction ratio (rOER) was performed in 11 normal volunteers by an oxygen-15 inhalation method and positron emission tomography.
Regional values comparable with figures from the literature have been obtained.
This non-invasive approach offers the possibility of a simultaneous quantitative evaluation of these physiological parameters in health and disease.     

Effects of aging on cerebral blood flow, oxygen metabolism, and blood oxygenation level dependent responses to visual stimulation

Calibrated functional magnetic resonance imaging (fMRI) provides a noninvasive technique to assess functional metabolic changes associated with normal aging. We simultaneously measured both the magnitude of the blood oxygenation level dependent (BOLD) and cerebral blood flow (CBF) responses in the visual cortex for separate conditions of mild hypercapnia (5% CO(2)) and a simple checkerboard stimulus in healthy younger (n = 10, mean: 28-years-old) and older (n = 10, mean: 53-years-old) adults. From these data we derived baseline CBF, the BOLD scaling parameter M, the fractional change in the cerebral metabolic rate of oxygen consumption (CMRO(2)) with activation, and the coupling ratio n of the fractional changes in CBF and CMRO(2). For the functional activation paradigm, the magnitude of the BOLD response was significantly lower for the older group (0.57 +/- 0.07%) compared to the younger group (0.95 +/- 0.14%), despite the finding that the fractional CBF and CMRO(2) changes were similar for both groups. The weaker BOLD response for the older group was due to a reduction in the parameter M, which was significantly lower for older (4.6 +/- 0.4%) than younger subjects (6.5 +/- 0.8%), most likely reflecting a reduction in baseline CBF for older (41.7 +/- 4.8 mL/100 mL/min) compared to younger (59.6 +/- 9.1 mL/100 mL/min) subjects. In addition to these primary responses, for both groups the BOLD response exhibited a post-stimulus undershoot with no significant difference in this magnitude. However, the post-undershoot period of the CBF response was significantly greater for older compared to younger subjects. We conclude that when comparing two populations, the BOLD response can provide misleading reflections of underlying physiological changes. A calibrated approach provides a more quantitative reflection of underlying metabolic changes than the BOLD response alone.     

Spasm index in subarachnoid haemorrhage: consequences of vasospasm upon cerebral blood flow and oxygen extraction

A spasm index, defined as transcranial Doppler detected flow velocity in the middle cerebral artery divided by regional cortical cerebral blood flow (CBF), was used on 24 patients with subarachnoid haemorrhage (SAH). The aim was to estimate degree and time course of vasospasm, even in cases with great day-to-day variation in CBF, and correlate to CBF and oxygen extraction. All patients showed increase in spasm indices with peak index in the second or third week. The index seemed stable in spite of day-to-day fluctuations in CBF. Severe vasospasm were associated with poor clinical condition, reduced CBF (less than 30) and high AVDO2. The same picture could be seen with minor degree of vasospasm, probably, in some cases, due to high intracranial pressure. The results suggest that the spasm index is useful in monitoring patients with subarachnoid haemorrhage, and that severe vasospasm has a negative influence on clinical condition, CBF and oxygen extraction.     

Alterations in cerebral oxygen metabolism after traumatic brain injury in children

Traumatic brain injury (TBI) is the most common cause of acquired disability in children. Metabolic defects, and in particular mitochondrial dysfunction, are important contributors to brain injury after TBI. Studies of metabolic dysfunction are limited, but magnetic resonance methods suitable for use in children are overcoming this limitation. We performed noninvasive measurements of cerebral blood flow and oxygen metabolic index (OMI) to assess metabolic dysfunction in children with severe TBI. Cerebral blood flow is variable after TBI but hypoperfusion and low OMI are predominant, supporting metabolic dysfunction. This finding is consistent with preclinical and adult clinical studies of brain metabolism and mitochondrial dysfunction after TBI.     

Hyperbaric oxygen therapy for cerebral blood flow and electroencephalogram in patients with acute cerebral infarction ——Choice for therapeutic occasion

BackgroundHyperbaric oxygen (HBO) therapy increases blood oxygen content, changes cerebral blood flow (CBF) and cerebral metabolism. Its therapeutic effects on cerebrovascular disease have been fully confirmed, but the occasion for HBO therapy is still unclear.ObjectiveTo observe the therapeutic effects of HBO therapy at different time on CBF and electroencephalogram (EEG) in patients with acute cerebral infarction (CI).DesignRandomized controlled trial.SettingDepartment of Neurology, Shidong Hospital, Yangpu District of Shanghai.ParticipantsNinety-six inpatients with acute CI, admitted to Department of Neurology, Shidong Hospital, Yangpu District of Shanghai from January 2001 to December 2006, were involved in this experiment. The involved participants met the diagnosis criteria of acute CI and confirmed by skull CT or MRI. They all were patients with moderate CI (16–30 points) according to neurologic deficit score formulated by Chinese Medical Association. Informed consents of detected items and therapeutic regimen were obtained from all the involved participants. They were randomized into two groups with 48 in each: early-stage treatment group and advanced-stage treatment group. Among the 48 patients in the early-stage treatment group, 21 male and 27 female, aged 53–68 years, 22 patients were found with basal ganglia infarction, 10 with brain lobe infarction, 16 with multiple infarction, 27 accompanied with hypertension and 2 accompanied with diabetes mellitus. Among the 48 patients in the advanced-stage treatment group, 23 male and 25 female, aged 52–71 years, 25 patients were found with basal ganglia infarction, 10 with brain lobe infarction, 12 with multiple infarction, 1 with brain stem infarction, 28 accompanied with hypertension and 1 accompanied with diabetes mellitus.MethodsAfter admission, patients of two groups received routine drug treatment.

Patients in the early-stage treatment group and advanced-stage treatment group began to receive HBO therapy within one week of CI and 4 weeks after CI, respectively. The total course of treatment both was 2 weeks. EEG examination was carried out before and after therapy, and CBF was determined with ¹³³Xe inhalation.

Assessment criteria of curative effects: Basically cured: neurologic symptoms and body signs disappeared, could work and do housework; Markedly effective: score of neurologic deficit was decreased by over 21 points, could manage himself/herself partially; Effective: score of neurologic deficit was decreased by 8 to 12 points; Non-effective: Score was increased or decreased less than 8 points, neurologic deficit was worsened, even died. Total effective rate = (number of cured+number of markedly effective+number of effective)/number of total cases×100%.

t test and Chi-square test were used for comparing the difference of measurement data and enumeration data respectively, and Ridit analysis was used for comparing the difference of clinical curative effects.Main outcome measures

Comparison of EEG and CBF of patients from two groups before and after treatment.

Comparison of post-treatment neurologic deficit of patients between two groups.ResultsAll the involved 96 patients with CI participated in the final analysis.

Clinical symptoms of patients from two groups after therapy were significantly improved as compared with those before therapy, and curative effects of early treatment group were better than those of advanced treatment group (U =1.99,P < 0.05).

After treatment, CBF in each region of brains, except for that in parietal lobe of patients in the advanced-stage treatment group, was significantly improved (P < 0.05–0.01); The improvement of CBF of patients in the early-stage treatment group was more obvious than that in the early-stage treatment group (P < 0.05–0.01).

The abnormal rate of EEF of patients from early-stage treatment group and advanced-stage treatment group before treatment was 94% and 96%, respectively. After treatment, improvement rate of EEG of patients in the early-stage treatment group was 95%, which was significantly different from that in the advanced-stage treatment group (82%,χ² =4.32,P < 0.05)ConclusionHBO therapy both at early and advanced stages of CI (within 1 week and 4 weeks after CI attack) can improve CBF and EEG of patients with early CI, especially.     

Hyperbaric oxygen therapy for cerebral blood flow and electroencephalogram in patients with acute cerebral infarction Choice for therapeutic occasion

BACKGROUND: Hyperbaric oxygen (HBO) therapy increases blood oxygen content, changes cerebral blood flow (CBF) and cerebral metabolism. Its therapeutic effects on cerebrovascular disease have been fully confirmed, but the occasion for HBO therapy is still unclear. OBJECTIVE: To observe the therapeutic effects of HBO therapy at different time on CBF and electroencephalogram (EEG) in patients with acute cerebral infarction (CI). DESIGN: Randomized controlled trial. SETTING: Department of Neurology, Shidong Hospital, Yangpu District of Shanghai. PARTICIPANTS: Ninety-six inpatients with acute CI, admitted to Department of Neurology, Shidong Hospital, Yangpu District of Shanghai from January 2001 to December 2006, were involved in this experiment. The involved participants met the diagnosis criteria of acute CI and confirmed by skull CT or MRI. They all were patients with moderate CI (16–30 points) according to neurologic deficit score formulated by Chinese Medical Association. Informed consents of detected items and therapeutic regimen were obtained from all the involved participants. They were randomized into two groups with 48 in each: early-stage treatment group and advanced-stage treatment group. Among the 48 patients in the early-stage treatment group, 21 male and 27 female, aged 53–68 years, 22 patients were found with basal ganglia infarction, 10 with brain lobe infarction, 16 with multiple infarction, 27 accompanied with hypertension and 2 accompanied with diabetes mellitus. Among the 48 patients in the advanced-stage treatment group, 23 male and 25 female, aged 52–71 years, 25 patients were found with basal ganglia infarction, 10 with brain lobe infarction, 12 with multiple infarction, 1 with brain stem infarction, 28 accompanied with hypertension and 1 accompanied with diabetes mellitus. METHODS: After admission, patients of two groups received routine drug treatment. ① Patients in the early-stage treatment group and advanced-stage treatment group began to receive HBO therapy within one week of CI and 4 weeks after CI, respectively. The total course of treatment both was 2 weeks. EEG examination was carried out before and after therapy, and CBF was determined with 133Xe inhalation. ② Assessment criteria of curative effects: Basically cured: neurologic symptoms and body signs disappeared, could work and do housework; Markedly effective: score of neurologic deficit was decreased by over 21 points, could manage himself/herself partially; Effective: score of neurologic deficit was decreased by 8 to 12 points; Non-effective: Score was increased or decreased less than 8 points, neurologic deficit was worsened, even died. Total effective rate = (number of cured+number of markedly effective+number of effective)/ number of total cases×100%. ③ t test and Chi-square test were used for comparing the difference of measurement data and enumeration data respectively, and Ridit analysis was used for comparing the difference of clinical curative effects. MAIN OUTCOME MEASURES: ① Comparison of EEG and CBF of patients from two groups before and after treatment. ② Comparison of post-treatment neurologic deficit of patients between two groups. RESULTS: All the involved 96 patients with CI participated in the final analysis. ① Clinical symptoms of patients from two groups after therapy were significantly improved as compared with those before therapy, and curative effects of early treatment group were better than those of advanced treatment group （U =1.99，P < 0.05）. ②After treatment, CBF in each region of brains, except for that in parietal lobe of patients in the advanced-stage treatment group, was significantly improved (P < 0.05–0.01); The improvement of CBF of patients in the early-stage treatment group was more obvious than that in the early-stage treatment group (P < 0.05–0.01). ③ The abnormal rate of EEF of patients from early-stage treatment group and advanced-stage treatment group before treatment was 94% and 96%, respectively. After treatment, improvement rate of EEG of patients in the early-stage treatment group was 95%, which was significantly different from that in the advanced-stage treatment group （82%，χ2 =4.32，P < 0.05） CONCLUSION: HBO therapy both at early and advanced stages of CI (within 1 week and 4 weeks after CI attack) can improve CBF and EEG of patients with early CI, especially.     

Causes and consequences of baseline cerebral blood flow reductions in Alzheimer’s disease

Reductions of baseline cerebral blood flow (CBF) of ∼10–20% are a common symptom of Alzheimer’s disease (AD) that appear early in disease progression and correlate with the severity of cognitive impairment. These CBF deficits are replicated in mouse models of AD and recent work shows that increasing baseline CBF can rapidly improve the performance of AD mice on short term memory tasks. Despite the potential role these data suggest for CBF reductions in causing cognitive symptoms and contributing to brain pathology in AD, there remains a poor understanding of the molecular and cellular mechanisms causing them. This review compiles data on CBF reductions and on the correlation of AD-related CBF deficits with disease comorbidities (e.g. cardiovascular and genetic risk factors) and outcomes (e.g. cognitive performance and brain pathology) from studies in both patients and mouse models, and discusses several potential mechanisms proposed to contribute to CBF reductions, based primarily on work in AD mouse models. Future research aimed at improving our understanding of the importance of and interplay between different mechanisms for CBF reduction, as well as at determining the role these mechanisms play in AD patients could guide the development of future therapies that target CBF reductions in AD.     

Autoregulation of cortical blood flow and oxygen tension in the rabbit

The relationship between cerebral blood flow autoregulation and oxygen tension of cerebral tissue is not fully known. We have examined the autoregulation of local cortical blood flow (CoBF) and cortical oxygen tension (bP_O2) in the rabbit.

CoBF was measured continuously by using the heated thermocouple technique and bP_O2 was monitored by the polarographic method. Intravenous injection of phenylephrine hydrochloride or trimethaphan camsylate was used to test for autoregulation by increasing or decreasing perfusion pressure. The mean values of CoBF and bP_O2 were 36±5 ml/100g/min and 32±12 mmHg respectively at 90 mmHg mean arterial blood pressure (MABP). The changes in both CoBF and bP_O2 with changing perfusion pressure were often relatively small at near baseline blood pressure and became more pronounced with large increases or decreases in MAPB. On returning from high MABP to baseline blood pressure, a hysteresis effect on CoBF was observed in 20 out of 22 cases.

The autoregulation of CoBF was maintained in the range between 80 and 100 mmHg MABP. On the other hand, bP_O2 was maintained constant in the range between 80 and 110 mmHg. This range is significantly wider than that of CoBF. We conclude that autoregulation of CoBF limits changes in local CoBF to maintain constant oxygen tension in brain tissue.     

Effect of morphine on regional cerebral oxygen consumption and supply

The effects of acute opiate receptor stimulation on regional cerebral oxygen consumptilon and blood flow were examined in 9 regions of the artificially respired, α-chloralose-anesthetized cat. Regional cerebral arterial and venous oxygen saturation were examined microspectrophotometrically and regional cerebral blood flow was monitored using radioactively tagged microspheres (15 ± 3 μm in diameter). Oxygen consumption was calculated as the product of flow and oxygen extraction. In 8 cats, after control cerebral blood flow was obtained, and in 8 experimental cats after this same measurement was obtained before and 40 min after the administration of 1.5 mg/kg morphine sulfate; the cats' heads were simultaneously sawed in 3 places and quickly frozen in liquid nitrogen-cooled propane. Systolic and diastolic blood pressure were significantly decreased by treatment. The heterogeneity of venous oxygen saturation was significantly reduced by morphine. Average cerebral blood flow, oxygen extraction and consumption were not altered significantly by morphine. Regional cerebral blood flow in the hypothalamus, thalamic oxygen extraction, and hypothalamic and thalamic oxygen consumption were significantly decreased by treatment. This low dose of morphine may produce changes in cerebral neuronal and/or synthetic activity which lowers oxygen consumption in some regions rich in opiate receptors, while not affecting overall brain oxygen supply or consumption.     

Tracking cerebral blood flow in BOLD fMRI using recursively generated regressors

BOLD functional MRI (fMRI) data are dominated by low frequency signals, many of them of unclear origin. We have recently shown that some portions of the low frequency oscillations found in BOLD fMRI are systemic signals closely related to the blood circulation (Tong et al. [2013]: NeuroImage 76:202–215). They are commonly treated as physiological noise in fMRI studies. In this study, we propose and test a novel data‐driven analytical method that uses these systemic low frequency oscillations in the BOLD signal as a tracer to follow cerebral blood flow dynamically. Our findings demonstrate that: (1) systemic oscillations pervade the BOLD signal; (2) the temporal traces evolve as the blood propagates though the brain; and, (3) they can be effectively extracted via a recursive procedure and used to derive the cerebral circulation map. Moreover, this method is independent from functional analyses, and thus allows simultaneous and independent assessment of information about cerebral blood flow to be conducted in parallel with the functional studies. In this study, the method was applied to data from the resting state scans, acquired using a multiband EPI sequence (fMRI scan with much shorter TRs), of seven healthy participants. Dynamic maps with consistent features resembling cerebral blood circulation were derived, confirming the robustness and repeatability of the method. Hum Brain Mapp 35:5471–5485, 2014. © 2014 Wiley Periodicals, Inc .     

Cerebral blood flow and metabolism following subarachnoid haemorrhage: cerebral oxygen uptake and global blood flow during the acute period in patients with SAH

Forty-eight patients with subarachnoid haemorrhage were studied with repeated rCBF and CMRO2 measurements. Cortical rCBF was measured using xenon-inhalation technique. CMRO2 was calculated as AVDO2 x CBF. When first studied the 29 conscious patients showed relative hyperaemia with CBF at 50 ml and reduced CMRO2 at 2.17 ml. In the following week CBF decreased to 41. CMRO2 remained reduced and constant. The 19 unconscious patients showed initially pronounced reduction in CMRO2 to 1.26, followed by gradual increase to 1.73 in 4-5 days. Simultaneously CBF increased from 18 ml to slightly above 30 ml. In the conscious patients the early reduction in CMRO2 and the concomitant luxury perfusion may be explained by global ischaemia because of very high ICP at the time of the haemorrhage. The reduced CBF in the unconscious group could be due to increased ICP, as ventricular drainage increased CBF to levels of relative hyperaemia as demonstrated in one case. As no decrease in CMRO2 was seen during the first 2 weeks, it is suggested that ischaemia at the time of aneurysm rupture is the most important single factor in reduction of global CMRO2.     

Pseudocontinuous arterial spin labeling reveals dissociable effects of morphine and alcohol on regional cerebral blood flow

We have examined sensitivity and specificity of pseudocontinuous arterial spin labeling (PCASL) to detect global and regional changes in cerebral blood flow (CBF) in response to two different psychoactive drugs. We tested alcohol and morphine in a placebo-controlled, double-blind randomized study in 12 healthy young men. Drugs were administered intravenously. Validated pharmacokinetic protocols achieved minimal intersubject and intrasubject variance in plasma drug concentration. Permutation-based statistical testing of a mixed effect repeated measures model revealed a widespread increase in absolute CBF because of both morphine and alcohol. Conjunction analysis revealed overlapping effects of morphine and alcohol on absolute CBF in the left anterior cingulate, right hippocampus, right insula, and left primary sensorimotor areas. Effects of morphine and alcohol on relative CBF (obtained from z-normalization of absolute CBF maps) were significantly different in the left putamen, left frontoparietal network, cerebellum, and the brainstem. Corroborating previous PET results, our findings suggest that PCASL is a promising tool for central nervous system drug research.     

Redistribution of blood flow in the cerebral cortex of normal subjects during head-up postural change

Regional cerebral blood flow was measured in 21 normotensive subjects during supine rest and during head-up tilt to 70°. The results showed significant and consistent regional cerebral blood flow changes in the frontal areas with lower relative flow distribution values (percentage of mean flow) during head-up tilt than during supine rest. The lower frontal flow distribution values during tilt were not related to habituation, to repeated measurements, or to the estimated level of arterial CO₂ which was derived from expired end-tidal CO₂ levels. None of the subjects had orthostatic hypotension and there was no significant difference in mean hemispheric blood flow between lying down and standing up. There was no significant gender difference in regional cerebral blood flow, although female subjects tended to have higher mean hemispheric flow than males in both postures. It remains to be established whether the flow decreases in the frontal cortex are caused by cerebral functional factors or by haemodynamic mechanisms.     

抑郁症患者局部脑血流灌注变化研究

目的 分析抑郁症患者单光子发射型计算机断层显像(SPECT)局部脑血流(SCBF)灌注变化的特点,并初步探讨rCBF显像在抑郁症患者中的诊断价值. 方法 对10例正常人及临床诊断为抑郁症的32例患者分别进行SPECT局部脑血流灌注显像,利用感兴趣区(ROI)法观察rCBF情况;11例患者同期行MRI普通扫描.结果 32例抑郁症患者中31例发现rCBF显像异常,共检出71个病灶,分别位于双侧额叶、颞叶、基底节、海马、扣带回及左侧岛叶,其中57个病灶位于颞叶、海马、扣带回及岛叶,即边缘系统,9个病灶位于额叶,5个病灶位于基底节;基底节区病灶局部脑血流灌注均增高,其他部位病灶均降低;双侧大脑半球rCBF病灶构成比差异无统计学意义(χ~2=409,P=0.790).11例患者同期做MRI扫描,3例发现异常(2例轻度脑萎缩,1例海马萎缩),而此11例患者rCBF显像均发现异常.1例正常人rCBF未发现异常显像.结论 大多数抑郁症患者存在脑边缘系统rCBF降低,部分患者存在基底节区rCBF增高.SPECT能敏感地发现抑郁症患者rCBF灌注的变化,对抑郁症的诊断具有一定的价值.     

磁共振相位对比血管成像测量脑血流量的最佳速度编码

实验运用1.5-T磁共振的2D cine PC序列对10位健康志愿者C2水平感兴趣区血管进行速度编码为30~90cm/s,间隔10cm/s的7次同层扫描,探讨速度编码在磁共振相位对比血管成像中对测量脑血流量及入脑/出脑血流的影响。发现不同的速度编码对颈内动脉血流量、最大血流速度和平均血流速度影响较大,对椎动脉及颈内静脉影响不明显。当速度编码为60～80cm/s时,入脑血流量为(655±118)mL/min,出脑血流量(506±186)mL/min,入脑血流量/出脑血流量稳定在0.78～0.83,且所有血管中无混淆现象。提示在应用磁共振相位增强血管成像测量脑血流量时,应选择60～80cm/s的速度编码。