Mean Global Cerebral Blood Flow Research Articles

Decrease in Cerebral Blood Flow after Reoxygenation Is Associated with Neurological Syndrome Sequelae and Blood Pressure.

Changes in cerebral blood flow (CBF) and regulation of cerebral circulation occur at high altitude (HA). However, the changes in CBF and their associations with neurological syndrome sequelae and blood pressure after subjects return to the lowlands remain unclear. In this study, the subjects were 23 college students who were teaching at an altitude of 4300 m for 30 days. These subjects were studied before reaching the HA (Test 1), one week after returning to the lowlands (Test 2), and three months after returning to the lowlands (Test 3). Symptom scores for de-acclimatization syndrome were evaluated. Changes in CBF were measured using the magnetic resonance imaging arterial spin labeling (ASL) technique. Additionally, the velocity of CBF in the cerebral arteries was measured using a transcranial doppler (TCD). In Test 2 vs. Test 1, the peak systolic velocity and mean velocity in the basilar artery were significantly decreased. CBF exhibited significant decreases in the left putamen/cerebellum crus1/vermis and right thalamus/inferior temporal gyrus, while significant increases were observed in the left postcentral gyrus/precuneus and right middle cingulate gyrus/superior frontal gyrus. In Test 3 vs. Test 1, the basilar artery velocity returned to the baseline level, while CBF continued to decrease. The mean global CBF showed a decreasing trend from Test 1 to Test 3. Furthermore, the mean global CBF had a negative correlation with the systolic pressure, pulse pressure, and mean arterial pressure. The decrease in CBF after reoxygenation may underlie the neurological symptoms in subjects returning to the lowlands. Increased blood pressure could serve as a predictor of a decrease in CBF.

Arterial Spin Labeling Reveals Elevated Cerebral Blood Flow with Distinct Clusters of Hypo- and Hyperperfusion after Traumatic Brain Injury.

Imaging detection of brain perfusion alterations after traumatic brain injury (TBI) may provide prognostic insights. In this study, we used arterial spin labeling (ASL) to quantify cross-sectional and longitudinal changes in cerebral blood flow (CBF) after TBI and correlated changes with clinical outcome. We analyzed magnetic resonance imaging scans from adult participants with TBI requiring hospitalization in the acute (2 weeks post-injury, n = 33) and chronic (6 months post-injury, n = 16) phases, with 13 participants scanned longitudinally at both time points. We also analyzed 18 age- and sex-matched healthy controls. Whole-brain CBF maps were derived using a three-dimensional pseudo-continuous arterial spin label technique. Mean CBF across tissue-based regions (whole brain, gray matter, and white matter) was compared cross-sectionally and longitudinally. In addition, individual-level clusters of abnormal perfusion were identified using voxel-based z-score analysis of relative CBF maps, and number and volume of abnormally hypo- and hyperperfused clusters were assessed cross-sectionally and longitudinally. Finally, all CBF measures were correlated with clinical outcome measures. Mean global and gray matter CBF were significantly elevated in acute and chronic TBI participants compared to controls. Participants with better outcome at 6 months post-injury tended to have higher CBF in the acute phase compared to those with poorer outcome. Acute TBI participants had a significantly greater volume of hypo- and hyperperfused brain tissue compared to controls, with these regions partially normalizing by the chronic phase. Our findings demonstrate global elevation of CBF with focal hypo- and hyperperfusion in the early post-injury period and suggest a reparative role for acute elevation in CBF post-TBI.

Assessment of regional cerebral blood flow by ct perfusion in patients of Alzheimer’s disease

Background: Alzheimer’s disease is a neurodegenerative disorder and is characterized by progressive cognitive decline which starts with an impairment in the ability to recollect recent memories, but eventually affects all the intellectual functions and finally leads to a total dependence for basic functions of daily life culminating into premature death. Dementia can be defined as a clinical syndrome characterized by a cluster of symptoms and signs manifested by difficulties in memory, disturbances in language and other cognitive functions, changes in behavior, and impairments in activities of daily living. Alzheimer is an age-associated degenerative disorder. The burden of Alzheimer’s disease and that of dementia per se is dependent on age. With increasing life expectancy, the proportion of elderly is increasing and so is the number of patients with Alzheimer’s disease associated dementia. Material and Method: This cross-sectional study was carried out for duration of 18 months at Department of Radiodiagnosis, Era's Lucknow Medical College, Lucknow with an aim to study the parameters viz. cerebral blood flow and cerebral blood volume and to correlate the finding of CT perfusion with the clinical score of dementia. The Patients attending adult psychiatry OPD diagnosed as a case of Alzheimer's as per DSM 4 criteria by fulfilling the inclusion criteria and giving informed consent were taken up for study. They were also evaluated for socio-demographic details and illness related variables. After obtaining an informed consent, demographic information, duration and nature of complaints was noted. All the patients were then subjected to CT Perfusion evaluation. Dementia severity was assessed using Clinical Dementia Rating Scale (CDRS).Result: Age of patients ranged from 60 to 75 years with a mean of 66±4.03 years. Majority of cases were aged between 60 and 69 years (77.5%). There were only 9 patients aged >70 years (22.5%).Forgetfulness (40%), difficulty in thinking (27.5%) and mental confusion (27.5%) were the three most common presenting complaints followed by loneliness (22.5%), agitation (17.5%), depression and mental decline (15% each). Inability to recognize (10%) and hallucinations (7.5%) were among the least common presenting complaints. According to clinical dementia score, a total of 16 (40%) patients were categorized as mild dementia, 20 (50%) as moderate dementia and 4 (10%) as severe dementia respectively. Mean regional cerebral blood flow values for right frontal, left frontal, left temporal, right occipital, right lenticular nucleus and left lenticular nucleus were 39.46±3.82, 39.33±3.87, 45.59±4.66, 45.51±5.02, 45.59±4.76, 45.65±4.49, 42.57±4.23 and 42.87±4.81 ml/100 g/min respectively. Mean global CBF was calculated as 43.32±4.29 ml/100 g/min. Mean regional cerebral blood volume values for right frontal, left frontal, left temporal, right occipital, right lenticular nucleus and left lenticular nucleus were 2.56±0.49, 2.62±0.54, 2.97±0.50, 3.03±0.56, 2.95±0.48, 2.92±0.52, 3.13±0.55 and 3.13±0.55 ml/100 g respectively. Mean global CBF was calculated as 2.91±0.49 ml/100 g/min.Conclusion: A total of 40 patients of Alzheimer’s disease aged 60 to 75 years (Mean age 66±4.03 years; 65% males) were enrolled and subjected to clinical and CT evaluation. According to clinical dementia score, a total of 16 (40%) patients were categorized as mild dementia, 20 (50%) as moderate dementia and 4 (10%) as severe dementia respectively. Mean cerebral blood flow (CBF) ranged from 39.33±3.87 ml/100 g/min (Left frontal region) to 45.65±4.49 ml/100 g/min (Left occipital region) among different brain regions. Mean global CBF was 43.32±4.29 ml/100 g/min.

Cerebrovascular effects of glibenclamide investigated using high-resolution magnetic resonance imaging in healthy volunteers

Glibenclamide inhibits sulfonylurea receptor (SUR), which regulates several ion channels including SUR1-transient receptor potential melastatin 4 (SUR1-TRPM4) channel and ATP-sensitive potassium (KATP) channel. Stroke upregulates SURl-TRPM4 channel, which causes a rapid edema formation and brain swelling. Glibenclamide may antagonize the formation of cerebral edema during stroke. Preclinical studies showed that glibenclamide inhibits KATP channel-induced vasodilation without altering the basal vascular tone. The in vivo human cerebrovascular effects of glibenclamide have not previously been investigated. In a randomized, double-blind, placebo-controlled, three-way cross-over study, we used advanced 3 T MRI methods to investigate the effects of glibenclamide and KATP channel opener levcromakalim on mean global cerebral blood flow (CBF) and intra- and extracranial artery circumferences in 15 healthy volunteers. Glibenclamide administration did not alter the mean global CBF and the basal vascular tone. Following levcromakalim infusion, we observed a 14% increase of the mean global CBF and an 8% increase of middle cerebral artery (MCA) circumference, and glibenclamide did not attenuate levcromakalim-induced vascular changes. Collectively, the findings demonstrate the vital role of KATP channels in cerebrovascular hemodynamic and indicate that glibenclamide does not inhibit the protective effects of KATP channel activation during hypoxia and ischemia-induced brain injury.

Quantitative cerebral blood flow using xenon-enhanced CT after decompressive craniectomy in traumatic brain injury.

OBJECTIVE Few studies have reported on changes in quantitative cerebral blood flow (CBF) after decompressive craniectomy and the impact of these measures on clinical outcome. The aim of the present study was to evaluate global and regional CBF patterns in relation to cerebral hemodynamic parameters in patients after decompressive craniectomy for traumatic brain injury (TBI). METHODS The authors studied clinical and imaging data of patients who underwent xenon-enhanced CT (XeCT) CBF studies after decompressive craniectomy for evacuation of a mass lesion and/or to relieve intractable intracranial hypertension. Cerebral hemodynamic parameters prior to decompressive craniectomy and at the time of the XeCT CBF study were recorded. Global and regional CBF after decompressive craniectomy was measured using XeCT. Regional cortical CBF was measured under the craniectomy defect as well as for each cerebral hemisphere. Associations between CBF, cerebral hemodynamics, and early clinical outcome were assessed. RESULTS Twenty-seven patients were included in this study. The majority of patients (88.9%) had an initial Glasgow Coma Scale score ≤ 8. The median time between injury and decompressive surgery was 9 hours. Primary decompressive surgery (within 24 hours) was performed in the majority of patients (n = 18, 66.7%). Six patients had died by the time of discharge. XeCT CBF studies were performed a median of 51 hours after decompressive surgery. The mean global CBF after decompressive craniectomy was 49.9 ± 21.3 ml/100 g/min. The mean cortical CBF under the craniectomy defect was 46.0 ± 21.7 ml/100 g/min. Patients who were dead at discharge had significantly lower postcraniectomy CBF under the craniectomy defect (30.1 ± 22.9 vs 50.6 ± 19.6 ml/100 g/min; p = 0.039). These patients also had lower global CBF (36.7 ± 23.4 vs 53.7 ± 19.7 ml/100 g/min; p = 0.09), as well as lower CBF for the ipsilateral (33.3 ± 27.2 vs 51.8 ± 19.7 ml/100 g/min; p = 0.07) and contralateral (36.7 ± 19.2 vs 55.2 ± 21.9 ml/100 g/min; p = 0.08) hemispheres, but these differences were not statistically significant. The patients who died also had significantly lower cerebral perfusion pressure (52 ± 17.4 vs 75.3 ± 10.9 mm Hg; p = 0.001). CONCLUSIONS In the presence of global hypoperfusion, regional cerebral hypoperfusion under the craniectomy defect is associated with early mortality in patients with TBI. Further study is needed to determine the value of incorporating CBF studies into clinical decision making for severe traumatic brain injury.

Noninvasive Measurement of Cerebral Blood Flow Under Anesthesia Using Arterial Spin Labeling MRI: A Pilot Study.

Cerebral ischemia plays a major role in pathophysiology of the injured brain. Most of the currently available methods of cerebral blood flow (CBF) monitors are either indirect measure of CBF or needing radioactive agents for data acquisition. Arterial spin labeling magnetic resonance imaging (ASL-MRI) is a noninvasive method of measuring CBF. The aim of our study was to determine the differences in the CBF values between propofol and sevoflurane anesthesia using ASL-MRI technique in mechanically ventilated patients with cerebrovascular disease. After ethics board approval and informed consent, we measured CBF in 4 patients with moyamoya disease, using a pseudo-continuous 3D ASL sequence available on a 3.0 T MRI scanner. Patients were anesthetized first with sevoflurane (1 MAC) and then anesthesia was converted to total intravenous anesthesia with propofol (100 to 125 μg/kg/min). When the patient was in a steady state with respect to anesthesia and normocapnia (baseline PETCO2), CBF was measured under both sevoflurane and propofol anesthesia. Quantitative estimation of both global and regional CBF was successfully performed in all patients. The mean global CBF in gray and white matter of all patients under propofol anesthesia were 38.4 and 31.6 mL/100 g/min, respectively. Similar values under sevoflurane anesthesia were 56.6 mL/100 g/min for gray matter and 42.5 mL/100 g/min for white matter. ASL-MRI is a feasible, noninvasive method of quantitative estimation of global and regional CBF in mechanically ventilated patients under anesthesia. In this pilot study CBF was consistently greater with sevoflurane than with propofol.

Cerebral blood flow and metabolism during mild hypothermia in patients with severe traumatic brain injury.

Cerebral blood flow (CBF) measurements during mild hypothermia therapy were made in 30 adult patients with severe head injuries (Glasgow Coma Scale score < or =18), by xenon enhanced computed tomography (Xe-CT). All patients but one underwent removal of hematomas and decompressive craniectomy. Immediately after surgery, hypothermia was induced by surface cooling, and a brain temperature of 32-35 degrees C was maintained for 3 days. During hypothermia therapy, CBF measurements by Xe-CT were made for all patients on post-injury days 1 to 4. From the arteriovenous-oxygen content difference and CBF values, the cerebral metabolic rate of oxygen (CMRO2) values were obtained. Outcome was assessed at discharge according to the patients' Glasgow Outcome Scale (GOS) scores. Patients were divided into two groups based on their outcomes. Nineteen patients (63%) showed good outcomes (GOS score of 4 or 5) and 11 (37%) showed poor outcomes (GOS score of 1, 2, or 3). Statistically significant differences were obtained for the mean global CBF and CMRO2 values between the good and poor outcome groups. In this study, we demonstrated that CBF measurement may be useful to predict neurological outcomes following severe traumatic brain injury in patients undergoing hypothermia as well as to identify those who might not likely benefit from hypothermia therapy.

Comparison of global cerebral blood flow measured by phase‐contrast mapping MRI with 15O‐H2O positron emission tomography

PurposeTo compare mean global cerebral blood flow (CBF) measured by phase‐contrast mapping magnetic resonance imaging (PCM MRI) and by 15O‐H2O positron emission tomography (PET) in healthy subjects. PCM MRI is increasingly being used to measure mean global CBF, but has not been validated in vivo against an accepted reference technique.Materials and MethodsSame‐day measurements of CBF by 15O‐H2O PET and subsequently by PCM MRI were performed on 22 healthy young male volunteers. Global CBF by PET was determined by applying a one‐tissue compartment model with measurement of the arterial input function. Flow was measured in the internal carotid and vertebral arteries by a noncardiac triggered PCM MRI sequence at 3T. The measured flow was normalized to total brain weight determined from a volume‐segmented 3D T 1‐weighted anatomical MR‐scan.ResultsMean CBF was 34.9 ± 3.4 mL/100 g/min measured by 15O‐H2O PET and 57.0 ± 6.8 mL/100 g/min measured by PCM MRI. The measurements were highly correlated (P = 0.0008, R2 = 0.44), although values obtained by PCM MRI were higher compared to 15O‐H2O PET (absolute and relative differences were 22.0 ± 5.2 mL/100 g/min and 63.4 ± 14.8%, respectively).ConclusionThis study confirms the use of PCM MRI for quantification of global CBF, but also that PCM MRI systematically yields higher values relative to 15O‐H2O PET, probably related to methodological bias. Level of Evidence: 3J. Magn. Reson. Imaging 2017;45:692–699.

Cerebral blood flow in small vessel disease: A systematic review and meta-analysis

White matter hyperintensities are frequent on neuroimaging of older people and are a key feature of cerebral small vessel disease. They are commonly attributed to chronic hypoperfusion, although whether low cerebral blood flow is cause or effect is unclear. We systematically reviewed studies that assessed cerebral blood flow in small vessel disease patients, performed meta-analysis and sensitivity analysis of potential confounders. Thirty-eight studies (n = 4006) met the inclusion criteria, including four longitudinal and 34 cross-sectional studies. Most cerebral blood flow data were from grey matter. Twenty-four cross-sectional studies (n = 1161) were meta-analysed, showing that cerebral blood flow was lower in subjects with more white matter hyperintensity, globally and in most grey and white matter regions (e.g. mean global cerebral blood flow: standardised mean difference−0.71, 95% CI −1.12, −0.30). These cerebral blood flow differences were attenuated by excluding studies in dementia or that lacked age-matching. Four longitudinal studies (n = 1079) gave differing results, e.g., more baseline white matter hyperintensity predated falling cerebral blood flow (3.9 years, n = 575); cerebral blood flow was low in regions that developed white matter hyperintensity (1.5 years, n = 40). Cerebral blood flow is lower in subjects with more white matter hyperintensity cross-sectionally, but evidence for falling cerebral blood flow predating increasing white matter hyperintensity is conflicting. Future studies should be longitudinal, obtain more white matter data, use better age-correction and stratify by clinical diagnosis.

Preliminary Investigation of Cerebral Blood Flow and Amyloid Burden in Veterans With and Without Combat-Related Traumatic Brain Injury

This study aimed to examine global and regional cerebral blood flow and amyloid burden in combat veterans with and without traumatic brain injury (TBI). Cerebral blood flow (in milliliters per minute per 100 mL) was measured by quantitative [(15)O]water, and amyloid burden was measured by [(11)C]PIB imaging. Mean global cerebral blood flow was significantly lower in veterans with TBI compared with non-TBI veterans. There were essentially no differences between groups for globally normalized regional cerebral blood flow. Amyloid burden did not differ between TBI and non-TBI veterans. Veterans who have suffered a TBI have significantly lower cerebral blood flow than non-TBI controls but did not manifest increased levels of amyloid, globally or regionally.

Relationship Between Cardiac Dysfunction and Cerebral Perfusion in Patients with Aneurysmal Subarachnoid Hemorrhage

Cardiac dysfunction may occur after aneurysmal subarachnoid hemorrhage (aSAH). Although it is associated with poor outcome, the pathophysiological mechanism of this association remains unclear. We investigated the relationship between cardiac function and cerebral perfusion in patients with aSAH. We studied 72 aSAH patients admitted within 72 h after ictus with echocardiography and cerebral CT perfusion within 24 h after admission. Cardiac dysfunction was defined as myocardial wall motion abnormalities or positive troponin. In patients with and without cardiac dysfunction, we calculated the mean perfusion [cerebral blood flow (CBF) and time-to-peak (TTP)] in standard regions of interest and calculated differences with 95% confidence intervals (95% CI). In 35 patients with cardiac dysfunction minimal CBF was 15.83 mL/100 g/min compared to 18.59 in 37 without (difference of means -2.76; 95% CI -5.43 to -0.09). Maximal TTP was 26.94 s for patients with and 23.10 s for patients without cardiac dysfunction (difference of means 3.84; 95% CI 1.63-6.05). Mean global CBF was 21.71 mL/100 g/min for patients with cardiac dysfunction and 24.67 mL/100 g/min for patients without cardiac dysfunction (-2.96; 95% CI -6.19 to 0.27). Mean global TTP was 25.27 s for patients with cardiac dysfunction and 21.26 for patients without cardiac dysfunction (4.01; 95% CI 1.95-6.07). aSAH patients with cardiac dysfunction have decreased focal and global cerebral perfusion. Further studies should evaluate whether this relation is explained by a direct effect of cardiac dysfunction on cerebral circulation or by an external determinant, such as a hypercatecholaminergic or hypometabolic state, influencing both cardiac function and cerebral perfusion.

Positron emission tomography/magnetic resonance hybrid scanner imaging of cerebral blood flow using (15)O-water positron emission tomography and arterial spin labeling magnetic resonance imaging in newborn piglets.

Abnormality in cerebral blood flow (CBF) distribution can lead to hypoxic–ischemic cerebral damage in newborn infants. The aim of the study was to investigate minimally invasive approaches to measure CBF by comparing simultaneous 15O-water positron emission tomography (PET) and single TI pulsed arterial spin labeling (ASL) magnetic resonance imaging (MR) on a hybrid PET/MR in seven newborn piglets. Positron emission tomography was performed with IV injections of 20 MBq and 100 MBq 15O-water to confirm CBF reliability at low activity. Cerebral blood flow was quantified using a one-tissue-compartment-model using two input functions: an arterial input function (AIF) or an image-derived input function (IDIF). The mean global CBF (95% CI) PET-AIF, PET-IDIF, and ASL at baseline were 27 (23; 32), 34 (31; 37), and 27 (22; 32) mL/100 g per minute, respectively. At acetazolamide stimulus, PET-AIF, PET-IDIF, and ASL were 64 (55; 74), 76 (70; 83) and 79 (67; 92) mL/100 g per minute, respectively. At baseline, differences between PET-AIF, PET-IDIF, and ASL were 22% (P<0.0001) and −0.7% (P=0.9). At acetazolamide, differences between PET-AIF, PET-IDIF, and ASL were 19% (P=0.001) and 24% (P=0.0003). In conclusion, PET-IDIF overestimated CBF. Injected activity of 20 MBq 15O-water had acceptable concordance with 100 MBq, without compromising image quality. Single TI ASL was questionable for regional CBF measurements. Global ASL CBF and PET CBF were congruent during baseline but not during hyperperfusion.

Abstract T P370: Blood Transfusions in Pediatric Sickle Cell Disease Normalize Cerebral Blood Flow While Maintaining Constant Cerebral Oxygen Metabolism

Background: Chronic blood transfusions (Tx) reduces stroke risk in pediatric sickle cell disease (SCD). Cerebral blood flow (CBF) is elevated in SCD, likely representing a compensatory mechanism to maintain cerebral oxygen metabolism (CMRO2) in the setting of reduced arterial oxygen content (CaO2) from chronic anemia. When exhausted compensatory mechanisms are unable to meet oxygen demands, stroke ensues. We measured MR-derived CBF and oxygen extraction fraction (OEF) pre- and post-Tx, hypothesizing that Tx ‘resets’ the CBF baseline by increasing CaO2 via increased hemoglobin (Hb), while maintaining cerebral oxygen delivery and metabolism. Methods: SCD children on chronic Tx were enrolled in a prospective, observational MRI study. MR-CBF and MR-OEF were acquired before and 2 hours after exchange Tx. MR-CBF and MR-OEF were measured using pseudocontinuous arterial spin labelling and a novel asymmetric spin echo sequence, respectively. CaO2 =1.35 x [Hb] x SaO2. CMRO2 = CaO2 x CBF x OEF. Results: Two SCD children underwent MRI pre- and post-Tx (six more are anticipated prior to ISC). For subject #1 (18 yo F with overt stroke), mean global CBF was 128 and 98 ml/min/100g pre- and post-Tx, respectively, indicating a 24% CBF reduction. For subject #2 (6 yo F with elevated transcranial Doppler velocities), mean global CBF was 189 and 129 ml/min/100g pre- and post-Tx, respectively, a 32% CBF reduction (Fig). Both Hb and CaO2 were increased after Tx, resulting in unchanged oxygen delivery (CaO2 x CBF) post-Tx. Moreover, OEF and CMRO2 were not significantly different pre- and post-Tx, consistent with our hypothesis that CBF increases to maintain oxygen delivery. Conclusions: Elevated CBF is likely a compensatory mechanism to maintain constant oxygen delivery in SCD children who have chronically low CaO2. In our subjects, Tx improved CaO2, allowing CBF to normalize. This reduced hemodynamic stress likely contributes to the lower stroke risk in chronically transfused SCD children.

Thirty minute transcutaneous electric acupoint stimulation modulates resting state brain activities: A perfusion and BOLD fMRI study

Increasing neuroimaging studies have focused on the sustained after effects of acupuncture, especially for the changes of brain activities in rest. However, short-period stimuli have mostly been chosen in these works. The present study aimed to investigate how the resting state brain activities in healthy subjects were modulated by relatively long-period (30min) acupuncture, a widely used modality in clinical practice. Transcutaneous electric acupoint stimulation (TEAS) or intermittent minimal TEAS (MTEAS) were given for 30min to 40 subjects. Functional MRI (fMRI) data were collected including the pre-stimulation resting state and the post-stimulation resting state, using dual-echo arterial spin labeling (ASL) techniques, representing both cerebral blood flow (CBF) signals and blood oxygen-dependent level (BOLD) signals simultaneously. Following 30min TEAS, but not MTEAS, the mean global CBF decreased, and a significant decrease of regional CBF was observed in SI, insula, STG, MOG and IFG. Functional connectivity analysis showed more secure and spatially extended connectivity of both the DMN and SMN after 30min TEAS. Our results implied that modulation of the regional brain activities and network connectivity induced by thirty minute TEAS may associate with the acupuncture-related therapeutic effects. Furthermore, the resting state regional CBF quantified by ASL perfusion fMRI may serve as a potential biomarker in future acupuncture studies.

Mean cerebral blood flow measurements using phase contrast MRI in the first year of life

Alterations in cerebral blood flow (CBF) are believed to be linked to many of the neurological pathologies that affect neonates and small infants. CBF measurements are nonetheless often difficult to perform in this population, as many techniques rely on radioactive tracers or other invasive methods. In this study, mean global CBF was measured in 21 infants under the age of one, using non-invasive MRI techniques adapted to the neonatal population. Mean CBF was computed as the ratio of blood flow delivered to the brain (measured using phase contrast MRI) and brain volume (computed by segmenting anatomical MR images). Tests in adult volunteers and repeated measurements showed the flow measurements using the proposed method to be both accurate and reproducible. It was also found that cardiac gating need not be employed in infants with no known cardiac pathology. The developed technique can easily be appended to a neonatal MRI examination to provide rapid, robust, and non-invasive estimates of mean CBF, thus providing a means to monitor developmental or pathology-related alterations in cerebral perfusion and the impact of different treatment courses. In the imaged cohort, mean CBF and flow to the brain were found to rapidly increase during the first year of life (from approx. 25 to 60 ml blood/100 ml tissue/min), in good agreement with literature from other modalities where available. Mean CBF also showed a significant correlation with arterial oxygen saturation level and heart rate, but no significant correlation was found between CBF and the hematocrit or body temperature.

IC-P1-001: Volume reduction in cerebral blood flow in patients with Alzheimer's disease: A sonographic study

Alzheimer disease (AD) is characterised by progressive impairment of memory and cognitive function. PET and SPECT, in previous studies, demonstrated consistent reduction of cerebral blood flow (CBF) in AD. Recently, reports have described the use of sonographic techniques in estimating CBF by measuring flow volumes of the extracranial carotid and vertebral arteries in healthy adults. Ultrasound techniques are more diffused than other procedures, less expensive, and the absence of adverse effects allows repeated examinations without risk for the patients. Fifty patients who met the diagnostic criteria of probable AD (NINDS-ADRDA)) were compared to 50 age matched healthy elderly volunteers. The extracranial internal carotid arteries and the vertebral arteries of the patients and controls were examined. Angle corrected time averaged flow velocity (TAV) and the diameter of the vessel were measured. Intravascular flow volumes were calculated as the product of TAV and the cross-sectional area of the circular vessel. CBF volume was calculated as the sum of flow volumes in the internal carotid and vertebral arteries of both sides. All subjects underwent MMSE. The mean global CBF (474.87 ± 94.085 vs 744.26 ± 94.082 mL/min; p<0.0001) was lower in AD patients than in healthy volunteers. A significant decline in global flow volumes (r=0.48; p<0.0007) with degree of cognitive impairment was also present. The significance of the present study is a statistically demonstration of cerebral blood flow deficits in Alzheimer's disease using a non-invasive method. The global cerebral blood flow reduction is particularly prominent, as expected, and even more so in the more severe affected patients. Cerebral blood reduction is independent from vascular risk factors and may be due to cerebral vasoconstriction and decreased cerebral demand. Furthermore, color duplex flowmetry of the cervical arteries offers us an additional tool for the investigation of brain circulation and highlights several important characteristics of CBF in AD. In contrast to other neuroimaging techniques, the procedure may be performed and repeated at anytime and since it is not invasive and not expensive, it may be used for monitoring CBF in AD as well as for research on pharmacological factors affecting CBF.

Cerebral Blood Flow by Using Pulsed Arterial Spin-Labeling in Elderly Subjects with White Matter Hyperintensities

On MR imaging, white matter hyperintensities (WMH) on T2-weighted images are generally considered as a surrogate marker of ischemic small vessel disease in elderly subjects. Pulsed arterial spin-labeling (PASL) is a noninvasive MR perfusion-weighted technique. We hypothesized that elderly subjects with diffuse confluent WMH should have lower cerebral blood flow (CBF) measurements than subjects with punctiform or beginning confluent WMH. MR images of 21 subjects (13 women; mean age, 76 years; SD, 5), stratified for the degree of WMH, from a single center within the multinational Leukoaraiosis and Disability (LADIS) study, were investigated. CBF images were obtained by means of quantitative imaging of perfusion by using a single-subtraction second version, with thin-section TI periodic saturation PASL. Values of cortical gray matter, subcortical (including white matter and deep gray matter), and global CBF were calculated. CBF measurements of subjects with diffuse confluent WMH (n = 7) were compared with those of subjects with punctiform or beginning confluent WMH (n = 14). Subjects with diffuse confluent WMH were found to have approximately 20% lower mean global CBF (43.5 mL/100 mL/min; SD, 6.3) than subjects with punctiform or beginning confluent WMH (57.9 mL/100 mL/min; SD, 8.6; P < .01), as well as approximately 20% lower mean subcortical (P < .01) and cortical gray matter CBF (P < .05). PASL revealed a significant reduction of CBF measurements in elderly subjects with diffuse confluent WMH.

Gray matter blood flow change is unevenly distributed during moderate isocapnic hypoxia in humans

Hypoxia increases cerebral blood flow (CBF), but it is unknown whether this increase is uniform across all brain regions. We used H(2)(15)O positron emission tomography imaging to measure absolute blood flow in 50 regions of interest across the human brain (n = 5) during normoxia and moderate hypoxia. Pco(2) was kept constant ( approximately 44 Torr) throughout the study to avoid decreases in CBF associated with the hypocapnia that normally occurs with hypoxia. Breathing was controlled by mechanical ventilation. During hypoxia (inspired Po(2) = 70 Torr), mean end-tidal Po(2) fell to 45 +/- 6.3 Torr (means +/- SD). Mean global CBF increased from normoxic levels of 0.39 +/- 0.13 to 0.45 +/- 0.13 ml/g during hypoxia. Increases in regional CBF were not uniform and ranged from 9.9 +/- 8.6% in the occipital lobe to 28.9 +/- 10.3% in the nucleus accumbens. Regions of interest that were better perfused during normoxia generally showed a greater regional CBF response. Phylogenetically older regions of the brain tended to show larger vascular responses to hypoxia than evolutionary younger regions, e.g., the putamen, brain stem, thalamus, caudate nucleus, nucleus accumbens, and pallidum received greater than average increases in blood flow, while cortical regions generally received below average increases. The heterogeneous blood flow distribution during hypoxia may serve to protect regions of the brain with essential homeostatic roles. This may be relevant to conditions such as altitude, breath-hold diving, and obstructive sleep apnea, and may have implications for functional brain imaging studies that involve hypoxia.

A PET study of regional cerebral blood flow after experimental cardiopulmonary resuscitation

Cerebral blood flow (CBF) during cardiopulmonary resuscitation and after restoration of spontaneous circulation (ROSC) from cardiac arrest has previously been measured with the microspheres and laser Doppler techniques. We used positron emission tomography (PET) with [15O]--water to map the haemodynamic changes after ROSC in nine young pigs. After the baseline PET recording, ventricular fibrillation of 5 min duration was induced, followed by closed-chest cardiopulmonary resuscitation (CPR) in conjunction with IV administration of three bolus doses of adrenaline (epinephrine). After CPR, external defibrillatory shocks were applied to achieve ROSC. CBF was measured at intervals during 4h after ROSC. Relative to the mean global CBF at baseline (32+/-5 ml hg(-1)min(-1)), there was a substantial global increase in CBF at 10 min, especially in the diencephalon. This was followed by an interval of cortical hypoperfusion and a subsequent gradual return to baseline values.

Volume Reduction in Cerebral Blood Flow in Patients with Alzheimer’s Disease: A Sonographic Study

Neuroimaging techniques such as PET and SPECT demonstrated a consistent reduction of cerebral blood flow (CBF) in Alzheimer’s disease (AD). The aim of the study was to assess the potential role of ultrasonography for CBF measurement in AD patients and whether the CBF volume correlates positively with disease severity. Fifty patients who met the diagnostic criteria of probable AD (NINDS-ADRDA) were compared to 50 age-matched healthy elderly volunteers. The extracranial internal carotid arteries (ICAs) and the vertebral arteries (VAs) of the patients and controls were examined. Angle-corrected time-averaged flow velocity (TAV) and the diameter of the vessel were measured. Intravascular flow volumes were calculated as the product of TAV and the cross-sectional area of the circular vessel. CBF volume was calculated as the sum of flow volumes in the ICAs and VAs of both sides. All subjects underwent the MMSE. The mean global CBF (474.87 ± 94.085 vs. 744.26 ± 94.082 ml/min; p < 0.0001) was lower in AD patients than in healthy volunteers. A significant decline in global flow volumes (r = 0.48; p < 0.0007) with the degree of cognitive impairment was also present. The ability of ultrasonography to characterize flow decreases makes such a technique an attractive tool for the study of AD, for the evaluation of pharmacological therapies and, possibly, for early diagnosis.