Browsing by Subject "Cerebrovascular Circulation"
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Item Cerebral circulation in hypertension(1984-08-23) Reed, William GaryItem Effects of Aerobic Exercise Training on Carotid Arterial Stiffness and Brain Health in Traumatic Brain Injury(2020-05-01T05:00:00.000Z) Le, Tran B.; Ding, Kan; Zhang, Rong; Bell, Kathleen R.; Tomoto, TsubasaBACKGROUND: Vascular dysfunction and hypoperfusion in the brain are common after traumatic brain injury (TBI). The brain is perfused by elastic central arteries that decrease in compliance with age, leading to decreased ability to dampen hemodynamic pulsatility and decreased continuous blood flow in cerebral vasculature. Aerobic exercise improves cardiorespiratory fitness, health status, quality of life, and cognitive function as well as decrease mortality in normal adults. In this regard, physical activity, particularly aerobic exercise training (AET), may have favorable effects on TBI-related vascular and cerebral blood flow (CBF) changes. However, knowledge gaps regarding the effects of chronic TBI on vascular function still exist. Furthermore, little is known about the effect of AET on carotid arterial stiffness and CBF in patients with TBI with pre-existing brain injury. OBJECTIVE: We hypothesized that TBI patients may continue to suffer from vascular impairments at the chronic stage and may benefit from aerobic exercise with improvements in cardiorespiratory fitness, decrease in carotid arterial stiffness, and improved brain health. METHODS: Twenty-three participants with a history of mild to severe TBI and twenty-five age- gender-fitness level-matched participants with no history of TBI were recruited for the normal control group (non-TBI). All participants were 18-65 years old and have a sedentary lifestyle. The groups were divided into young (19-44 years old) and middle-aged (45-63 years old) for further analysis. Carotid arterial compliance was measured using common carotid artery echography and applanation tonometry. Transcranial Doppler was used to measure the cerebral blood flow velocities. Carotid arterial compliance was calculated from the carotid diameters and blood pressures. Seventeen of the TBI survivors (age: 48±13 years, 10 women) with persistent neurological symptoms 6-60 months after initial injury were randomized to 3-month moderate-intensity AET or control stretching program (SAT) and completed the interventions. Among them, 10 sustained mild TBI and 7 had moderate to severe TBI. Cardiorespiratory fitness was assessed by peak oxygen uptake (VO2peak) using a modified Astrand-Saltin treadmill protocol. Carotid arterial compliance was measured as measured. Neuropsychological function was assessed using the NIH Toolbox cognition battery and the PROMIS assessment. RESULTS: In the cross-sectional portion of the study, hemodynamic parameters indicate that the TBI group had higher brachial blood pressure (116.4 ± 10.4 vs. 109.8 ± 9.3 mmHg, p < 0.05). and carotid systolic blood pressure (113.0 ± 11.0 vs. 102.8 ± 10.6 mmHg, p < 0.05) than the non-TBI groups at rest. Arterial compliance was significantly lower in the TBI vs. non-TBI group (0.101 + 0.025 vs. 0.120 + 0.029 mm2/mmHg, p < 0.05). Additionally, cerebrovascular resistance was significantly higher in the TBI vs. non-TBI group (0.168 + 0.0332 vs. 0.145 + 0.0290 mmHg/mL/min, p < 0.05). Ten participants were randomized to AET group and seven to stretching group. No age, gender, or VO2peak differences were noted at baseline between AET and stretching groups. The duration of the intervention was twelve weeks. Although no statistically significant changes were observed following the intervention, different trends were observed. VO2peak increased by 7% in AET yet decreased by 4% in stretching; arterial compliance increased by 12 % in AET and decreased by 2% in stretching; NIH Toolbox fluid composite score, which assessed adaptability to new experience, improved by 15% in AET and 9% in stretching; and the NIH Toolbox total composite score, which involves adaptability to new experiences as well as past knowledge and skills, improved by 7% in AET versus 4% in stretching. CONCLUSION: The results suggest that TBI is associated with increased blood pressure, which is consistent with existing literature. The elevated blood pressure potentially leads is associated with decreased arterial compliance and increased resistance in the cerebral vasculature. Previous literature suggests that decreased cerebral blood flow may be associated with the cognitive impairment in TBI patients. For the longitudinal portion of the study, the physiological measurements (includingVO2peak, arterial compliance, and pulsatility index) and cognitive measurements suggest the potential positive effect of AET on physiological and cognitive improvement in patients with TBI. Physical activity, both SAT and AET, can improve arterial compliance in patients with chronic TBI.Item Measurement of Cerebral Blood Flow Using Arterial Spin Labeling Magnetic Resonance Imaging(2011-02-01) Aslan, Sina; Lu, HanzhangCerebral Blood Flow (CBF) reflects the amount of blood perfusion in the brain, often defined as ml of blood per 100 gram of brain per minute. CBF is an important measure in understanding brain physiology and pathophysiology. Thus, it is important to establish a robust method suitable for longitudinal and cross-sectional studies of neurovascular and neurodegenerative diseases non-invasively. Pseudo-Continuous Arterial Spin Labeling (pCASL) MRI is a new MRI technique that is able to detect blood flow changes, non-invasively. The blood flow change detected by pCASL MRI is relative and it is expressed in terms of arbitrary MRI units which does not have any physiological meaning. Thus, quantifying absolute CBF map is of a great interest. In the first part of this study, I quantified absolute CBF (aCBF) map by utilizing phase contrast MRI as a normalization factor. Next, I provided a systematic investigation into the detection power of ASL and the optimal strategies for data analysis. The power of ASL MRI in detecting CBF differences between patient and control subjects is hampered by inter-subject variations in global CBF, which are associated with non-neural factors and may contribute to the noise in the across-group comparison. I found that when normalizing the CBF with whole-brain CBF or CBF in a reference region (termed relative CBF, rCBF), the statistical significance was improved considerably (p<0.003). In the last part of this study, the aCBF of ten major brain human fibers were estimated for the first time and the relationship between Fractional Anisotropy (FA) and aCBF was investigated. The inverse association between aCBF and FA suggests that higher myelination restricted the blood flow to the center of the fiber or higher myelination made the conductance of the action potential more efficient. In summary, ASL MRI has become the method of choice for measuring cerebral blood flow and it has a great potential in clinical settings for diagnosis of most neurological disorders before anatomical changes are observed.Item Measurement of Cerebral Metabolism and Vascular Function with Magnetic Resonance Imaging(2012-08-13) Xu, Feng; Lu, HanzhangThe brain relies on oxidative metabolism to function properly. Cerebral metabolic rate of oxygen (CMRO2) is thus an important marker for brain health. Existing techniques for quantification of CMRO2 with positron emission tomography (PET) or magnetic resonance imaging (MRI) involve special equipment and/or exogenous agents, and may not be suitable for routine clinical studies. To fill this gap, I developed a noninvasive method for quantifying whole brain CMRO2. This method uses the Fick principle of arterio-venous difference for the calculation of CMRO2.and employs phase-contrast MRI for quantitative blood flow measurement and T2-relaxation-under-spin-tagging (TRUST) MRI for venous oxygenation estimation. During this thesis, I conducted several technical development studies. I first optimized TRUST and phase-contrast MR imaging parameters and demonstrated the ability to measure CMRO2 using completely non-invasive procedures. I further performed calibration and validations studies to show that blood oxygenation measured with TRUST reveals an excellent agreement with the gold standard Pulse Oximetry method. A final technical study was to improve the speed and reliability of TRUST MRI by shortening the scan duration by 60% while reducing the measuring error by half. I have also applied this novel CMRO2 method in better understanding brain physiology in younger and older adults. I studied the effect of CO2 inhalation (also known as hypercapnia) on brain metabolism. A reduced CMRO2 was observed and this effect was further supported by findings using functional connectivity MRI and electroencephalography techniques. I also investigated the effect of O2 modulation (hypoxia and hyperoxia) on brain metabolism and showed a dose dependent effect of O2 concentration on brain activity. Finally, I used this method to assess aged-related differences in brain metabolism and blood supply, and demonstrated a paradoxically higher metabolic rate in older adults, which may be associated with lower neural efficiency in elderly individuals.Item A Multi-Parametric Investigation of Vascular Alterations in Elderly with Hypertension(2015-01-26) Sheffield, Adam; Sheng, Min; King, Kevin; Ravi, Harshan; Peng, Shin-lei; Liu, Peiying; German, Zohre; Lu, HanzhangBACKGROUND: Along with aging comes many cardiovascular and cerebral changes that impact a person's health. These changes manifest as variances in blood pressure, brain volume, cerebral blood flow (CBF), oxygen metabolism, and neurological functioning. OBJECTIVE: The purpose of this study is to provide evidence to support new or previously known biomarkers for declining cerebrovascular health, such as cerebral arterial stiffness, reduced vessel capacity, and thickening of the extracellular matrix. METHODS: 45 participants ranging from the ages of 61 to 79 with a mean of 67 were studied using a 3 Tesla MRI. Several MRI techniques were employed to acquire and analyze data. Phase-contrast (PC) MRI was used for acquiring images of moving fluid, so that arteries containing blood flow to the brain could be isolated in order to calculate total CBF. Blood-oxygen-level dependent contrast images and end-tidal CO2 and O2 measurements were also obtained using MRI after the participants were given a different sequence of gases to breathe containing varying amounts of oxygen, carbon dioxide, and nitrogen. This allowed the cerebrovascular reactivity (CVR) and venous cerebral volume (vCBV) of the vessels to be determined. Venous oxygenation (Yv) was assessed using T2-relaxation-under-spin-tagging (TRUST) MRI technique. Linear regressions were performed to account for age, sex, and blood pressure. Data were also analyzed by putting participants with a systolic blood pressure greater than 140 into a hypertensive category for comparison. Other data acquired during or immediately prior to the MRI scans include systolic and diastolic blood pressure, brain volume, and the oxygen saturation level of venous and arterial blood. RESULTS: A p-value of <0.05 was used to determine significance. The CVR for the hypertensive group was lower than that of the non-hypertensive group (p<0.01) and CVR decreased as systolic blood pressure increased (p=0.02). CVR also decreased with increasing age (p=0.02) and was higher in males than in females (p<0.01). CBF increased with systolic blood pressure (p=0.03) and was higher in females (p=0.03). Yv also increased with systolic blood pressure (p=0.02) and correlated strongly with CBF values (p<0.001). CONCLUSION: These results support certain relationships between blood pressure and the vascular markers within the brain, which may appear before cognitive decline or clinical symptoms emerge. This study is an early step on the path to discovering easily identifiable precursors to neurological changes that take place as normal aging processes occur.Item Multiparametric Estimation of Brain Hemodynamics with MR Fingerprinting ASL(2018-12-28) Su, Pan; McColl, Roderick W.; Liu, Hanli; Pinho, Marco Da Cunha; Choi, Changho; Lu, HanzhangCerebral perfusion is a process of delivering of blood to tissue capillary beds, supplying sufficient nutrients and oxygen to the brain. It is an important physiology indicator of brain function. The disorder of perfusion such as cerebral vascular disease leads to physiological changes and impaired function of brain. Noninvasive imaging of brain perfusion would contribute significantly to the research of cerebral physiology and clinical application in cerebrovascular diseases. Arterial Spin Labeling (ASL) MRI technique is capable of estimating cerebral blood flow (CBF) without radioactive tracer or contrast agent. However, the signal from ASL is affected by multiple parameters in the kinetic model, causing the complexity in interpreting the underlying physiological mechanism. This thesis develops a novel non-contrast technique for assessing multiple hemodynamic parameters in a single MR scan less than four minutes. The concept of magnetic resonance fingerprinting (MRF) was incorporated into the framework of ASL technique, and a novel sequence, MRF-ASL, was proposed. It is a promising alternative technique in cerebrovascular patients who cannot receive contrast agent based MRI perfusion. This thesis consists of three major components. First, I developed an MR perfusion technique (MRF-ASL) that can provide non-contrast and multi-parametric estimation of hemodynamic markers, in particular measuring timing parameters that are critical for applications in cerebrovascular disease, e.g. bolus arrival time (BAT). Feasibility, reproducibility, comparison to conventional multi-delay ASL and sensitivity were studied. Second, I optimized the key component in MRF-ASL, the TR timing sequence and further increased the spatial coverage of MRF-ASL with multi-slice acquisition. Then with the optimized sequence, I validated the MRF-ASL derived hemodynamic maps with Dynamic Susceptibility Contrast (DSC) MRI. The results showed that these two methods provided visually consistent and quantitatively correlated estimations of CBF and BAT results. Finally, I demonstrated the clinical utility of MRF-ASL by applying our technique to two types of cerebrovascular diseases, ischemic stroke and Moyamoya disease. Results showed that MRF-ASL can detect the prolonged bolus arrival and decreased CBF in these two diseases.Item [News](1984-08-31) Harrell, AnnItem Optimization of the Fair Technique for Specific Brain Region Perfusion Studies(2009-01-14) Li, Xiufeng; Briggs, Richard W.Most of the technical development and applications of ASL (arterial spin labeling) imaging have mainly focused on the superior cortical regions of the brain. However, optimal ASL measurements to quantify cerebral blood flow (CBF) in specific brain regions may require optimized parameters, improved techniques, or new imaging schemes based upon physiological or anatomic characteristics of those brain regions. In this thesis, the advantages of this region-targeted approach are demonstrated by performing quantitative perfusion studies of two representative brain regions, the cerebellum in the inferior part of the brain and the hippocampus in the mid-brain. To minimize or eliminate the venous artifacts found in cerebellum perfusion studies using traditional FAIR (flow-sensitive alternating inversion recovery) technique, FAIR ASST (FAIR with active suppression of superior tagging technique), as well as MDS FAIR, (modulated dual saturation pulse trains for FAIR) was developed and compared to PICORE (proximal inversion with a control for off-resonance effects) for quantifying cerebellum perfusion. The data indicate that FAIR ASST yields more robust CBF (cerebral blood flow) measurements. OPTIMAL FAIR (orthogonally-positioned tagging imaging method for arterial labeling of FAIR) was developed and shown to reduce the heterogeneity of within-slice transit time and to minimize partial volume effects, improving quantitative CBF maps for cerebellum and hippocampus. These techniques were optimized and applied to the study of perfusion abnormalities in brain regions important to the study of Gulf War Syndrome. Together with regionally optimized parameters, these ASL methods provide more reliable, efficient, accurate, and artifact-free CBF measurements than methods previously available.