Author: Ciwen Wang
Publisher:
ISBN:
Category :
Languages : en
Pages : 74

Get Book Here

Book Description
Arterial Spin Labeling (ASL) is one family of perfusion-weighted contrast imaging techniques of Magnetic Resonance Imaging (MRI) that measures cerebral blood flow by labeling spins in arterial blood with inversion and then waiting for a certain period of time for the labeled arterial blood to enter the imaging plane, and then acquiring MR image at the image plane. In compare with PET, ASL is a noninvasive new technology. But as a new technology, it is not very commonly used because of the relatively low signal to noise ratio, less robust mechanism, and more important, there is no standard for clinical applications. One goal of this study is to find out the optimal imaging processing way and parameters for ASL processing. The other goal is to find the relationship between CBF and age. There are 173 subjects, with 107 female subjects and 66 male subjects. Pseudo-continuous ASL (PCASL) was used as labeling sequence and multi-slice single shot 2D Echo-planar imaging (EPI) was used as MR image acquisition sequence. 40 pairs of control-labeled images were taken in order to increase signal to noise ratio. An MPRAGE T1 image was taken for each subject as brain structure reference. Label duration = 1650ms; post label delay = 1525ms; TR = 4260ms or 4210.8ms; TE=14ms. EPI factor = 35ms. Voxel size = 3x3x5 mm; FOV = 240x240x145 mm; slice number = 29. FSL which is a MRI image processing tool developed by Oxford was used in imaging processing. dcm2nii was used for DICOM to NIFTY conversion. MCFLIRT was used for motion correction. Trilinear interpolation was used in MCFLIRT. In spatial smoothing, a 3D Gaussian kernel with FWHM = 6mm was used. In M0 magnetization baseline calculation, the average magnetization of the whole brain of mean control image was used, so that the T1 recovery time was assumed to be the time from labeling to image acquisition of the middle slice (15th slice). The longitudinal relaxation time of blood was used as T1 value of the tissue. In Cerebral Blood Flow (CBF) calculation, also the longitudinal relaxation time of blood was used as T1 value of the tissue. A threshold of 0-300 was used on the CBF map. Voxels below 0 was assigned 0, and above 300 was assigned 300. CBF map was first co-registered on the T1 structural image of the same subject, and then, with the help of the high resolution T1, CBF map was normalized on MNI152 template. Relative CBF map was calculated by dividing the value of each voxel by the mean value of the whole brain CBF. The voxelwise analysis results (p

Author: Jingyi Xie
Publisher:
ISBN:
Category : Brain
Languages : en
Pages : 134

Get Book Here

Book Description

Author: Lorna A. Smith
Publisher:
ISBN:
Category :
Languages : en
Pages : 690

Get Book Here

Book Description
Differences in cerebral blood flow (CBF) have been identified between older individuals in good cognitive health and those experiencing cognitive decline and dementia. Previous studies have shown that the aetiology of dementia includes a substantial vascular component and there is evidence that CBF decline in old age may be linked to cardiovascular disease. Although the incidence, prevalence and impact of vascular risk varies by ethnicity and gender, many previous studies have focused on participants of white European origin or have pooled ethnically diverse samples, while differences between sexes have been under-investigated. This thesis used arterial spin labelling (ASL) to measure cortical CBF in an elderly tri-ethnic population cohort and examined its relationship with vascular risk and the brain ageing markers of cortical volume and white matter hyperintensity (WMH) volume from magnetic resonance imaging (MRI). Chapter 4 showed that use of the currently recommended mean haematocrit (Hct) value in equations that calculate CBF from ASL underestimated CBF in women and non-European ethnicities. The alternative method of substituting individually measured Hct into the equation was implemented in the following chapters. Results from Chapter 5 indicated that increased vascular risk factors were associated with lower CBF, but these relationships varied by ethnicity and sex. Ethnicity and sex also modified the strength of associations of increased vascular risk with decreased cortical tissue volume and increased volume of WMHs examined in Chapter 6. However, there was no evidence of any association of CBF with the MRI markers of brain ageing.

Author: Mohammad Ahmad Awad
Publisher:
ISBN:
Category : Anatomy
Languages : en
Pages : 56

Get Book Here

Book Description
Arterial spin labeling (ASL) is a magnetic resonance imaging (MRI) technique used for measuring cerebral blood flow (CBF) in a completely non-ionizing and noninvasive fashion. ASL is useful in perfusion studies on healthy adult & pediatric subjects, individuals who need multiple follow-ups, and patients with varying cerebrovascular diseases where changes in CBF can be used as an indicator of tissue viability. We used a variation of the ASL technique known as pseudo-continuous ASL (pCASL). This form of ASL is the clinical standard (Alsop et al., 2015). However, it is not well documented the that pCASL is reliable between sessions spanning days to weeks. In this study, we assessed the inter-session reliability of CBF through the use of the pCASL technique. We hypothesize that the pCASL technique can be used to quantify CBF measurements across a 24-hour and 48-hour period. Subjects included 15 healthy, active duty Air Force military personnel recruited by the Wright Patterson Air Force Base from a larger experiment. Of the 15 subjects scanned on day 1 and day 2, 2 did not return for scanning on the third day. All participants were scanned in three identical evening sessions separated by 24 hours. MR imaging was conducted on a 3T MRI scanner with a 24-channel head coil. Each of the three days began with a baseline imaging scan followed by sham transcranial direct current stimulation (tDCS) and another identical imaging session. MRI acquisition included a 12-min resting-state function MRI (fMRI), three task fMRI, a T1-weighted MRI, diffusion tensor imaging (DTI), magnetic resonance spectroscopy (MRS) imaging, and resting pCASL. Our work only shows the baseline imaging from each day and the resting pCASL results. Quantitative CBF maps were computed from the raw pCASL data using proton density maps and a single compartment perfusion model through the use of the clinical processing pipeline on the MRI. These CBF maps were then registered to a reference space. Changes in CBF between the three pre-sham stimulation days were analyzed on a voxel-wise basis through a one-sample t-test and permutation testing using 215 (32,768) permutations for the difference between day 1 and day 2 and 213 (8192) permutations for the difference between day 1 and day 3 and day 2 and day 3. Permutation test results were not cluster-corrected for multiple comparisons to be conservative with respect to our hypothesis but were thresholded with a t-statistic of 2.3. The experiment's results indicated that the pCASL MRI technique can indeed be used reliably in radiological evaluation to quantitatively assess CBF within a 24-hour but not quite in a 48-hour periods.

Author: Teemu Myllylä
Publisher:
ISBN:
Category : Medical
Languages : en
Pages : 0

Get Book Here

Book Description
In this chapter, we review state-of-the-art non-invasive techniques to monitor and study cerebral circulation in humans. The measurement methods can be divided into two categories: direct and indirect methods. Direct methods are mostly based on using contrast agents delivered to blood circulation. Clinically used direct methods include single-photon emission computed tomography (SPECT), positron emission tomography (PET), magnetic resonance imaging (MRI) with contrast agents, xenon computed tomography (CT), and arterial spin labeling (ASL) MRI. Indirect techniques are based on measuring physiological parameters reflecting cerebral perfusion. The most commonly used indirect methods are near-infrared spectroscopy (NIRS), transcranial Doppler ultrasound (TCD), and phase-contrast MRI. In recent years, few more techniques have been intensively developed, such as diffuse correlation spectroscopy (DCS) and microwave-based techniques, which are still emerging as methods for cerebral circulation monitoring. In addition, methods combining different modalities are discussed and, as a summary, the presented techniques and their benefits for cerebral circulation will be compared.

Author: Michael Chappell
Publisher: Oxford University Press
ISBN: 0198793812
Category : Medical
Languages : en
Pages : 157

Get Book Here

Book Description
ASL is an increasingly popular tool to study the brain. The aim of this primer is to equip someone new to the field with the knowledge to make informed choices about ASL acquisition and analysis. While providing a stand-alone introduction to this subject, the text can be read with others in the series for a comprehensive overview of neuroimaging.

Author: Lydiane Hirschler
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

Get Book Here

Book Description
Cerebral blood flow (CBF) characterizes the blood supply to brain tissue. This perfusion-related parameter contributes in diagnosis and therapeutic follow-up in many diseases. The least invasive technique to measure CBF is arterial spin labeling (ASL), where arterial water is used as tracer. The aim of this PhD project, conducted within a CIFRE agreement (Convention Industrielle de Formation par la REcherche), was to increase the performance and to facilitate the use of continuous and pseudo-continuous arterial spin labeling (CASL, pCASL) tools in preclinical studies. CBF quantification by means of ASL is one of the most challenging MRI modalities in terms of the workflow, since additional adjustments, acquisitions and post-processing steps are required. First, to render the workflow smoother for the user, a CASL package has been developed in collaboration with Bruker. This workflow allows easier relative and absolute CBF measurements, thanks to the integration of automated adjustments and reconstruction steps. In a second step, problems arising at high magnetic field were addressed. A strategy to optimize the pCASL labeling sequence in order to obtain robust results was developed and its robustness towards suboptimal shim conditions was demonstrated at 9.4 T in rats. The developed pCASL-package, consisting of three sequences, was shared with ten other institutes worldwide. Another issue encountered at high magnetic fields is heating due to RF power deposition, which was assessed locally in the brain and in the carotids, as well as globally, for the CASL and pCASL sequences and for two different transmit coil configurations. In a third step, time-encoded pCASL was developed in mice in collaboration with teams of the Leiden University Medical Center. This tool enables the simultaneous mapping of CBF and arterial transit time, a parameter that can reflect underlying pathologies such as increased vessel tortuosity or occlusion.

Author: Marilyn J. Cipolla
Publisher: Biota Publishing
ISBN: 1615047239
Category : Medical
Languages : en
Pages : 82

Get Book Here

Book Description
This e-book will review special features of the cerebral circulation and how they contribute to the physiology of the brain. It describes structural and functional properties of the cerebral circulation that are unique to the brain, an organ with high metabolic demands and the need for tight water and ion homeostasis. Autoregulation is pronounced in the brain, with myogenic, metabolic and neurogenic mechanisms contributing to maintain relatively constant blood flow during both increases and decreases in pressure. In addition, unlike peripheral organs where the majority of vascular resistance resides in small arteries and arterioles, large extracranial and intracranial arteries contribute significantly to vascular resistance in the brain. The prominent role of large arteries in cerebrovascular resistance helps maintain blood flow and protect downstream vessels during changes in perfusion pressure. The cerebral endothelium is also unique in that its barrier properties are in some way more like epithelium than endothelium in the periphery. The cerebral endothelium, known as the blood-brain barrier, has specialized tight junctions that do not allow ions to pass freely and has very low hydraulic conductivity and transcellular transport. This special configuration modifies Starling's forces in the brain microcirculation such that ions retained in the vascular lumen oppose water movement due to hydrostatic pressure. Tight water regulation is necessary in the brain because it has limited capacity for expansion within the skull. Increased intracranial pressure due to vasogenic edema can cause severe neurologic complications and death.

Author: Rajiv G. Menon
Publisher:
ISBN:
Category : Blood water
Languages : en
Pages : 33

Get Book Here

Book Description

Author: Jean Chen
Publisher: Humana
ISBN: 9781071617625
Category : Medical
Languages : en
Pages : 218

Get Book Here

Book Description
This volume provides a comprehensive overview of the methodology, physiology, and contemporary and novel applications of cerebrovascular reactivity (CVR) measurements. The chapters in this book cover topics such as an introduction of the neurophysiology, neuroimaging, and clinical methods for CVR measurement; the use of CVR methods in the study of aging, cerebrovascular dysfunction, dementia, and brain tumors; and recommendations for measurement protocols and future applications in clinical translation. In Neuromethods series style, chapters include the kind of detail and key advice from the specialists needed to get successful results in your research center and clinical investigation. Thorough and comprehensive, Cerebrovascular Reactivity: Methodological Advances and Clinical Applications is a valuable tool that provides researchers in neuroscience and neurology with the latest resources on the measurement, interpretation, and application of CVR measurement.