Journal of magnetic resonance imaging : JMRI
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J Magn Reson Imaging · Dec 2005
Quantifying CBF with pulsed ASL: technical and pulse sequence factors.
We summarize here current methods for the quantification of CBF using pulsed arterial spin labeling (ASL) methods. Several technical issues related to CBF quantitation are described briefly, including transit delay, signal from larger arteries, radio frequency (RF) slice profiles, magnetization transfer, tagging efficiency, and tagging geometry. ⋯ Velocity-selective ASL (VS-ASL) uses a new type of pulse labeling in which inflowing arterial spins are tagged based on their velocity rather than their spatial location. In principle, this technique may allow ASL measurement of cerebral blood flow (CBF) that is insensitive to transit delays.
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The basic principles of measuring cerebral blood flow (CBF) using arterial spin labeling (ASL) are reviewed. The measurement is modeled by treating the ASL method as a magnetic resonance imaging (MRI) version of a microsphere study, rather than a diffusible tracer study. This approach, particularly when applied to pulsed ASL (PASL) experiments, clarifies that absolute calibration of CBF primarily depends on global properties of blood, rather than local tissue properties such as the water partition coefficient or relaxation time. ⋯ The key to quantitative CBF measurements that compensate for this systematic error is to create a well-defined bolus of tagged blood and to ensure that all of the bolus has been delivered to an imaging voxel at the time of measurement. Two practical technical factors considered here are 1) producing a tagged bolus with a well-defined temporal width and 2) accounting for reduction in magnitude of the tagged magnetization due to relaxation. The ASL approach has the potential to provide a robust estimation of CBF, although the timing of water exchange into tissue and the effects of pulsatile flow require further investigation.
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J Magn Reson Imaging · Dec 2005
Arterial spin labeling in small animals: methods and applications to experimental cerebral ischemia.
ASL enables noninvasive, quantitative monitoring of cerebral perfusion to be performed repeatedly over a period of hours. Thus, ASL is an attractive method for basic science studies of the time evolution and pathophysiology of diseases using animal models. ⋯ Some technical factors pertinent to these studies are discussed, including a method for measuring arterial blood T(1) and double-echo PASL for measuring cerebral blood flow (CBF) and volume (CBV). Investigations of the CBF response to forebrain ischemia and reperfusion, and of regional variations in CBF and arterial transit time (ATT) are also discussed.
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J Magn Reson Imaging · Nov 2005
Multicenter Study Controlled Clinical TrialTexture analysis for tissue discrimination on T1-weighted MR images of the knee joint in a multicenter study: Transferability of texture features and comparison of feature selection methods and classifiers.
To investigate the reproducibility and transferability of texture features between MR centers, and to compare two feature selection methods and two classifiers. ⋯ The differences in texture features extracted from MR images from different centers seem to have only a small impact on the results of tissue discrimination.
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J Magn Reson Imaging · Nov 2005
Clinical TrialQuantifying the effect of posture on intracranial physiology in humans by MRI flow studies.
To quantify the effect of posture on intracranial physiology in humans by MRI, and demonstrate the relationship between intracranial compliance (ICC) and pressure (ICP), and the pulsatility of blood and CSF flows. ⋯ The effect of posture on intracranial physiology can be quantified by MRI because posture-related changes in ICC and ICP strongly affect the dynamics of cerebral blood and CSF flows. This study provides important insight into the coupling that exists between arterial, venous, and CSF flow dynamics, and how it is affected by posture.