The Experts below are selected from a list of 11559 Experts worldwide ranked by ideXlab platform
David C Alsop - One of the best experts on this subject based on the ideXlab platform.
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volumetric measurement of perfusion and Arterial transit delay using hadamard encoded continuous Arterial Spin Labeling
Magnetic Resonance in Medicine, 2013Co-Authors: Ajit Shankaranarayanan, David C AlsopAbstract:Creating images of the transit delay from the Labeling location to image tissue can aid the optimization and quantification of Arterial Spin Labeling perfusion measurements and may provide diagnostic information independent of perfusion. Unfortunately, measuring transit delay requires acquiring a series of images with different Labeling timing that adds to the time cost and increases the noise of the Arterial Spin Labeling study. Here, we implement and evaluate a proposed Hadamard encoding of Labeling that speeds the imaging and improves the signal-to-noise ratio efficiency. Volumetric images in human volunteers confirmed the theoretical advantages of Hadamard encoding over sequential acquisition of images with multiple Labeling timing. Perfusion images calculated from Hadamard encoded acquisition had reduced signal-to-noise ratio relative to a dedicated perfusion acquisition with either assumed or separately measured transit delays, however. Magn Reson Med 69:1014–1022, 2013. © 2012 Wiley Periodicals, Inc.
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Arterial Spin Labeling mr imaging of renal masses correlation with histopathologic findings
Radiology, 2012Co-Authors: R S Lanzman, David C Alsop, Philip M Robson, Amish D Patel, Kimiknu Mentore, Andrew A Wagner, Elizabeth M Genega, Neil M Rofsky, Ivan PedrosaAbstract:Arterial Spin-Labeling MR imaging might contribute substantially to the noninvasive assessment of renal tumors and offer complementary results to percutaneous biopsy, particularly in those patients with inconclusive results.
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optimization of background suppression for Arterial Spin Labeling perfusion imaging
Magnetic Resonance Materials in Physics Biology and Medicine, 2012Co-Authors: Nasim Maleki, David C AlsopAbstract:Object To present an algorithm for optimization of background suppression pulse timing for Arterial Spin Labeling (ASL) perfusion imaging.
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time resolved vessel selective digital subtraction mr angiography of the cerebral vasculature with Arterial Spin Labeling
Radiology, 2010Co-Authors: Philip M Robson, Neil M Rofsky, Ajit Shankaranarayanan, David C AlsopAbstract:MR imaging and Arterial Spin Labeling can be used to perform cerebral angiography with dynamic inflow and vessel-specific information that is similar to that obtained with conventional x-ray digital subtraction angiography.
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amplitude modulated continuous Arterial Spin Labeling 3 0 t perfusion mr imaging with a single coil feasibility study
Radiology, 2005Co-Authors: Jiongjiong Wang, Yan Zhang, David C Alsop, Ronald L Wolf, John A. DetreAbstract:Written informed consent was obtained prior to all human studies after the institutional review board approved the protocol. A continuous Arterial Spin-Labeling technique with an amplitude-modulated control was implemented by using a single coil at 3.0 T. Adiabatic inversion efficiency at 3.0 T, comparable to that at 1.5 T, was achieved by reducing the amplitude of radiofrequency pulses and gradient strengths appropriately. The amplitude-modulated control provided a good match for the magnetization transfer effect of Labeling pulses, allowing multisection perfusion magnetic resonance imaging of the whole brain. Comparison of multisection continuous and pulsed Arterial Spin-Labeling methods at 3.0 T showed a 33% improvement in signal-to-noise ratio by using the former approach.
John A. Detre - One of the best experts on this subject based on the ideXlab platform.
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Temporal and Spatial Variances in Arterial Spin-Labeling Are Inversely Related to Large-Artery Blood Velocity.
American Journal of Neuroradiology, 2017Co-Authors: Andrew D. Robertson, G. Matta, V.s. Basile, Sandra E. Black, Christopher K. Macgowan, John A. Detre, Bradley J. MacintoshAbstract:BACKGROUND AND PURPOSE: The relationship between extracranial large-artery characteristics and Arterial Spin-Labeling MR imaging may influence the quality of Arterial Spin-Labeling–CBF images for older adults with and without vascular pathology. We hypothesized that extracranial Arterial blood velocity can explain between-person differences in Arterial Spin-Labeling data systematically across clinical populations. MATERIALS AND METHODS: We performed consecutive pseudocontinuous Arterial Spin-Labeling and phase-contrast MR imaging on 82 individuals (20–88 years of age, 50% women), including healthy young adults, healthy older adults, and older adults with cerebral small vessel disease or chronic stroke infarcts. We examined associations between extracranial phase-contrast hemodynamics and intracranial Arterial Spin-Labeling characteristics, which were defined by Labeling efficiency, temporal signal-to-noise ratio, and spatial coefficient of variation. RESULTS: Large-artery blood velocity was inversely associated with Labeling efficiency ( P = .007), temporal SNR ( P P = .05) of Arterial Spin-Labeling, after accounting for age, sex, and group. Correction for Labeling efficiency on an individual basis led to additional group differences in GM-CBF compared to correction using a constant Labeling efficiency. CONCLUSIONS: Between-subject Arterial Spin-Labeling variance was partially explained by extracranial velocity but not cross-sectional area. Choosing Arterial Spin-Labeling timing parameters with on-line knowledge of blood velocity may improve CBF quantification.
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Arterial Spin Labeling mri clinical applications in the brain
Journal of Magnetic Resonance Imaging, 2015Co-Authors: Nicholas A Telischak, John A. Detre, Greg ZaharchukAbstract:: Visualization of cerebral blood flow (CBF) has become an important part of neuroimaging for a wide range of diseases. Arterial Spin Labeling (ASL) perfusion magnetic resonance imaging (MRI) sequences are increasingly being used to provide MR-based CBF quantification without the need for contrast administration, and can be obtained in conjunction with a structural MRI study. ASL MRI is useful for evaluating cerebrovascular disease including arterio-occlusive disease, vascular shunts, for assessing primary and secondary malignancy, and as a biomarker for neuronal metabolism in other disorders such as seizures and neurodegeneration. In this review we briefly outline the various ASL techniques including advantages and disadvantages of each, methodology for clinical interpretation, and clinical applications with specific examples.
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Comparison of Arterial transit times estimated using Arterial Spin Labeling
Magnetic Resonance Materials in Physics Biology and Medicine, 2011Co-Authors: Yufen Chen, Danny J.j. Wang, John A. DetreAbstract:Objective To compare Arterial transit time estimates from two efficient transit time mapping techniques using Arterial Spin Labeling (ASL)—flow encoded Arterial Spin tagging (FEAST) and Look-Locker ASL (LL-ASL). The effects of bipolar gradients and label location were investigated.
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Arterial Spin Labeling perfusion mri in pediatric Arterial ischemic stroke initial experiences
Journal of Magnetic Resonance Imaging, 2009Co-Authors: Juan Chen, John A. Detre, Daniel J Licht, Sabrina E Smith, Shannon C Agner, Stefanie E Mason, Sumei Wang, David W Silvestre, Robert A Zimmerman, Rebecca IchordAbstract:Purpose To investigate the feasibility and utility of Arterial Spin Labeling (ASL) perfusion MRI in characterizing alterations of cerebral blood flow (CBF) in pediatric patients with Arterial ischemic stroke (AIS).
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Physiological Modulations in Arterial Spin Labeling Perfusion Magnetic Resonance Imaging
IEEE Transactions on Medical Imaging, 2009Co-Authors: Wenchau Wu, Brian L Edlow, Jiongjiong Wang, Mark A. Elliot, John A. DetreAbstract:The purpose of this study is to evaluate cardiac and respiratory modulations in the signals of Arterial Spin Labeling (ASL) perfusion magnetic resonance imaging (MRI) using RETROICOR, an image domain based retrospective correction method. Systematic comparisons were conducted for tagging schemes, pulsed (PASL) versus frequency-modulated continuous (CASL) methods, and the use of background suppression (BGS). Results showed that cardiac pulsation accounted for more signal fluctuation in PASL than in CASL (two-tailed paired student's t-test, p
Peter Jezzard - One of the best experts on this subject based on the ideXlab platform.
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Vessel-encoded dynamic magnetic resonance angiography using Arterial Spin Labeling.
Magnetic resonance in medicine, 2010Co-Authors: Thomas W Okell, Matthias Günther, Michael A Chappell, Mark W Woolrich, David A Feinberg, Peter JezzardAbstract:A new noninvasive MRI method for vessel selective angiography is presented. The technique combines vessel-encoded pseudocontinuous Arterial Spin Labeling with a two-dimensional dynamic angiographic readout and was used to image the cerebral arteries in healthy volunteers. Time-of-flight angiograms were also acquired prior to vessel-selective dynamic angiography acquisitions in axial, coronal, and/or sagittal planes, using a 3-T MRI scanner. The latter consisted of a vessel-encoded pseudocontinuous Arterial Spin Labeling pulse train of 300 or 1000 ms followed by a two-dimensional thick-slab flow-compensated fast low angle shot readout combined with a segmented Look-Locker sampling strategy (temporal resolution = 55 ms). Selective Labeling was performed at the level of the neck to generate individual angiograms for both right and left internal carotid and vertebral arteries. Individual vessel angiograms were reconstructed using a bayesian inference method. The vessel-selective dynamic angiograms obtained were consistent with the time-of-flight images, and the longer of the two vessel-encoded pseudocontinuous Arterial Spin Labeling pulse train durations tested (1000 ms) was found to give better distal vessel visibility. This technique provides highly selective angiograms quickly and noninvasively that could potentially be used in place of intra-Arterial x-ray angiography for larger vessels.
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Vessel‐encoded dynamic magnetic resonance angiography using Arterial Spin Labeling
Magnetic Resonance in Medicine, 2010Co-Authors: Thomas W Okell, Matthias Günther, Michael A Chappell, Mark W Woolrich, David A Feinberg, Peter JezzardAbstract:A new noninvasive MRI method for vessel selective angiography is presented. The technique combines vessel-encoded pseudocontinuous Arterial Spin Labeling with a two-dimensional dynamic angiographic readout and was used to image the cerebral arteries in healthy volunteers. Time-of-flight angiograms were also acquired prior to vessel-selective dynamic angiography acquisitions in axial, coronal, and/or sagittal planes, using a 3-T MRI scanner. The latter consisted of a vessel-encoded pseudocontinuous Arterial Spin Labeling pulse train of 300 or 1000 ms followed by a two-dimensional thick-slab flow-compensated fast low angle shot readout combined with a segmented Look-Locker sampling strategy (temporal resolution = 55 ms). Selective Labeling was performed at the level of the neck to generate individual angiograms for both right and left internal carotid and vertebral arteries. Individual vessel angiograms were reconstructed using a bayesian inference method. The vessel-selective dynamic angiograms obtained were consistent with the time-of-flight images, and the longer of the two vessel-encoded pseudocontinuous Arterial Spin Labeling pulse train durations tested (1000 ms) was found to give better distal vessel visibility. This technique provides highly selective angiograms quickly and noninvasively that could potentially be used in place of intra-Arterial x-ray angiography for larger vessels. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc.
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assessment of Arterial arrival times derived from multiple inversion time pulsed Arterial Spin Labeling mri
Magnetic Resonance in Medicine, 2010Co-Authors: Bradley J. Macintosh, Michael A Chappell, Mark W Woolrich, Nicola Filippini, Clare E Mackay, Peter JezzardAbstract:The purpose of this study was to establish a normal range for the Arterial arrival time (AAT) in whole-brain pulsed Arterial Spin Labeling (PASL) cerebral perfusion MRI. Healthy volunteers (N = 36, range: 20 to 35 years) provided informed consent to participate in this study. AAT was assessed in multiple brain regions, using three-dimensional gradient and Spin echo (GRASE) pulsed Arterial Spin Labeling at 3.0 T, and found to be 641 ± 95, 804 ± 91, 802 ± 126, and 935 ± 108 ms in the temporal, parietal, frontal, and occipital lobes, respectively. Mean gray matter AAT was found to be 694 ± 89 ms for females (N = 15), which was significantly shorter than for men, 814 ± 192 ms (N = 21; P < 0.0003), and significant after correcting for brain volume (P < 0.001). Significant AAT sex differences were also found using voxelwise permutation testing. An atlas of AAT values across the healthy brain is presented here and may be useful for future experiments that aim to quantify cerebral blood flow from ASL data, as well as for clinical comparisons where disease pathology may lead to altered AAT. Pulsed Arterial Spin Labeling signals were simulated using an identical sampling scheme as the empiric study and revealed AAT can be estimated robustly when simulated arrival times are well beyond the normal range. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc.
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optimal design of pulsed Arterial Spin Labeling mri experiments
Magnetic Resonance in Medicine, 2008Co-Authors: Daniel Gallichan, Peter Jezzard, Roger N GunnAbstract:Quantitative measurement of cerebral blood flow (CBF) using Arterial Spin Labeling (ASL) MRI requires the acquisition of multiple inversion times (TIs) and the application of an appropriate kinetic model. The choice of these sampling times will have an impact on the precision of the estimated parameters. Here, optimal sampling schedule (OSS) design techniques, based on the Fisher Information approach, are applied in order to derive an optimal sampling scheme for pulsed Arterial Spin Labeling (PASL) experiments. Such an approach should improve the precision of parameter estimation from experimental data, and provide a formal framework for optimally selecting a limited number of samples. In this study, we aimed to optimize the estimation precision of CBF and bolus arrival time from the PASL data. The performance of OSS was compared to a more standard evenly distributed sampling schedule (EDS) using both simulated and measured experimental data sets. It was found that OSS was able to significantly improve the precision of parameter estimation in PASL studies that sought to estimate either both CBF and bolus arrival time, or CBF alone.
Eric C. Wong - One of the best experts on this subject based on the ideXlab platform.
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New developments in Arterial Spin Labeling pulse sequences.
NMR in Biomedicine, 2013Co-Authors: Eric C. WongAbstract:Since it was introduced over 20 years ago, Arterial Spin Labeling and related methods have steadily evolved over the years, and the field has seen not only improvements in technical specifications, such as signal-to-noise ratio and accuracy, but also the introduction of methods that allow for the collection of new information, such as maps of vascular territories and measurement of venous oxygenation. Some of these recent advances are reviewed here. Copyright © 2013 John Wiley & Sons, Ltd.
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multiphase pseudocontinuous Arterial Spin Labeling mp pcasl for robust quantification of cerebral blood flow
Magnetic Resonance in Medicine, 2010Co-Authors: Youngkyoo Jung, Eric C. WongAbstract:Pseudocontinuous Arterial Spin Labeling (PCASL) has been demonstrated to provide the sensitivity of the continuous Arterial Spin Labeling method while overcoming many of the limitations of that method. Because the specification of the phases in the radiofrequency pulse train in PCASL defines the tag and control conditions of the flowing Arterial blood, its tagging efficiency is sensitive to factors, such as off-resonance fields, that induce phase mismatches between the radiofrequency pulses and the flowing Spins. As a result, the quantitative estimation of cerebral blood flow with PCASL can exhibit a significant amount of error when these factors are not taken into account. In this paper, the sources of the tagging efficiency loss are characterized and a novel PCASL method that utilizes multiple phase offsets is proposed to reduce the tagging efficiency loss in PCASL. Simulations are performed to evaluate the feasibility and the performance of the proposed method. Quantitative estimates of cerebral blood flow obtained with multiple phase offset PCASL are compared to estimates obtained with conventional PCASL and pulsed Arterial Spin Labeling. Our results show that multiple phase offset PCASL provides robust cerebral blood flow quantification while retaining much of the sensitivity advantage of PCASL. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc.
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Quantitative Assessment of Mixed Cerebral Vascular Territory Supply With Vessel Encoded Arterial Spin Labeling MRI
Stroke, 2008Co-Authors: Akash P. Kansagra, Eric C. WongAbstract:Background and Purpose—Recent advances in Arterial Spin Labeling MRI have permitted noninvasive evaluation of vascular territories. In the present study, we quantitatively assess mixing of internal carotid and basilar artery blood through cerebrovascular anastomoses using vessel-encoded Arterial Spin Labeling and a new postprocessing method. Methods—Vessel-encoded Arterial Spin Labeling was used to determine the territories of the internal carotid and basilar arteries in 14 healthy subjects and one patient with asymptomatic high-grade carotid artery stenosis before and after endarterectomy. Contributions to individual vascular territories were quantified using a voxelwise supply fraction algorithm and the results were correlated with MR angiography. Results—Vascular territories were consistent with cerebrovascular anatomy and the presence of pathology. The supply fraction method allowed quantification of mixed territorial supply arising from collateral flow and showed vascular supply changes in a patient with carotid artery stenosis after endarterectomy. Conclusions—Vascular territories obtained with vessel-encoded Arterial Spin Labeling correlate with cerebrovascular anatomy and allow quantitative assessment of mixed territorial supply in subjects with and without pathology. (Stroke. 2008;39:2980-2985.)
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velocity selective Arterial Spin Labeling
Magnetic Resonance in Medicine, 2006Co-Authors: Eric C. Wong, Matthew V Cronin, Wenchau Wu, Ben Inglis, Lawrence R FrankAbstract:In pathologies in which slow or collateral flow conditions may exist, conventional Arterial Spin Labeling (ASL) methods that apply magnetic tags based on the location of Arterial Spins may not provide robust measures of cerebral blood flow (CBF), as the transit delay for the delivery of blood to target tissues may far exceed the relaxation time of the tag. Here we describe current methods for ASL with velocity-selective (VS) tags (termed VSASL) that do not require spatial selectivity and can thus provide quantitative measures of CBF under slow and collateral flow conditions. The implementation of a robust multislice VSASL technique is described in detail, and data obtained with this technique are compared with those obtained with conventional pulsed ASL (PASL). The technical considerations described here include the design of VS pulses, background suppression, anisotropy with respect to velocity-encoding directions, and CBF quantitation issues. Magn Reson Med, 2006. © 2006 Wiley-Liss, Inc.
David L. Thomas - One of the best experts on this subject based on the ideXlab platform.
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Arterial Spin Labeling perfusion of the brain emerging clinical applications
Radiology, 2016Co-Authors: Sven Haller, David L. Thomas, Greg Zaharchuk, Karlolof Lovblad, Frederik Barkhof, Xavier GolayAbstract:For many diseases, including dementia, vascular diseases, neoplasms, and various psychiatric diseases, Arterial Spin Labeling provides additional and complimentary information to that available from structural MR imaging.
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Cardiac Arterial Spin Labeling using segmented ECG-gated Look-Locker FAIR: Variability and repeatability in preclinical studies
Magnetic Resonance in Medicine, 2013Co-Authors: Adrienne E. Campbell-washburn, Anthony N. Price, Jack A. Wells, Roger J. Ordidge, David L. Thomas, Mark F LythgoeAbstract:MRI is important for the assessment of cardiac structure and function in preclinical studies of cardiac disease. Arterial Spin Labeling techniques can be used to measure perfusion noninvasively. In this study, an electrocardiogram-gated Look-Locker sequence with segmented k-space acquisition has been implemented to acquire single slice Arterial Spin Labeling data sets in 15 min in the mouse heart. A data logger was introduced to improve data quality by: (1) allowing automated rejection of respiration-corrupted images, (2) providing additional prospective gating to improve consistency of acquisition timing, and (3) allowing the recombination of uncorrupted k-space lines from consecutive data sets to reduce respiration corruption. Finally, variability and repeatability of perfusion estimation within-session, between-session, between-animal, and between image rejection criteria were assessed in mice. The criterion used to reject images from the T(1) fit was shown to affect the perfusion estimation. These data showed that the between-animal coefficient of variability (24%) was greater than the between-session variability (17%) and within-session variability (11%). Furthermore, the magnitude of change in perfusion required to detect differences was 30% (within-session) and 55% (between-session) according to Bland-Altman repeatability analysis. These technique developments and repeatability statistics will provide a platform for future preclinical studies applying cardiac Arterial Spin Labeling. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
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cardiac Arterial Spin Labeling using segmented ecg gated look locker fair variability and repeatability in preclinical studies
Magnetic Resonance in Medicine, 2013Co-Authors: Adrienne E Campbellwashburn, Anthony N. Price, Jack A. Wells, Roger J. Ordidge, David L. Thomas, Mark F LythgoeAbstract:MRI is important for the assessment of cardiac structure and function in preclinical studies of cardiac disease. Arterial Spin Labeling techniques can be used to measure perfusion noninvasively. In this study, an electrocardiogram- gated Look-Locker sequence with segmented k-space acquisition has been implemented to acquire single slice Arterial Spin Labeling data sets in 15 min in the mouse heart. A data logger was introduced to improve data quality by: (1) allowing automated rejection of respiration-corrupted images, (2) providing additional prospective gating to improve consistency of acquisition timing, and (3) allowing the recombination of uncorrupted k-space lines from consecutive data sets to reduce respiration corruption. Finally, variability and repeatability of perfusion estimation within-session, between-session, between-animal, and between image rejection criteria were assessed in mice. The criterion used to reject images from the T 1 fit was shown to affect the perfusion estimation. These data showed that the between-animal coefficient of variability (24%) was greater than the between-session variability (17%) and within-session variability (11%). Furthermore, the magnitude of change in perfusion required to detect differences was 30% (within-session) and 55% (between-session) according to Bland-Altman repeatability analysis. These technique developments and repeatability statistics will provide a platform for future preclinical studies applying cardiac Arterial Spin Labeling. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc. Copyright © 2012 Wiley Periodicals, Inc.
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In vivo hadamard encoded continuous Arterial Spin Labeling (H‐CASL)
Magnetic Resonance in Medicine, 2010Co-Authors: Jack A. Wells, Mark F Lythgoe, Roger J. Ordidge, David G. Gadian, David L. ThomasAbstract:Continuous Arterial Spin Labeling (CASL) measurements over a range of post-Labeling delay (PLD) times can be interpreted to estimate cerebral blood flow (CBF) and Arterial transit time (delta a) with good spatial and temporal resolution. In this work, we present an in vivo demonstration of Hadamard-encoded continuous Arterial Spin Labeling (H-CASL); an efficient method of imaging the inflow of short boli of labeled blood water in the brain at multiple PLO times. We present evidence that H-CASL is viable for in vivo application in the rat brain and can improve the precision of delta a estimation in 2/3 of the imaging time required for standard multi-PLD CASL. Based on these findings, we propose that H-CASL may have application as an efficient prescan for optimization of ASL imaging parameters to improve the precision of CBF estimation. Magn Reson Med 63:1111-1118, 2010. (C) 2010 Wiley-Liss, Inc.
