The Experts below are selected from a list of 12516 Experts worldwide ranked by ideXlab platform
Eric C Wong - One of the best experts on this subject based on the ideXlab platform.
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increased snr efficiency in velocity selective arterial Spin Labeling using multiple velocity selective saturation modules mm vsasl
Magnetic Resonance in Medicine, 2015Co-Authors: Jia Guo, Eric C WongAbstract:Purpose Velocity-selective arterial Spin Labeling (VSASL) is theoretically insensitive to transit delay (TD) effects. However, it uses saturation instead of inversion, resulting in compromised signal to noise ratio (SNR). In this study we explore the use of multiple velocity-selective saturation (VSS) modules in VSASL (mm-VSASL) to improve SNR.
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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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multiphase pseudocontinuous arterial Spin Labeling mp pcasl for robust quantification of cerebral blood flow
Magnetic Resonance in Medicine, 2010Co-Authors: Youngkyoo Jung, Eric C Wong, Thomas T LiuAbstract: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.
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vessel encoded arterial Spin Labeling using pseudocontinuous tagging
Magnetic Resonance in Medicine, 2007Co-Authors: Eric C WongAbstract:A new signal-to-noise ratio (SNR) efficient method is introduced for the mapping of vascular territories based on pseudocontinuous arterial Spin Labeling (ASL). A pseudocontinuous tagging pulse train is modified using additional transverse gradient pulses and phase cycling to place some arteries in a tag condition, while others passing through the same tagging plane are in a control condition. This is combined with a Hadamard or similar encoding scheme such that all vessels of interest are fully inverted or relaxed for nearly all of the encoding cycles, providing optimal SNR. The relative tagging efficiency for each vessel is measured directly from the ASL data and is used in the decoding process to improve the separation of vascular territories. High SNR maps of left carotid, right carotid, and basilar territories are generated in 6 min of scan time. Magn Reson Med, 2007. © 2007 Wiley-Liss, Inc.
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vessel encoded arterial Spin Labeling using pseudocontinuous tagging
Magnetic Resonance in Medicine, 2007Co-Authors: Eric C WongAbstract:A new signal-to-noise ratio (SNR) efficient method is introduced for the mapping of vascular territories based on pseudocontinuous arterial Spin Labeling (ASL). A pseudocontinuous tagging pulse train is modified using additional transverse gradient pulses and phase cycling to place some arteries in a tag condition, while others passing through the same tagging plane are in a control condition. This is combined with a Hadamard or similar encoding scheme such that all vessels of interest are fully inverted or relaxed for nearly all of the encoding cycles, providing optimal SNR. The relative tagging efficiency for each vessel is measured directly from the ASL data and is used in the decoding process to improve the separation of vascular territories. High SNR maps of left carotid, right carotid, and basilar territories are generated in 6 min of scan time.
David A Feinberg - One of the best experts on this subject based on the ideXlab platform.
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arterial Spin Labeling mri study of age and gender effects on brain perfusion hemodynamics
Magnetic Resonance in Medicine, 2012Co-Authors: David A Feinberg, Matthias Guenther, Johannes Gregori, Michael W Weiner, Norbert SchuffAbstract:Normal aging is associated with diminished brain perfusion measured as cerebral blood flow (CBF), but previously it is difficult to accurately measure various aspects of perfusion hemodynamics including: bolus arrival times and delays through small arterioles, expressed as arterial-arteriole transit time. To study hemodynamics in greater detail, volumetric arterial Spin Labeling MRI with variable postLabeling delays was used together with a distributed, dual-compartment tracer model. The main goal was to determine how CBF and other perfusion hemodynamics vary with aging. Twenty cognitive normal female and 15 male subjects (age: 23–84 years old) were studied at 4 T. Arterial Spin Labeling measurements were performed in the posterior cingulate cortex, precuneus, and whole brain gray matter. CBF declined with advancing age (P < 0.001). Separately from variations in bolus arrival times, arterial-arteriole transit time increased with advancing age (P < 0.01). Finally, women had overall higher CBF values (P < 0.01) and shorter arterial-arteriole transit time (P < 0.01) than men, regardless of age. The findings imply that CBF and blood transit times are compromised in aging, and these changes together with differences between genders should be taken into account when studying brain perfusion. Magn Reson Med, 2012. © 2011 Wiley Periodicals, Inc.
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minimizing acquisition time of arterial Spin Labeling at 3t
Magnetic Resonance in Medicine, 2008Co-Authors: Maria A Fernandezseara, Angela Hoang, Brian L. Edlow, David A Feinberg, Jiongjiong Wang, John A. DetreAbstract:An improved arterial Spin Labeling (ASL) perfusion technique that combines pseudo-continuous Labeling and a T2*-insensitive sequence (GRASE) with background suppression was used to acquire perfusion maps in normal volunteers and stroke patients. It is shown that perfusion measurements obtained in less than 1 min of scan time are reproducible, with a coefficient of variation of 7%. The perfusion maps generated from these data can be used to characterize the stroke lesion. Magn Reson Med 59:1467–1471, 2008. © 2008 Wiley-Liss, Inc.
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single shot 3d imaging techniques improve arterial Spin Labeling perfusion measurements
Magnetic Resonance in Medicine, 2005Co-Authors: Matthias Günther, Koichi Oshio, David A FeinbergAbstract:Arterial Spin Labeling (ASL) can be used to measure perfusion without the use of contrast agents. Due to the small volume fraction of blood vessels compared to tissue in the human brain (typ. 3–5%) ASL techniques have an intrinsically low signal-to-noise ratio (SNR). In this publication, evidence is presented that the SNR can be improved by using arterial Spin Labeling in combination with single-shot 3D readout techniques. Specifically, a single-shot 3D-GRASE sequence is presented, which yields a 2.8-fold increase in SNR compared to 2D EPI at the same nominal resolution. Up to 18 slices can be acquired in 2 min with an SNR of 10 or more for gray matter perfusion. A method is proposed to increase the reliability of perfusion quantification using QUIPSS II derivates by acquiring low-resolution maps of the bolus arrival time, which allows differentiation between lack of perfusion and delayed arrival of the labeled blood. For arterial Spin Labeling, single-shot 3D imaging techniques are optimal in terms of efficiency and might prove beneficial to improve reliability of perfusion quantitation in a clinical setup. Magn Reson Med 54:491–498, 2005. © 2005 Wiley-Liss, Inc.
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single shot 3d imaging techniques improve arterial Spin Labeling perfusion measurements
Magnetic Resonance in Medicine, 2005Co-Authors: Matthias Günther, Koichi Oshio, David A FeinbergAbstract:Arterial Spin Labeling (ASL) can be used to measure perfusion without the use of contrast agents. Due to the small volume fraction of blood vessels compared to tissue in the human brain (typ. 3-5%) ASL techniques have an intrinsically low signal-to-noise ratio (SNR). In this publication, evidence is presented that the SNR can be improved by using arterial Spin Labeling in combination with single-shot 3D readout techniques. Specifically, a single-shot 3D-GRASE sequence is presented, which yields a 2.8-fold increase in SNR compared to 2D EPI at the same nominal resolution. Up to 18 slices can be acquired in 2 min with an SNR of 10 or more for gray matter perfusion. A method is proposed to increase the reliability of perfusion quantification using QUIPSS II derivates by acquiring low-resolution maps of the bolus arrival time, which allows differentiation between lack of perfusion and delayed arrival of the labeled blood. For arterial Spin Labeling, single-shot 3D imaging techniques are optimal in terms of efficiency and might prove beneficial to improve reliability of perfusion quantitation in a clinical setup.
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, Amish D Patel, Kimiknu Mentore, Andrew A Wagner, Philip M Robson, Neil M Rofsky, Elizabeth M Genega, David C Alsop, 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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optimization of background suppression for arterial Spin Labeling perfusion imaging
Magnetic Resonance Materials in Physics Biology and Medicine, 2012Co-Authors: Nasim Maleki, Weiying Dai, David C AlsopAbstract:To present an algorithm for optimization of background suppression pulse timing for arterial Spin Labeling (ASL) perfusion imaging. An algorithm for optimization of background suppression pulse timing is proposed. Numerical optimization of timing of the background suppression pulses is investigated in both constrained and unconstrained ASL sequences. The performance of the parameters from the algorithm is evaluated in phantom and also in vivo in five human subjects. The background signal is suppressed to less than 1% across a broad range of T1s with a modest number of inversion pulses using the timings acquired from the numerical optimization algorithm proposed in this study. The performance of the parameters from the algorithm is also confirmed in vivo. Successful background suppression over a broad range of tissues is achievable. Values for optimal pulse timing in both pulsed and continuous ASL studies are reported to facilitate sequence design with different Labeling parameters.
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arterial Spin Labeling mr imaging for characterisation of renal masses in patients with impaired renal function initial experience
European Radiology, 2012Co-Authors: Andrew A Wagner, Ivan Pedrosa, Philip M Robson, Neil M Rofsky, Khashayar Rafatzand, Michael B Atkins, David C AlsopAbstract:Objectives To retrospectively evaluate the feasibility of arterial Spin Labeling (ASL) magnetic resonance imaging (MRI) for the assessment of vascularity of renal masses in patients with impaired renal function.
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, V.s. Basile, Christopher K. Macgowan, G Matta, Sandra E. Black, 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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skeletal muscle microvascular flow in progressive peripheral artery disease assessment with continuous arterial Spin Labeling perfusion magnetic resonance imaging
Journal of the American College of Cardiology, 2009Co-Authors: Emile R Mohler, John A. Detre, Felix W Wehrli, Sarah J Ratcliffe, Thomas F FloydAbstract:Objectives: We present the novel application of continuous arterial Spin-Labeling (CASL) magnetic resonance imaging (MRI) for the measurement of calf muscle perfusion in subjects with progressive p...
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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, Shannon C Agner, Stefanie E Mason, David W Silvestre, Daniel J. Licht, Sabrina E. Smith, Robert A. Zimmerman, Sumei Wang, John A. Detre, 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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minimizing acquisition time of arterial Spin Labeling at 3t
Magnetic Resonance in Medicine, 2008Co-Authors: Maria A Fernandezseara, Angela Hoang, Brian L. Edlow, David A Feinberg, Jiongjiong Wang, John A. DetreAbstract:An improved arterial Spin Labeling (ASL) perfusion technique that combines pseudo-continuous Labeling and a T2*-insensitive sequence (GRASE) with background suppression was used to acquire perfusion maps in normal volunteers and stroke patients. It is shown that perfusion measurements obtained in less than 1 min of scan time are reproducible, with a coefficient of variation of 7%. The perfusion maps generated from these data can be used to characterize the stroke lesion. Magn Reson Med 59:1467–1471, 2008. © 2008 Wiley-Liss, Inc.
Matthias Günther - One of the best experts on this subject based on the ideXlab platform.
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single shot 3d imaging techniques improve arterial Spin Labeling perfusion measurements
Magnetic Resonance in Medicine, 2005Co-Authors: Matthias Günther, Koichi Oshio, David A FeinbergAbstract:Arterial Spin Labeling (ASL) can be used to measure perfusion without the use of contrast agents. Due to the small volume fraction of blood vessels compared to tissue in the human brain (typ. 3-5%) ASL techniques have an intrinsically low signal-to-noise ratio (SNR). In this publication, evidence is presented that the SNR can be improved by using arterial Spin Labeling in combination with single-shot 3D readout techniques. Specifically, a single-shot 3D-GRASE sequence is presented, which yields a 2.8-fold increase in SNR compared to 2D EPI at the same nominal resolution. Up to 18 slices can be acquired in 2 min with an SNR of 10 or more for gray matter perfusion. A method is proposed to increase the reliability of perfusion quantification using QUIPSS II derivates by acquiring low-resolution maps of the bolus arrival time, which allows differentiation between lack of perfusion and delayed arrival of the labeled blood. For arterial Spin Labeling, single-shot 3D imaging techniques are optimal in terms of efficiency and might prove beneficial to improve reliability of perfusion quantitation in a clinical setup.
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single shot 3d imaging techniques improve arterial Spin Labeling perfusion measurements
Magnetic Resonance in Medicine, 2005Co-Authors: Matthias Günther, Koichi Oshio, David A FeinbergAbstract:Arterial Spin Labeling (ASL) can be used to measure perfusion without the use of contrast agents. Due to the small volume fraction of blood vessels compared to tissue in the human brain (typ. 3–5%) ASL techniques have an intrinsically low signal-to-noise ratio (SNR). In this publication, evidence is presented that the SNR can be improved by using arterial Spin Labeling in combination with single-shot 3D readout techniques. Specifically, a single-shot 3D-GRASE sequence is presented, which yields a 2.8-fold increase in SNR compared to 2D EPI at the same nominal resolution. Up to 18 slices can be acquired in 2 min with an SNR of 10 or more for gray matter perfusion. A method is proposed to increase the reliability of perfusion quantification using QUIPSS II derivates by acquiring low-resolution maps of the bolus arrival time, which allows differentiation between lack of perfusion and delayed arrival of the labeled blood. For arterial Spin Labeling, single-shot 3D imaging techniques are optimal in terms of efficiency and might prove beneficial to improve reliability of perfusion quantitation in a clinical setup. Magn Reson Med 54:491–498, 2005. © 2005 Wiley-Liss, Inc.
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comparison of arterial Spin Labeling techniques and dynamic susceptibility weighted contrast enhanced mri in perfusion imaging of normal brain tissue
Investigative Radiology, 2003Co-Authors: Marcandre Weber, Matthias Günther, Matthias P Lichy, Stefan Delorme, Andre Bongers, Christoph Thilmann, Marco Essig, I Zuna, Lothar R Schad, Jurgen DebusAbstract:Objectives:To evaluate relative cerebral blood flow (rCBF) in normal brain tissue using arterial Spin-Labeling (ASL) methods and first-pass dynamic susceptibility-weighted contrast-enhanced (DSC) magnetic resonance imaging (MRI).Methods:Sixty-two patients with brain metastases were examined on a 1.5
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quantification of blood flow in brain tumors comparison of arterial Spin Labeling and dynamic susceptibility weighted contrast enhanced mr imaging
Radiology, 2003Co-Authors: Carsten Warmuth, Matthias Günther, Claus ZimmerAbstract:PURPOSE: To implement an arterial Spin Labeling technique that is feasible in routine examinations and to test the method and compare it with dynamic susceptibility-weighted contrast material–enhanced magnetic resonance (MR) imaging for evaluation of tumor blood flow (TBF) in patients with brain tumors. MATERIALS AND METHODS: Thirty-six patients with histologically proven brain tumors were examined at 1.5 T. A second version of quantitative imaging of perfusion by using a single subtraction with addition of thin-section periodic saturation after inversion and a time delay (Q2TIPS) technique of pulsed arterial Spin Labeling in the multisection mode was implemented. After arterial Spin Labeling, a combined T2- and T2*-weighted first-pass bolus perfusion study (gadopentetate dimeglumine, 0.2 mmol/kg) was performed by using a double-echo echo-planar imaging sequence. In regions of interest, maps of absolute and relative cerebral blood flow were computed and analyzed with arterial Spin Labeling and dynamic sus...
