Arterial Spin Labeling
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Thursday 10 May 2012
Plenary Hall  13:30 - 15:30 Moderators: David C. Alsop, Michael A. Chappell

13:30 0574.   High Resolution Mouse Kidneys Perfusion Imaging using Pseudocontinuous ASL (pCASL) at Very High Field (11.75T)
Guillaume Duhamel1, Virginie Callot1, and Patrick J. Cozzone1
1CRMBM, UMR 6612, CNRS, Aix-Marseille University, Marseille, France

Reliable assessment of the kidneys microvascular perfusion would be very valuable for many renal diseases which have shown to be linked to damage or loss of renal microvessels. Arterial Spin Labeling, despite its low sensitivity, had shown great potential for quantification of renal blood flow (RBF), by offering a simple quantification model and a blood contrast specificity without any contrast agent injection. This work presents the application of the highly sensitive pseudocontinuous ASL (pCASL) technique at 11.75T for high resolution mouse renal perfusion measurement.

13:42 0575.   
Noninvasive characterization of lymphatic flow velocity using principles of spin labeling permission withheld
Swati Rane1, Paula Donahue2, John Jordi3, John C Gore1,4, and Manus Donahue1
1Radiology and Radiological Sciences, Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, TN, United States, 2Vanderbilt-Ingram Cancer Center, Vanderbilt University, Nashville, TN, United States, 3Lymphedema Clinic, Siskin Hospital, Chattanooga, TN, United States,4Biomedical Engineering, Vanderbilt University, Nashville, TN, United States

The aim of this study is to exploit principles of spin labeling to magnetically label water in human lymphatic fluid and for the first time noninvasively characterize the flow of lymphatic fluid to lymph nodes. We report quantitative measures of 3T lymphatic T1 (3117158 ms) and T2 (60512 ms) and use pulsed spin labeling principles in conjunction with parallel-transmit technology to quantify lymphatic flow velocity (5.9 cm/min) in healthy volunteers. Results outline the potential for lymphedema risk to be assessed in patients following axillary node removal by identifying and monitoring the compromised lymphatic flow patterns in preclinical stages of disease.

13:54 0576.   
Impact of eddy currents on quantification of perfusion using Velocity Selective Arterial Spin Labeling
James Alastair Meakin1,2, and Peter Jezzard1
1FMRIB Centre, University of Oxford, Oxford, United Kingdom, 2Gray Institute for Radiation Oncology and Biology, University of Oxford, Oxford, United Kingdom

Inaccurate measurement of perfusion using VSASL can arise due to the sensitivity of the velocity selective preparation to eddy currents. In this study, three velocity selective preparations were evaluated: a Double Refocused Hyperbolic Secant, BIR-4 and a novel BIR-8 preparation. We show that eddy currents during the velocity selective preparation cause unwanted tagging of static tissue and an overestimation of perfusion in VSASL. We demonstrate through simulations and experiments in healthy volunteers that the BIR-8 preparation has the least sensitivity to eddy currents, providing more accurate VSASL perfusion measurements.

14:06 0577.   
Acceleration Selective Arterial Spin Labeling
Sophie Schmid1, Eidrees Ghariq1, Wouter M. Teeuwisse1, Andrew Webb1, and Matthias J.P. van Osch1,2
1C.J. Gorter Center for High Field MRI, Dept. of Radiology, Leiden University Medical Center, Leiden, Netherlands, 2Leiden Institute of Brain and Cognition, Leiden, Netherlands

As opposed to Velocity Selective Arterial Spin Labeling (ASL), which labels both arterial and venous blood, a new ASL technique is demonstrated, called AccASL, which labels flowing spins based on acceleration. It has been shown that the proposed AccASL is a promising method to enable measurement of the perfusion with spatially non-selective labeling, elimination of venous label and high signal intensity in grey matter.

14:18 0578.   Retinotopic maps and hemodynamic delays in the human visual cortex measured using arterial spin labeling
Mustafa Cavusoglu1,2, Andreas Bartels3, and Kamil Uludag4
1Biomedical Engineering, ETH Zurich, Zurich, Switzerland, 2High Field MR Center, Max Planck Institute, Tuebingen, Germany, 3Vision and Cognition lab, Center for Integrative Neuroscience, Tuebingen, Germany, 4Department of Cognitive Neuroscience, Maastricht Brain Imaging Centre (MBIC), Maastricht, Netherlands


14:30 0579.   
Volumetric Measurement of Perfusion and Arterial Transit Delay Using Hadamard Encoded Continuous Arterial Spin Labeling
Weiying Dai1, Ajit Shankaranarayanan2, and David Alsop1
1Radiology, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, United States, 2Global Applied Science Laboratory, GE Healthcare, Menlo Park, United States

Hadamard encoded arterial spin labeling techniques have been proposed to increase the SNR and time efficiency of multiple delay methods for arterial transit delay (ATD) measurement. Here, we report methods for robust Hadamard encoded CASL with volumetric acquisition in humans. The SNR of the Hadamard encoded measurements of ATD and perfusion were compared to more standard acquisitions. Hadamard encoded ASL provided the most sensitive measure of ATD, but its sensitivity for perfusion was approximately half that of CASL acquisitions when ATD is known or assumed.

14:42 0580.   
Implementation and validation of time encoded pseudo Continuous Arterial Spin Labelling for human applications.
Wouter M Teeuwisse1, Ilya M Veer2, Andrew Webb1, and Matthias J.P. van Osch1
1C.J.Gorter Center for High Field Magnetic Resonance, Radiology, Leiden University Medical Center, Leiden, ZH, Netherlands, 2Radiology, Leiden University Medical Center, Leiden, ZH, Netherlands

In this study, time encoded pCASL is implemented on a clinical 3T scanner. Following a Hadamard encoding scheme, pCASL is modified such that the labelling period is split into blocks with varying label/control condition. This enables calculation of perfusion maps with 11 different post labelling delays from a single scan. Two versions were evaluated, one with blocks of constant duration and one with block duration adjusted for T1 decay of labelling signal. Resulting, whole brain, perfusion maps clearly show local and global variation in arterial filling and tissue enhancement over time. Quantitative ATT maps demonstrate the flow territory border zones.

14:54 0581.   Vessel Encoded Arterial Spin Labeling using Fourier Encoding
Youngkyoo Jung1,2
1Radiology, Wake Forest School of Medicine, Winston-Salem, NC, United States, 2Biomedical Engineering, Wake Forest School of Medicine, Winston-Salem, NC, United States

PCASL-based VE-ASL methods often require long scan times and complicated clustering algorithms to classify multiple vascular territories. VE-ASL can be performed by encoding blood signal in the Fourier space based on the source location. We have demonstrated that the proposed Fourier encoding method allows quantitative vascular territory mapping without knowledge of accurate locations of feeding arteries or complicated post-processing algorithm. In addition, the method is immune to phase errors due to resonance offsets and can be performed within clinically relevant scan time (<4min).

15:06 0582.   
Visualizing Artery-specific Blood Flow Patterns Above the Circle of Willis with Vessel-Encoded Arterial Spin Labeling
Thomas W Okell1, Michael A Chappell1,2, and Peter Jezzard1
1FMRIB Centre, Department of Clinical Neurosciences, University of Oxford, Oxford, Oxfordshire, United Kingdom, 2Institute of Biomedical Engineering, Department of Engineering, University of Oxford, Oxford, Oxfordshire, United Kingdom

Vessel-encoded pseudocontinuous arterial spin labeling (VEPCASL) is typically used to generate artery-specific perfusion maps of three or four brain-feeding arteries. The ability to label a larger number of vessels may be useful for assessing flow patterns in smaller arteries, such as those supplying an arteriovenous malformation. Here we encode thirteen arteries (nine intracranial, four extracranial) above the circle of Willis in healthy volunteers using both dynamic angiographic and perfusion-weighted readouts. The Bayesian analysis method used successfully separates all vascular components. The resulting artery-specific images reveal blood flow patterns and hemodynamics within the vessels along with the resulting downstream perfusion.

15:18 0583.   
Improved estimation of cerebral artery branch territories using cluster-based segmentation of vessel-encoded pseudocontinuous ASL data
Akash P Kansagra1, and Eric C Wong2
1Radiology and Biomedical Imaging, UC San Francisco, San Francisco, CA, United States, 2Radiology and Psychiatry, UC San Diego, San Diego, CA, United States

Vessel encoded pseudo-continuous ASL allows non-invasive estimation of multiple cerebrovascular territories above the circle of Willis. Segmentation of vascular territories has traditionally been achieved by clustering of highly correlated tagging data. Here, we assess improvements in vascular territory estimation that occur when tagging efficiency data are supplemented with spatial data in the clustering scheme. These results offer a simple and straightforward means to enhance the accuracy of mapping of small cerebral artery branch territories.