Arterial Spin Labeling
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Tuesday May 10th
Room 512A-G  16:00 - 18:00 Moderators: David Alsop and Wen-Chau Wu

16:00 294.   Blind Detection of Source Vessel Locations and Resonance Offsets using Randomly Encoded VEASL 
Eric Wong1, and Jia Guo2
1Radiology/Psychiatry, UC San Diego, La Jolla, CA, United States, 2Bioengineering, UC San Diego, La Jolla, CA, United States

In Vessel Encoded ASL (VEASL), arteries in the tagging plane are encoded in a pseudo-continuous ASL tagging scheme to allow for the identification of vascular territories.  Resonance offsets in the tagging plane reduce tagging efficiency and can be alleviated using multiphase approaches.  In this work, we introduce the use of random encoding to simultaneously encode and identify both the vessel locations and resonance offsets with high efficiency and without any prior knowledge.  We expect that this approach will be useful when collateral or variant circulation may be present, and resonance offsets significant.

16:12 295.   Mapping cerebral blood flow territories using harmonic encoding pseudocontinuous arterial spin labeling, fuzzy clustering, and independent component analysis 
Wen-Chau Wu1,2
1Graduate Institute of Oncology, National Taiwan University, Taipei, Taiwan, 2Graduate Institute of Clinical Medicine, National Taiwan University, Taipei, Taiwan

Vessel-encoded pseudocontinuous arterial spin labeling (VEPCASL) is a novel MRI technique with capability of differentiating flow territories of the primary arteries passing through a predefined tagging plane. We implemented VEPCASL with harmonic encoding to expand feature dimension and employed ICA and FCM clustering for territory separation. Results have shown that ICA and FCM substantially improve the robustness of K-means clustering. Feature dimension can be efficiently expanded using harmonic encoding, especially along the direction where vascular branches are more complex. FCM may depict the borderline of two or more flow territories and provide useful information for clinical evaluation of watershed infarction.

16:24 296.   Increased Tagging Efficiency in Velocity Selective ASL using Multiple Velocity Selective Saturation Modules 
Jia Guo1, and Eric C. Wong2
1Bioengineering, University of California San Diego, La Jolla, California, United States, 2Department of Radiology and Psychiatry, University of California San Diego, La Jolla, California, United States

In VSASL, arterial blood is tagged by velocity selective saturation (VSS). This method is inherently insensitive to transit delays and may be useful in applications where transit delay can be long, such as white matter and in stroke. In this work, we note that by using two or more VSS modules, T1 decay of the tag can be reduced, increasing the overall tagging efficiency and hence the SNR of VSASL. Dual VSS VSASL was implemented and tested in human volunteers, and the measured signal was approximately 40% higher using 2 VSS modules, in good agreement with theory.

16:36 297.   Arrival Time Changes Demonstrate Active Cerebral Autoregulation in Normal Subjects using Lower Body Negative Pressure and Arterial Spin Labeling MRI 
John Robert Cain1, Gerard Thompson1, Laura M Parkes1, and Alan Jackson1
1Imaging Science, University of Manchester, Manchester, United Kingdom

Cerebral autoregulation maintains cerebral perfusion during varying cardiac outputs. We present MRI perfusion data demonstrating active cerebral autoregulation. We constructed an MRI compatible lower body negative pressure (LBNP) chamber and investigated its effects on cerebral perfusion and bolus arrival time (BAT) using arterial spin labeling. Ten volunteers (24-31years) underwent MRI during the control state and -20mmHg LBNP. -20mmHg LBNP reduced cardiac output by 0.5l/min. No difference between grey matter (GM) perfusion was found between control and -20mmHg LBNP. GM BAT was delayed during -20mmHg LBNP. The BAT delay suggests -20mmHg LBNP causes autoregulatory mechanisms to dilate vessels maintaining GM perfusion.

16:48 298.   Modelling dispersion in Arterial Spin Labelling with Validation from ASL Dynamic Angiography 
Michael A Chappell1,2, Bradley J MacIntosh2,3, Mark W Woolrich2, Peter Jezzard2, and Stephen J Payne1
1Institute of Biomedical Engineering, University of Oxford, Oxford, United Kingdom, 2FMRIB Centre, University of Oxford, Oxford, United Kingdom, 3Department of Medical Biophysics, University of Toronto, Toronto, Ontario, Canada

The dispersion of the labelled bolus in Arterial Spin Labeling (ASL) has a substantial effect on the quantification of cerebral blood flow. A number of models exist to account for dispersion effects. However, the comparison and validation of these models is difficult using the conventional perfusion signal. Here data from an ASL preparation coupled with a dynamic angiographic readout is used to capture signal whilst blood is still within the arteries. A ‘Goodness-of-fit’ metric for the different models is compared and models based on a vascular transport function with an asymmetric kernel appear to be most accurate.

17:00 299.   Cardiac triggering and label-control transition profiles in Hadamard encoded pseudo-continuous arterial spin labeling 
Wouter Teeuwisse1, Michael Helle2, Susanne Rüfer2, and Matthias J P van Osch1
1Radiology, C.J. Gorter Center for High Field MRI, Leiden University Medical Center, Leiden, Netherlands, 2Institute for Neuroradiology, Christian-Albrechts-Universität, UK-SH, Kiel, Germany

Hadamard encoded continuous ASL is a promising technique to obtain dynamic ASL angiography images and temporal information such as transport delay time in a short scan time. However blurring of the encoding pattern by the cardiac cycle and non instantaneous switching between label and control can hamper the efficacy. By means of simulations and in vivo experiments, the necessity of cardiac triggering is shown and a minimum switching time of 50 ms for pCASL is demonstrated.

17:12 300.   Impact of equilibrium magnetization of blood on ASL quantification 
Yufen Chen1, Ze Wang1,2, and John A Detre1
1Center for Functional Neuroimaging, University of Pennsylvania, Philadelphia, PA, United States, 2Department of Psychiatry, University of Pennsylvania, Philadelphia, PA, United States

The equilibrium magnetization of blood (M0b) is an important factor for ASL quantification that is difficult to measure due to the low image resolution. In this study, we compared the quantification results of map-based and ratio-based M0b estimates. Although the gray matter cerebral blood flow (CBF) estimates were similar, map-based M0b reduced the gray to white matter contrast of the CBF maps unless tissue-specific partition coefficients are used. Ratio-based M0b methods are preferred but require accurate T2* and coil sensitivity correction for accurate CBF quantification.

17:24 301.   Quantification of Cerebellar Blood Flow using Arterial Spin Labeling 
Alan Jerry Huang1,2, Jun Hua1, Jonathan Farrell1, Qin Qin1, James J Pekar1, Matthias van Osch3, John E Desmond4, and Peter van Zijl5
1FM Kirby Research Center, Johns Hopkins University, Baltimore, MD, United States, 2Department of Biomedical Engineering, Johns Hopkins University, Baltimore, MD, United States, 3Department of Radiology, Leiden University Medical Center, Leiden, Netherlands, 4Department of Neurology, Johns Hopkins University, Baltimore, MD, United States, 5FM Kirby Research Center, Johns Hopkins University, Baltimore

The cerebellum is an important part of the brain responsible for motor functions, sensory control, and cognitive function. Arterial spin labeling (ASL) is a non-invasive, non-ionizing technique that allows for repetitive measurements of perfusion. The location of the cerebellum allows for access of labeled spins to reach the cerebellum quickly allowing for higher temporal resolution of ASL scans. We report an average cerebellar gray matter perfusion value of 63.6±5.0 mL/100 g parenchyma/min for three healthy subjects.

17:36 302.   Comparison of Pseudocontinuous and Velocity Selective Arterial Spin Labeling with Gold Standard Xenon CT: a Study in Patients with Moyamoya Disease 
Deqiang Qiu1, Michael E. Moseley1, and Greg Zaharchuk1
1Lucas Imaging Center, Stanford University, Stanford, CA, United States

In this study, we compared the performance of 3D-FSE pseudocontinuous arterial spin labeling (pcASL) acquired at multiple post-label delay times and velocity-selective ASL (VSASL) in Moyamoya disease patients, who have known arterial transit arrival delay due to collateral networks. Stable xenon CT perfusion served as a CBF gold standard. Mean CBF differences and correlations were determined and compared. VSASL was shown to provide relatively more accurate absolute measurement of CBF values, though its correlation with xeCT measurement is not as strong as for pcASL due to overall lower SNR.

17:48 303.   SPECT Validation of Pseudo-continuous Arterial Spin Labeling MRI 
Peiying Liu1, Jinsoo Uh1, Michael D Devous2, Bryon Adinoff3,4, and Hanzhang Lu1
1Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, United States, 2Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States, 3Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, Texas, United States,4VA North Texas Health Care System, Dallas, Texas, United States

Pseudo-continuous Arterial Spin Labeling (PCASL) as a new arterial spin labeling (ASL) technique has shown great promises in terms of sensitivity and practicality. Validation of this technique with a gold-standard method would provide a critical step toward wider applications in neurological and brain mapping studies. Here we first determined the arterial transit times which are important in the quantification of CBF from ASL signals by measuring the time difference between the appearance of Gd-DTPA bolus in the labeling and imaging slices, respectively. We then conducted a validation study of PCASL using a radiotracer-based single photon emission computer tomography (SPECT) method.