Eric Wong¹, and Jia Guo^2
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.

Wen-Chau Wu^1,2
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.

Jia Guo¹, and Eric C. Wong^2
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.

John Robert Cain¹, Gerard Thompson¹, Laura M Parkes¹, and Alan Jackson^1
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.

Michael A Chappell^1,2, Bradley J MacIntosh^2,3, Mark W Woolrich², Peter Jezzard², and Stephen J Payne^1
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.

Wouter Teeuwisse¹, Michael Helle², Susanne Rüfer², and Matthias J P van Osch^1
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.

Yufen Chen¹, Ze Wang^1,2, and John A Detre^1
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.

Alan Jerry Huang^1,2, Jun Hua¹, Jonathan Farrell¹, Qin Qin¹, James J Pekar¹, Matthias van Osch³, John E Desmond⁴, and Peter van Zijl^5
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.

Deqiang Qiu¹, Michael E. Moseley¹, and Greg Zaharchuk^1
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.

Peiying Liu¹, Jinsoo Uh¹, Michael D Devous², Bryon Adinoff^3,4, and Hanzhang Lu^1
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.