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Eric C. Wong¹, Akash Kansagra¹

¹UC San Diego, La Jolla, California , USA

In vessel encoded pseudo-continuous ASL, vessels flowing through the tagging plane are differentially tagged and encoded.  Hadamard type encoding and a linear model are used to map perfusion territories.  In this work, we depart from the linear model and exploit the continuous nature of the spatial modulation of tagging to identify multiple vascular territories with a small number of encoding steps.  One method uses a sin/cos Fourier modulation technique, while the other uses data clustering in tagging efficiency space.  Territories of at least three branches of the M2 Segment of the MCA can be mapped using these methods.

Michael Helle¹, ², Matthias van Osch², David Norris³, Karsten Alfke¹, Olav Jansen¹

¹Christian-Albrechts-Universität, Kiel, Germany; ²Leiden University Medical Center, Leiden, Netherlands; ³FC Donders Centre for Cognitive Neuroimaging, Nijmegen, Netherlands

We introduce a modified tagging scheme based on pseudo-CASL that enables the labeling of single vessels. In this method the direction of additional transverse gradients is changed for every RF pulse in a random fashion. By adjusting the phase of the RF-pulses according to the applied extra gradients an efficient inversion results for the targeted vessel, whereas at other positions in the labeling plane phase variations avoid inversion. By increasing the strength of the added gradients, the labeling focus can be made more selective. Therefore this technique is capable of selectively labeling even small intracranial arteries.

Weiying Dai¹, ², Philip M. Robson¹, ², Ajit Shankaranarayanan³, David C. Alsop¹, ²

¹Beth Israel Deaconess Medical Center, Boston, Massachusetts, USA; ²Harvard Medical School, Boston, Massachusetts, USA; ³GE Healthcare, Menlo Park, California , USA

A method for single artery selective labeling is presented in which a disc around the targeted vessel is labeled. Based on pseudo-continuous labeling, this method is achieved by rotating the directions of the added in-plane gradients. Numerical simulations of the strategy show good efficiency but poor suppression of labeling at large distances. Addition of amplitude modulation of the in-plane gradients results in good suppression of distant vessels. In-vivo results demonstrates highly selective labeling of individual vessels and a rapid falloff of the perfusion signal as a function of distance between the center of the labeling disc and the carotid artery, in agreement with simulation results.

Jeroen Hendrikse¹, Jeroen Van der Grond², Peter Jan Van Laar³

¹UMC Utrecht, Utrecht, Netherlands; ²UMC Leiden, Netherlands; ³UMC Utrecht, Netherlands

The aim of the present study was to investigate the qualitative and quantitative contribution of the ipsilateral external carotid artery (ECA) to cerebral perfusion in patients with symptomatic ICA occlusion. Grading of the qualitative contribution of the ECA was performed with intraarterial DSA and the quantitative contribution was assessed with selective ASL MRI. We found that in patients with internal carotid artery (ICA) occlusion focal brain regions strongly depend on the contribution to cerebral perfusion of the ECA ipsilateral to the side of the ICA occlusion, even in patients with a limited ECA collateral supply on intraarterial digital subtraction angiography.

Wen-Ming Luh¹, Eric C. Wong², Peter A. Bandettini¹

¹National Institutes of Health, Bethesda, Maryland, USA; ²University of California, San Diego, La Jolla, California , USA

With the increase in field strength, higher SNR can be achieved for arterial spin labeling (ASL) because of increases in T1 values. The optimal duration of the tag will also increase with field strength; however, it becomes more difficult to achieve longer tag duration at higher field strength due to higher SAR for CASL and limited labeling coil size for PASL especially for whole brain coverage. In this paper, we estimated the optimal tag duration for 1.5T, 3T, and 7T for both techniques theoretically and verified the CASL results at 3T experimentally with pseudo-continuous ASL.

Wouter M. Teeuwisse¹, Marianne AA van Walderveen¹, Jeroen Hendrikse², Mark A. van Buchem¹, Jeroen van der Grond¹, Matthias Johannes Paulus van Osch¹

¹Leiden University Medical Center, Leiden, Netherlands; ²University Medical Center Utrecht, Utrecht, Netherlands

Recently there has been much discussion about the feasibility to image white matter perfusion by arterial spin labeling. Recent advances in ASL methodology, like pseudo-continuous ASL, have further increased SNR. Furthermore, velocity selective ASL is less sensitive to delay. In this abstract we show that for both pseudo continuous ASL and velocity selective ASL the majority of white matter voxels show signal that is statistically significant larger than 0. Finally, we show in a patient with an AVM the ability of ASL to identify regions in the WM of disturbed hemodynamics as proven by DSC perfusion MRI.

Keith St. Lawrence¹, ², Sumei Wang³, Wen-Chau Wu³, Maria A. Fernandez-Seara³, Jiongjiong Wang³

¹University of Western Ontario, London, Canada; ²Lawson Health Research Institute, London, Canada; ³University of Pennsylvania, Philadelphia, Pennsylvania, USA

The rate of water exchange (kw) across the blood-brain barrier was determined in grey and white matter regions using a diffusion-weighted arterial spin labelling (ASL) technique. Data were acquired at multiple post labelling delays to determine kw and the arterial transit time (ta) simultaneously. Averaged over five volunteers, kw was 181 and 262 min-1 in grey and white matter, respectively, and the corresponding ta values were 1.4 and 1.5 s. The kw in a developmental venous abnormality was shown to be lower than grey matter, which was attributed to the increased efflux of non-exchanged water into enlarged veins.

Marta Varela¹, Jo V. Hajnal¹, Esben Thade Petersen², ³, Xavier Golay², ⁴, David James Larkman¹

¹Robert Steiner MRI Unit, Hammersmith Hospital, Imperial College London, London, UK; ²National Neuroscience Institute, Singapore; ³Aarhus University Hospital, Aarhus, Denmark; ⁴Singapore Bioimaging Consortium, Singapore

The T₁ of blood is a critical parameter in perfusion quantification using Arterial Spin Labelling. It is believed that T_1blood may vary significantly within some patient and population groups, such as neonates, for whom ASL could constitute a valuable diagnostic tool. In this study, we introduce a method capable of rapidly measuring T_1blood in vivo and present results for both healthy adults and neonates acquired in less than 3 minutes per subject at 3T. We also show that T_1blood values obtained for adults are reproducible and in good agreement with existing literature.

Maolin Qiu¹, R P. Maguire², J Arora¹, B Planeta-Wilson¹, D Weinzimmer¹, N Rajeevan¹, R E. Carson¹, R T. Constable¹

¹Yale University School of Medicine, New Haven, Connecticut, USA; ²Pfizer, Groton, Connecticut, USA

This study is to validate multiple-slice CBF measurements by PASL against those measured by PET and to test reproducibility of PASL CBF measurements. The resting and activated state CBF was measured by PASL and task-induced changes in CBF were estimated in functionally and anatomically defined cortical regions. These values were compared to those measured in PET experiments using the same tasks in the same the subject group. Using the PASL protocol described in this study, the global resting CBF measured by PET and MR agrees; however discrepancies in local CBF were found. Task-induced CBF changes measured by PASL are larger than those by PET and this was observed over all ROIs inspected, regardless of how they were defined; this difference may be attributed to differences in the hemodynamic response times of the two modalities. PASL showed good reproducibility in CBF measurements.

Esben Thade Petersen¹, Xavier Golay, ¹², The QUASAR Reproducibility study

¹National Neuroscience Institute, Singapore, Singapore; ²Singapore Bioimaging Consortium, Singapore, Singapore

Arterial Spin Labeling is often portrayed as a perfusion tool only working in dedicated settings. In this work, we evaluated the QUASAR implementation in a test-retest worldwide. 22 centers and 199 subjects participated in this trial where each subject was scanned twice two weeks apart. Operator-independent slice-planning was performed using automatic planning tools. The accuracy of the slice-planning as well as the overall and in-between site reproducibility of ASL was tested. Good slice repositioning was achieved and the test-retest showed reasonable reproducibility across sites, suggesting that ASL is ready for use within and across centers in future clinical multi-centre studies.