|Cerebral Perfusion: Arterial Spin Labelling|
Mapping Middle Cerebral Artery Branch Territories
with Vessel Encoded Pseudo-Continuous ASL: Sine/Cosine Tag Modulation
and Data Clustering in Tagging Efficiency Space
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.
Superselective Pseudo-Continuous Arterial Spin
Michael Helle1, 2, Matthias van Osch2, David Norris3, Karsten Alfke1, Olav Jansen1
1Christian-Albrechts-Universitšt, 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.
Single Artery Selective Labeling Using
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.
Selective Arterial Spin Labeling MRI Assessment of
the Contribution of the External Carotid Artery to Brain Perfusion in
Patients with Symptomatic Internal Carotid Artery Occlusion
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.
How Long to Tag? Optimal Tag Duration for Arterial
Spin Labeling at 1.5T, 3T, and 7T
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.
Can Arterial Spin Labeling Detect White Matter
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.
Water Exchange Rates in Grey and White Matter
Measured by Diffusion-Weighted 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.
Rapid Blood T1 Calibration for Arterial Spin Labelling
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 T1blood 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 T1blood 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 T1blood values obtained for adults are reproducible and in good agreement with existing literature.
A Comparative Study of Absolute Functional CBF
Measurements in Normal Human Brain Using PASL MRI and [O-15]water PET
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.
Is Arterial Spin Labeling Ready for Prime Time?
Preliminary Results from the QUASAR Reproducibility Study
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.