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Time-encoded pseudo-continuous arterial spin labeling: Increasing SNR in ASL dynamic angiography

Woods, Joseph G.; Schauman, S. Sophie; Chiew, Mark; Chappell, Michael A.; Okell, Thomas W.


Joseph G. Woods

S. Sophie Schauman

Mark Chiew

Thomas W. Okell


Purpose: Dynamic angiography using arterial spin labeling (ASL) can provide detailed hemodynamic information. However, the long time-resolved readouts require small flip angles to preserve ASL signal for later timepoints, limiting SNR. By using time-encoded ASL to generate temporal information, the readout can be shortened. Here, the SNR improvements from using larger flip angles, made possible by the shorter readout, are quantitatively investigated. Methods: The SNR of a conventional protocol with nine Look-Locker readouts and a 4 (Formula presented.) 3 time-encoded protocol with three Look-Locker readouts (giving nine matched timepoints) were compared using simulations and in vivo data. Both protocols were compared using readouts with constant flip angles (CFAs) and variable flip angles (VFAs), where the VFA scheme was designed to produce a consistent ASL signal across readouts. Optimization of the background suppression to minimize physiological noise across readouts was also explored. Results: The time-encoded protocol increased in vivo SNR by 103% and 96% when using CFAs or VFAs, respectively. Use of VFAs improved SNR compared with CFAs by 25% and 21% for the conventional and time-encoded protocols, respectively. The VFA scheme also removed signal discontinuities in the time-encoded data. Preliminary data suggest that optimizing the background suppression could improve in vivo SNR by a further 16%. Conclusions: Time encoding can be used to generate additional temporal information in ASL angiography. This enables the use of larger flip angles, which can double the SNR compared with a non-time-encoded protocol. The shortened time-encoded readout can also lead to improved background suppression, reducing physiological noise and further improving SNR.


Woods, J. G., Schauman, S. S., Chiew, M., Chappell, M. A., & Okell, T. W. (2023). Time-encoded pseudo-continuous arterial spin labeling: Increasing SNR in ASL dynamic angiography. Magnetic Resonance in Medicine, 89(4), 1323-1341.

Journal Article Type Article
Acceptance Date Sep 23, 2022
Online Publication Date Oct 18, 2022
Publication Date 2023-04
Deposit Date Oct 28, 2022
Publicly Available Date Nov 1, 2022
Journal Magnetic Resonance in Medicine
Print ISSN 0740-3194
Electronic ISSN 1522-2594
Publisher Wiley
Peer Reviewed Peer Reviewed
Volume 89
Issue 4
Pages 1323-1341
Keywords Radiology, Nuclear Medicine and imaging
Public URL
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