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A theoretical and experimental investigation of the tagging efficiency of pseudocontinuous arterial spin labeling
Author(s) -
Wu WenChau,
FernándezSeara María,
Detre John A.,
Wehrli Felix W.,
Wang Jiongjiong
Publication year - 2007
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.21403
Subject(s) - arterial spin labeling , computer science , nuclear magnetic resonance , steady state free precession imaging , offset (computer science) , physics , magnetic resonance imaging , medicine , radiology , programming language
Arterial spin labeling (ASL) is capable of noninvasively measuring blood flow by magnetically tagging the protons in arterial blood, which has been conventionally achieved using instantaneous (PASL) or continuous (CASL) RF pulses. As an intermediate method, pseudocontinuous ASL (pCASL) utilizes a train of discrete RF pulses to mimic continuous tagging that is often unavailable on imagers due to the requirement of continuous RF transmit capabilities. In the present study, we implemented two versions of pCASL ( balanced and unbalanced gradient waveforms in tag and control scans) for both transmit/receive coils and array receivers. Experimental data show a 50% ± 4% increase of signal‐to‐noise ratio (SNR) compared with PASL and a higher tagging efficiency than amplitude‐modulated (AM) CASL (80% vs. 68%). Computer simulations predict an optimal tagging efficiency of 85% for flow velocities from 10 to 60 cm/s. It is theoretically and experimentally demonstrated that the tagging efficiency of pCASL is dependent upon the resonance offset and flip angle of the RF pulse train. We conclude that pCASL has the potential of combining the merits of PASL, including less hardware demand and higher tagging efficiency, and CASL, which includes a longer tagging bolus and thus higher SNR. These improvements provide a better balance between tagging efficiency and SNR. Magn Reson Med 58:1020–1027, 2007. © 2007 Wiley‐Liss, Inc.