Arterial spin labeling (ASL) is a magnetic resonance imaging (MRI)
method that provides a highly repeatable quantitative measure of cerebral
blood flow (CBF). As compared to the more commonly used blood oxygenation
level dependent (BOLD) contrast-based methods, ASL techniques measure a
more biologically specific correlate of neural activity, with the
potential for more accurate estimation of the location and magnitude of
neural function. Recent advances in acquisition and analysis methods have
improved the somewhat limited sensitivity of ASL to perfusion changes
associated with neural activity. In addition, ASL perfusion measures are
insensitive to the low-frequency fluctuations commonly observed in BOLD
experiments and can make use of imaging sequences that are less sensitive
than BOLD contrast to signal loss caused by magnetic susceptibility
effects. ASL measures of perfusion can aid in the interpretation of the
BOLD signal change and, when combined with BOLD, can measure the change in
oxygen utilization accompanying changes in behavioral state. Whether used
alone to probe neural activity or in combination with BOLD techniques, ASL
methods are contributing to the field's understanding of healthy and
disordered brain function. (JINS, 2007, 13,
517–525.)