1Imaging, Lawson Health Research
Institute, London, ON, Canada; 2Medical Biophysics, University of
Western Ontario, London, ON, Canada; 3Radiology, University of
Pennsylvania, Philadelphia, PA, United States
The
arterial transit time (τa) and the exchange rate of water (kw) across
the blood-brain barrier were determined using diffusion-weighted arterial
spin labelling (ASL) with multiple post-labelling delay times. τa was
determined using bipolar gradients to suppress the arterial signal (i.e., the
FEAST method) and kw was determined using bipolar gradients strong enough to
suppress all vascular signals and a kinetic model to characterize water
exchange across the BBB. Averaged over four volunteers, kw was 119 min-1 in
grey matter and τa was 1.26 s. From repeat measurements, the
intra-subject coefficient of variation of kw was 12%.