Perfusion analysis using dynamic arterial spin labeling (DASL)

A variety of magnetic resonance (MR) techniques have proved useful to quant ify perfusion using endogenous water as a blood flow tracer. Assuming that water is a freely diffusable tracer, the model used for these techniques pr edicts that the quantitation of perfusion is based on three parameters, all of which can depend on blood flow. These are the longitudinal tissue relax ation time, the transit time from point of labeling to tissue, and the diff erence in tissue MR signal between an appropriate control and the labeled s tate. To measure these three parameters in parallel, a dynamic arterial spi n labeling (DASL) technique is introduced based on the analysis of the tiss ue response to a periodic time varying degree of arterial spin labeling, ca lled here the labeling function (LF), The LF frequency can be modulated to overdetermine parameters necessary to define the system. MR schemes are pro posed to measure the tissue response to different LF frequencies efficientl y. Sprague-Dawley rats were studied by DASL, using various frequencies for the LF and various arterial pCO(2) levels. During data processing, the peri odic behavior of the tissue response to the LF allowed for frequency filter ing of periodic changes in signal intensity unrelated to perfusion and arte rial spin labeling. Measures of transit time, tissue longitudinal relaxatio n time, and perfusion agreed well over a range of LF frequencies and with p revious results. DASL shows potential for more accurately quantifying perfu sion as well as measuring transit times associated with arterial spin label ing techniques. (C) 1999 Wiley-Liss, Inc.