Modeling and optimization of look‐locker spin labeling for measuring perfusion and transit time changes in activation studies taking into account arterial blood volume

Abstract

This work describes a new compartmental model with step‐wise temporal analysis for a Look‐Locker (LL)‐flow‐sensitive alternating inversion‐recovery (FAIR) sequence, which combines the FAIR arterial spin labeling (ASL) scheme with a LL echo planar imaging (EPI) measurement, using a multireadout EPI sequence for simultaneous perfusion and T measurements. The new model highlights the importance of accounting for the transit time of blood through the arteriolar compartment, δ, in the quantification of perfusion. The signal expected is calculated in a step‐wise manner to avoid discontinuities between different compartments. The optimal LL‐FAIR pulse sequence timings for the measurement of perfusion with high signal‐to‐noise ratio (SNR), and high temporal resolution at 1.5, 3, and 7T are presented. LL‐FAIR is shown to provide better SNR per unit time compared to standard FAIR. The sequence has been used experimentally for simultaneous monitoring of perfusion, transit time, and T changes in response to a visual stimulus in four subjects. It was found that perfusion increased by 83 ± 4% on brain activation from a resting state value of 94 ± 13 ml/100 g/min, while T increased by 3.5 ± 0.5%. Magn Reson Med 2007.