A CBF-based event-related brain activation paradigm: Characterization of impulse-response function and comparison to BOLD

A perfusion-based event-related functional MRI method for the study of brai n activation is presented. In this method, cerebral blood flow (CBF) was me asured using a recently developed multislice arterial spin-labeling (ASL) p erfusion imaging method with rapid spiral scanning. Temporal resolution of the perfusion measurement was substantially improved by employing intertria l subtraction and stimulus-shifting schemes. Perfusion and blood oxygenatio n level-dependent (BOLD) signals were obtained simultaneously by subtractin g or adding the control and labeled images, respectively, in the same data sets. The impulse response function (IRF) of perfusion during brain activat ion was characterized for multiple stimulus durations and compared to the s imultaneously acquired BOLD response. The CBF response curve preceded the B OLD curve by 0.21 s in the rising phase and 0.64 s in the falling phase. Li near additivity of the CBF and BOLD responses was assessed with rapidly rep eated stimulations within single trials, and departure from linearity was f ound in both responses, characterized as attenuated amplitude and delayed r ising time. Event-related visual and sensorimotor activation experiments we re successfully performed with the new perfusion technique, (C) 2000 Academ ic Press.