A qualitative test of the balloon model for BOLD-based MR signal changes at 3T

The aim of this study was to adapt the balloon model for BOLD‐based MR signal changes to a magnetic field strength of 3T and to examine its validity. The simultaneous measurement of BOLD and diffusion‐weighted BOLD responses was performed. The amplitude of the BOLD peak was found to be similar for all subjects when a short visual stimulus of 6 sec was used. The rise‐time to the BOLD peak and the shape and depth of the poststimulus undershoot varied significantly. A fit of the experimental BOLD responses was found to be possible by use of parameters within a reasonable physiological range. The relations between these parameters and their influence on the modeled BOLD responses is discussed. A prediction of the balloon model is the occurrence of a BOLD overshoot, i.e., a lag between the changes of the blood volume and the blood flow after the start of the stimulation. Experimental evidence for the existence of a BOLD overshoot is presented. Magn Reson Med 46:891–899, 2001. © 2001 Wiley‐Liss, Inc.