Simultaneous blood oxygenation level-dependent and cerebral blood flow functional magnetic resonance imaging during forepaw stimulation in the rat

The blood oxygenation level-dependent (BOLD) contrast mechanism can be mode led as a complex interplay between CBF, cerebral blood volume (CBV), and CM RO2. Positive BOLD signal changes are presumably caused by CBF changes in e xcess of increases in CMRO2. Because this uncoupling between CBF and CMRO2 may not always be present, the magnitude of BOLD changes may not be a good index of CBF changes. In this study, the relation between BOLD and CBF was investigated further. Continuous arterial spin labeling was combined with a single-shot, multislice echo-planar imaging to enable simultaneous measure ments of BOLD and CBF changes in a well-established model of functional bra in activation, the electrical forepaw stimulation of alpha-chloralose-anest hetized rats. The paradigm consisted of two 18- to 30-second stimulation pe riods separated by a 1-minute resting interval. Stimulation parameters were optimized by laser Doppler flowmetry. For the same cross-correlation thres hold, the BOLD and CBF active maps were centered within the size of one pix el (470 mu m). However, the BOLD map was significantly larger than the CBF map. Measurements taken from 15 rats at 9.4 T using a 10-millisecond echo-t ime showed 3.7 +/- 1.7% BOLD and 125.67 +/- 81.7% CBF increases in the cont ralateral somatosensory cortex during the first stimulation, and 2.6 +/- 1. 2% BOLD and 79.3 +/- 43.6% CBF increases during the second stimulation The correlation coefficient between BOLD and CBF changes was 0.89. The overall temporal correlation coefficient between BOLD and CBF time-courses was 0.97 . These results show that under the experimental conditions of the current study, the BOLD signal changes follow the changes in CBF.