Functional photoacoustic micro-imaging of rat cerebral hemodynamic response function in single vessels during forepaw electrical stimulation

The specificity of the hemodynamic response function (HRF) is determined spatially by the vascular architecture and temporally by the evolution of hemodynamic changes. Here, we used functional photoacoustic microscopy (fPAM) to investigate the spatiotemporal evolution of the HRFs of hemoglobin concentration (HbT), cerebral blood volume (CBV) and hemoglobin oxygen saturation (SO2) in single cerebral vessels to rat left-forepaw stimulation. The HRF changes in specific cerebral vessels responding to different stimulation intensities and durations were bilaterally imaged with 36 x 65-mu m spatial resolution. Various electrical stimulations were applied with stimulation intensities at 1, 2, 6 and 10-mA combined with 5-s and 15-s stimulation durations, respectively. Our main findings were as follows: 1) the functional HbT and SO2 increased sub-linearly with increasing stimulus intensities and 2) the results suggested that the CBV changes are more linearly correlated with arterioles than HbT and SO2 within a limited dynamic range of stimulation intensities and duration. The findings in this study indicate that the regulation of hemodynamic changes in single cerebral vessels can be reliable studied by the fPAM technique without the use of contrast agents.