Imaging brain hemodynamic changes during rat forepaw electrical stimulation using functional photoacoustic microscopy

The present study reported the development of a novel functional photoacoustic microscopy (fPAM) system for investigating hemodynamic changes in rat cortical vessels associated with electrical forepaw stimulation. Imaging of blood optical absorption by fPAM at multiple appropriately-selected and distinct wavelengths can be used to probe changes in total hemoglobin concentration (HbT, i.e., cerebral blood volume [CBV]) and hemoglobin oxygen saturation (SO 2). Changes in CBV were measured by images acquired at a wavelength of 570 nm ( λ 570), an isosbestic point of the molar extinction spectra of oxy- and deoxy-hemoglobin, whereas SO 2 changes were sensed by pixel-wise normalization of images acquired at λ 560 or λ 600 to those at λ 570. We demonstrated the capacity of the fPAM system to image and quantify significant contralateral changes in both SO 2 and CBV driven by electrical forepaw stimulation. The fPAM system complements existing imaging techniques, with the potential to serve as a favorable tool for explicitly studying brain hemodynamics in animal models.