Gottschalk, S. et al. Nat. Biomed. Eng. (2019).

Optoacoustics, which is also called photoacoustics, has been used to image hemodynamic activity in the brain. For this, the tissue is illuminated, and the light is then absorbed and converted into ultrasound waves, which can be recorded with acoustic transducers. In hemodynamic imaging, contrast is provided by hemoglobin, but alternative contrast agents can be used. In a recent paper, Gottschalk et al. extend previous work on optoacoustic imaging of the calcium sensor GCaMP5G in zebrafish. The researchers demonstrate that GCaMP6s and GCaMP6f can be imaged in the mouse despite potentially confounding hemodynamic contrast. In particular, calcium transients can be visualized when brief stimuli are used to elicit neural activity. Under these conditions, detectable hemodynamic responses are not evoked. In contrast, when longer stimuli are applied to the mouse, hemodynamic signals are dominant. The researchers demonstrate these findings in the context of electrical stimulation of the hind paw in anesthetized mice.