Signal-to-background ratio (SBR) in shallow and deep regions in three areas of the brain. a–c, Fluorescence intensity profiles along the lines across GCaMP6s-labeled neuronal nuclei (N=1 each). d–f, Fluorescence intensity profiles along the lines across blood vessels labelled with fluorescein (N=2 each). To produce each plot, a five-pixel-wide line was drawn across the blood vessel or nucleus. The 5 pixel values were averaged to get an intensity value for the corresponding position along the line. The x axis corresponds to the lines shown on the images to the right. Scale bar 50 μm.