Voxel intensity histograms (3D) of the masked sLS volumes from a , c , e , g , i (that is, summed intensity inside masks) showing the distribution of the scattered signal on logarithmic ( l ) (16-bit) axes. While background distributions in l vary for different mask volumes, pink and green curves (nanobots in urea) correlate with MIP images in a , b , g , h , with a long high-intensity tail indicating a prominent signal; in other conditions (without nanobots or with nanobots in water) intensity drops off quickly with no counts above intensities of about 7,000. In g , the cavity inside the bladder was too thin and collapsed to be segmented, hence the mask includes the full volume (including the lumen), although residual cavity background does not contribute to the high intensities.
