Fig. 3.

Contrast and penetration depth enhancement in microscopy of ex vivo liver tissue. (A) We labeled the Kupffer cells of a mouse liver using a broadly emitting quantum dot emulsion, and imaged the cells via microscopy with 50-nm band-pass emission filters centered across SWIR wavelengths, a subset of which are shown here at imaging depths of 40, 70, and 100 μm for 1,000-, 1,200-, 1,450-, and 1,600-nm filters. Integration times for all images are listed in SI Appendix, Table S1. All images are set to fill the maximum displayable intensities. (Scale bar, 200 μm.) (B) The contrast, $c_V$ (Eq. 1), was calculated and plotted as a function of wavelength (black line) for images taken at a depth of 40 μm. The contrast shows a similar trend to the water absorptance spectrum (blue line). (C) Furthermore, penetration depth was calculated using an algorithm adapted from Rowlands et al. (38) and plotted as a function of wavelength, showing a similar trend. The dashed lines mark the depths at which the images in A were taken, and the crosses display the wavelength positions. Green boxes and crosses indicate images considered to be resolvable within the contrast threshold.