Fig. 2.

Depth correction procedure demonstrated on the image of malignant lymph node (LN) M1. a) Uncorrected optoacoustic image ($\lambda$ = 700 nm) demonstrates the signal intensity decaying with depth. Only the top layer of the skin is visible, all other structures have too low intensity to be seen. The location of the LN and its 3 mm margin are denoted by dashed and dotted lines, respectively. b) Depth map. Pixels above the skin surface and inside the LN region are excluded. c) Map of median intensities. Each pixel shows the median intensity over all pixels in the image that are equally deep. Pixels in the LN region are excluded from the computation. As in (a), intensity decaying quickly with depth can be seen. d) Map of reciprocals to the median intensities shown in (c), which are used as multiplicative correction factors. e) Depth-corrected image, obtained by multiplying images (a) and (d), shows that the approach balances the signal intensities over the whole field of view.