Fig. 3.

${\mathrm{sO}}_2$ estimates using 26 wavelengths between 500 and 1000 nm. Top row: $x-z$ slice of error in oxygenation midway along tube’s length when the background is spectrally flat and the error originates from spectral coloring of the fluence in the blood-filled tube. Dashed lines used to indicate four $x-y$ slices (a–d) from which histograms of ${\mathrm{sO}}_2$ are formed (true value of 90% indicated by black line). Bottom row: $x-z$ slice of error in oxygenation midway along tube’s length when the background optical properties vary with wavelength. Both the cases with and without a depth-dependent fluence correction are shown. Dashed lines used to indicate four $x-y$ slices (a–d) from which histograms of ${\mathrm{sO}}_2$ are formed (true value of 90% indicated by vertical black line). (a–d) ${\mathrm{sO}}_2^{\text{mean}}$ represent the mean of the ${\mathrm{sO}}_2$ estimates of the voxels contained within the tube in slices a, b, c, and d, respectively, for the corrected data. The global mean ${\mathrm{sO}}_2^{\mathrm{g}.\text{mean}}$ of the corrected data, which represents ${\mathrm{sO}}_2$ estimates averaged over all voxels enclosed within the entire tube, is shown to the right of the histograms.