Fig. 6.

Matrix of average error in oxygenation for 26 wavelength pair combinations in 500- to 1000-nm range for different values of oxygenation in the tube, ${\mathrm{sO}}_2^{\text{tube}}$. In each figure, the bottom-left triangle represents ${\mathrm{sO}}_2$ estimates made with a spectrally varying background and the top-right triangle represent ${\mathrm{sO}}_2$ estimates made with a spectrally varying background using a depth-dependent fluence correction. The white pixels represent estimates with an error $>100\%$. In the regions marked “a,” this error is due to spectral coloring; in the regions marked “b,” it is due to poor conditioning. Top left: ${\mathrm{sO}}_2^{\text{tube}}=70\%$. Top right: ${\mathrm{sO}}_2^{\text{tube}}=80\%$. Bottom left: ${\mathrm{sO}}_2^{\text{tube}}=90\%$. Bottom right: ${\mathrm{sO}}_2^{\text{tube}}=100\%$.