Fig. 5.

Spectral triangulation scheme and results. (a) Measured spectral shapes depend on probe position, reflecting different average path lengths from source to probe through tissue. Analysis of spectral ratios from several probe positions gives coordinates of source. (b) Errors in the x- and y-coordinates deduced by spectral triangulation of an emission source at three different source depths. The separation between horizontal dashed lines indicates the diameter of the source, and error bars show standard deviations of replicate determinations. For each triangulation, twenty grid points were measured with 2 filters at each point and 2 s acquisitions, giving a total measurement time below 3 min including probe positioning. (c) Source depth coordinates deduced from spectral triangulation are plotted vs. actual depth. Dashed lines mark the boundaries of the source, and error bars show standard deviations.