Optimal spectral acquisition band for temperature profiling in human skin using pulsed photothermal radiometry

We studied pulsed photothermal radiometric temperature profiling in human skin in numerical simulations. We considered two detectors with different spectral responses (InSb, 3.0 - 5.3 &mgr;m; HgCdTe, 5.0 - 12.0 &mgr;m). By taking into account sensitivity of available radiation detectors, realistic noise, blackbody emission characteristics and spectral variation of human skin IR absorption coefficient for a certain acquisition band, we computed realistic PPTR signals for analytical temperature profiles (Hyper-Gaussian, 100 - 500 &mgr;m deep). For each spectral band we determined the optimal effective monochromatic absorption coefficient to be used in reconstructions. We reconstructed temperature profiles from the simulated signals using a custom code, based on the conjugate-gradient algorithm and including automatic adaptive regularization. Quantitative analysis of the reconstructed temperature profiles enables determination of optimal spectral acquisition band for each IR detector. In case of InSb detector, narrow acquisition bands yield lower reconstruction errors for shallow objects, but wide acquisition bands are preferred for deeper objects. The 4.1 - 5.6 &mgr;m spectral band offers a good compromise for objects placed at variable depths. For the HgCdTe detector the results indicate that optimal acquisition spectral band is 6.4 - 12.0 µm. The results also suggest that HgCdTe detector used at 6.4 - 12.0 µm performs better than InSb detector used at 4.1 - 5.6 &mgr;m.