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Scientific article
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Depth sensitivity of frequency domain optical measurements in diffusive media

Published inBiomedical Optics Express, vol. 8, no. 6, p. 2990-3004
Publication date2017
Abstract

The depth sensitivity functions for AC amplitude, phase (PH) and DC intensity signals have been obtained in the frequency domain (where the source amplitude is modulated at radio-frequencies) by making use of analytical solutions of the photon diffusion equation in an infinite slab geometry. Furthermore, solutions for the relative contrast of AC, PH and DC signals when a totally absorbing plane is placed at a fixed depth of the slab have also been obtained. The solutions have been validated by comparisons with gold standard Monte Carlo simulations. The obtained results show that the AC signal, for modulation frequencies < 200 MHz, has a depth sensitivity with similar characteristics to that of the continuous-wave (CW) domain (source modulation frequency of zero). Thus, the depth probed by such a signal can be estimated by using the formula of penetration depth for the CW domain (Sci. Rep.6, 27057 (2016)). However, the PH signal has a different behavior compared to the CW domain, showing a larger depth sensitivity at shallow depths and a less steep relative contrast as a function of depth. These results mark a clear difference in term of depth sensitivity between AC and PH signals, and highlight the complexity of the estimation of the actual depth probed in tissue spectroscopy.

Citation (ISO format)
BINZONI, Tiziano et al. Depth sensitivity of frequency domain optical measurements in diffusive media. In: Biomedical Optics Express, 2017, vol. 8, n° 6, p. 2990–3004. doi: 10.1364/BOE.8.002990
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ISSN of the journal2156-7085
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