Effect of skin and fat layers on the spatial sensitivity profile of continuous wave diffuse reflectance near-infrared spectra

In order to measure muscle physiological parameters such as pH and oxygen partial pressure (PO2) by continuous wave (CW) diffuse reflectance near-infrared spectroscopy (NIRS), light must penetrate through skin and subcutaneous fat layers overlying muscle. In this study, the effect of skin and subcutaneous fat layer and on the spatial sensitivity profile of CW diffuse reflectance near-infrared spectra is investigated through Monte Carlo simulations. The simulation model uses a semi-infinite medium consisting of skin, fat and muscle. The optical properties of each layer are taken from the reported optical data at 750 nm. The skin color is either Caucasian or Negroid and the fat thickness is varied from 0 ~ 20 mm. The spatial sensitivity profile, penetration depth, and sensitivity ratio as functions of optical fiber source-detector separation (SD, 2.5 mm, 5.0 mm, 10.0 mm, 20.0 mm, 30.0 mm and 40.0 mm), skin color and fat thicknesses are predicted by the simulations. It is shown that skin color only slightly influenced the spatial sensitivity profile, while the presence of the fat layer greatly decreased the detector sensitivity. It is also shown that probes with longer SD separations can detect light from deeper inside the medium. The simulation results are used to design a fiber optic probe which ensures that enough light is propagated inside the muscle in NIRS measurement on a leg with a fat layer of normal thickness.

[1]  Ling Lin,et al.  Influence of a fat layer on muscle oxygenation measurement using near-IR spectroscopy: quantitative analysis based on two-layered phantom experiments and Monte Carlo simulation , 2000 .

[2]  F. P. Bolin,et al.  Refractive index of some mammalian tissues using a fiber optic cladding method. , 1989, Applied optics.

[3]  T. Fukunaga,et al.  Influence of adipose tissue thickness on near infrared spectroscopic signal in the measurement of human muscle. , 1996, Journal of biomedical optics.

[4]  D T Delpy,et al.  The effect of overlying tissue on the spatial sensitivity profile of near-infrared spectroscopy. , 1995, Physics in medicine and biology.

[5]  M. Kohl,et al.  Near-infrared optical properties of ex vivo human skin and subcutaneous tissues measured using the Monte Carlo inversion technique. , 1998, Physics in medicine and biology.

[6]  Babs R. Soller,et al.  Characterization of penetration depth as a function of optical fiber separation at various absorption and scatter coefficients for a noninvasive metabolic sensor , 2004, SPIE BiOS.

[7]  S L Jacques,et al.  CONV--convolution for responses to a finite diameter photon beam incident on multi-layered tissues. , 1997, Computer methods and programs in biomedicine.

[8]  Makoto Takahashi,et al.  Accurate NIRS measurement of muscle oxygenation by correcting the influence of a subcutaneous fat layer , 1998, European Conference on Biomedical Optics.

[9]  B. Wilson,et al.  A Monte Carlo model for the absorption and flux distributions of light in tissue. , 1983, Medical physics.

[10]  Babs R. Soller,et al.  Partial Least-Squares Modeling of Near-Infrared Reflectance Data for Noninvasive in Vivo Determination of Deep-Tissue pH , 1998 .

[11]  L Wang,et al.  MCML--Monte Carlo modeling of light transport in multi-layered tissues. , 1995, Computer methods and programs in biomedicine.

[12]  S. Simsir,et al.  Noninvasive, near infrared spectroscopic-measured muscle pH and Po2 indicate tissue perfusion for cardiac surgical patients undergoing cardiopulmonary bypass* , 2003, Critical care medicine.