The Foster Research Group
Tissue Spectroscopy
Representative publications
J.C. Finlay and T.H. Foster. Effect of pigment packaging on diffuse reflectance spectroscopy of samples containing red blood cells. Opt. Lett. 29, 965-967 (2004).
J.C. Finlay and T.H. Foster. Hemoglobin oxygen saturations in phantoms and in vivo from measurements of steady state diffuse reflectance at a single, short source-detector separation. Med. Phys. 31, 1949-1959 (2004).
J.C. Finlay and T.H. Foster. Recovery of hemoglobin oxygen saturation and intrinsic fluorescence using a forward adjoint model. Appl. Optics 44, 1917-1933 (2005).
W.J. Cottrell, A.R. Oseroff, andT.H. Foster. A portable instrument that integrates irradiation with fluorescence and reflectance spectroscopies during clinical photodynamic therapy of cutaneous disease. Rev. Sci. Instrum. 77, 064302 (2006).
Reflectance Spectroscopy in Tissue
Reflectance spectroscopy reports the absorption and scattering properties of tissue. Various strategies for separating the contributions of absorption and scattering in attenuation measurements have been proposed and evaluated. We have adopted broad band steady state methods that are based on either diffusion or P3 approximations to radiative transfer. Because of our interest in cancer and in photodynamic therapy in particular, we have been especially interested in monitoring hemoglobin oxygen saturation using reflectance techniques.
We have published on experimental methods for measuring spatially-resolved diffuse reflectance spectra and on characterizing laboratory phantoms that mimic optical properties of tissue. In M.G. Nichols et al. (1997) we described our first reflectance system and experimental results in model systems, which were based on a diffusion theory approximation method. These ideas were extended to a more realistic tissue-simulating phantom using intact red blood cells (Hull et al., Phys. Med. Biol. 1998), to phantoms containing red blood cells and mitochondria (Hull and Foster, Appl. Spectrosc. 2001), and to a rodent tumor model in vivo, where the effects of carbogen breathing on hemoglobin oxygen saturation were studied (Hull et al., Brit. J. Cancer 1999). An evaluation of the relationship between macroscopic, volume-averaged estimates of hemoglobin oxygen saturation reported by near infrared spectroscopy and microscopic heterogeneities in saturation assessed by cryospectroscopy was reported in D.L. Conover et al. (2000). During his thesis research, Ed Hull developed a method based on a higher order, P3 approximation to radiative transfer that recovers accurate absorption and scattering spectra in more highly absorbing media and at shorter source-detector separations (Hull and Foster, JOSA A 2001). The P3 approximation was applied in red blood cell phantoms and in a rodent tumor model in vivo by Jarod Finlay, who used it to develop a reflectance method based on a single, short source-detector separation. This enabled the use of probes much smaller than those typically used with techniques based on the diffusion theory approximation (Finlay and Foster, Med. Phys. 2004). Finlay and Foster (Opt. Lett. 2004) also described an important “pigment packaging” correction to reflectance spectra acquired at wavelengths corresponding to the Soret band of hemoglobin.