In vivo measurements of the wavelength dependence of tissue-scattering coefficients between 760 and 900 nm measured with time-resolved spectroscopy

We present in vivo values for the optical transport coefficients (μ_a, μ_s′) of the adult human forearm, calf, and head from 760 to 900 nm measured with time-resolved spectroscopy. The accuracy of the method is tested with tissue-simulating phantoms. We obtain μ_s′(λ) ≈ 1.1 - (5.1 × 10^-4 λ) mm^-1 (forearm), 1.6 - (8.9 × 10^-4 λ) mm^-1 (calf), and 1.45 - (6.5 × 10^-4 λ) mm^-1 (head), where λ is measured in nanometers. At 800 nm we obtain μ_a = 0.023 ± 0.004 mm^-1 (forearm), 0.017 ± 0.005 mm^-1 (calf), and 0.016 ± 0.001 mm^-1 (head). Our values differ substantially from published in vitro data. In particular, our transport coefficients for the adult head are substantially lower than previously reported values for adult human cerebral matter and pig skull cortical bone measured in vitro.