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Modulated luminescence (LUM) technique was applied to analyze photophysical processes in the cortical layer of
human skull bones. The theoretical interpretation of the results was based on the optical excitation and decay rate
equations of the fluorophore and on the molecular interaction parameter with the photon field density in the matrix of the
bone. Using comparisons of the theory with the frequency response of dental LUM it was concluded that the optically
active molecular species (fluorophore) in the bones is hydroxyapatite. An effective relaxation lifetime of skull cortical
bone was derived theoretically and was found to depend on the intrinsic fluorophore decay lifetime, on the photon field
density, and on the thickness of the bone. The experimentally measured dependencies were in excellent agreement with
the theoretical model. The theory was able to yield measurements of the optical scattering coefficient, optical absorption
coefficient, and mean coupling coefficient. These results show that the quantitative LUM can be used as a sensitive
method to measure optical properties of the active fluorophore in cortical skull bones and the optical-field-induced
molecular interaction parameter. When calibrated vs. laser intensity, the modulated luminescence can also be used to
measure human skull thickness. These traits can be applied to monitor the bone mineral density (BMD) and, ultimately
can be used as potential markers of bone health or disease, such as osteoporosis or bone cancer.
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