Articular Cartilage Optical Properties in the Spectral Range 300–850 nm

Abstract

Measurements of absolute total reflectance were recorded from weight-bearing (n = 9) and nonweight-bearing (n = 9) equine articular cartilage specimens from 300 to 850 nm using a spectrophotometer with integrating sphere attachment. Following correction of measured spectra for interfacial reflections and edge losses, Kubelka-Munk theory was applied to estimate absorption and scattering coefficient, one-dimensional light intensity distribution, and light penetration depth. Kubelka-Munk absorption coefficients ranged from ∼7 cm-1 at 330 nm to ∼1 cm-1 at 850 nm. A localized absorption peak was noted at ∼340 nm. Above 510 nm, weight-bearing cartilage demonstrated significantly higher absorption coefficients than nonweight-bearing tissue (paired t-test, p<0.05). Kubelka-Munk scattering coefficients ranged from ∼40 cm-1 at 360 nm to ∼6 cm-1 at 850 nm. No statistical differences in scattering coefficient were noted between weight-bearing and nonweight-bearing tissue. Penetration depths predicted by Kubelka-Munk theory ranged from 0.6 mm at 350 nm to over 3 mm at 850 nm. Stronger absorption in weight-bearing cartilage compared to nonweight-bearing tissue resulted in lower light penetration depths in weight-bearing cartilage at all wavelengths longer than 510 nm. © 1998 Society of Photo-Optical Instrumentation Engineers.