Optical and thermal properties of nasal septal cartilage

Backgrounds and Objectives: The aim of the study was to measure the spectra l dependence of optical absorption and reduced scattering coefficients and thermal conductivity and diffusivity of porcine nasal septal cartilage. Val ues of optical and thermal properties determined in this study may aid in d etermining laser dosimetry and allow selection of an optical source wavelen gth for noninvasive diagnostics for laser-assisted reshaping of cartilage. Materials and Methods: The diffuse reflectance and transmittance of ex vivo porcine nasal septal cartilage were measured in the 400- to 1,400-nm spect ral range by using a spectrophotometer. The reflectance and transmittance d ata were analyzed by using an inverse adding-doubling algorithm to obtain t he absorption (mu(a)) and reduced scattering (mu(a)') coefficients. A multi channel thermal probe controller system and infrared imaging radiometer met hods were applied to measure the thermal properties of cartilage. The multi channel thermal probe controller system was used as an invasive technique t o measure thermal conductivity and diffusivity of cartilage at three temper atures (27, 37, 50 degrees C). An infrared imaging radiometer was used as a noninvasive method to measure the thermal diffusivity of cartilage by usin g a CO2 laser source (lambda = 10.6 mu m) and an infrared focal plane array (IR-FPA) camera. Results: The optical absorption peaks at 980 nm and 1,180 nm in cartilage w ere observed and corresponded to known absorption bands of water. The deter mined reduced scattering coefficient gradually decreased at longer waveleng ths. The thermal conductivity values of cartilage measured by using an inva sive probe at 27, 37, and 50 degrees C were 4.78, 5.18, and 5.76 mW/cm degr ees C, respectively. The corresponding thermal diffusivity values were 1.28 , 1.31, and 1.40x 10(-3) cm(2)/sec. Because no statistically significant di fference in thermal diffusivity values with increasing temperature is found , the average thermal diffusivity is 1.32 x 10(-3) cm(2)/sec. The numerical estimate for thermal diffusivity obtained from infrared radiometry measure ments was 1.38 x 10(-3) cm(2)/sec. Conclusion: Values of the spectral dependence of the optical absorption and reduced scattering coefficients, and thermal conductivity and diffusivity of cartilage were measured. The invasive and noninvasive diffusivity measur ements were consistent and concluded that the infrared imaging radiometric technique has an advantage to determine thermal properties, because damage to the cartilage sample may be avoided. The measured values of absorption a nd reduced scattering coefficients can be used for predicting the optical f luence distribution in cartilage and determining optical source wavelengths for the laser-assisted cartilage reshaping studies. The thermal conductivi ty and diffusivity values can play role in understanding thermal-dependent phenomenon in cartilage during laser irradiation and determining laser dosi metry for the laser-assisted cartilage reshaping studies. Lasers Surg. Med. 27:119-128, 2000. (C) 2000 Wiley-Liss, Inc.