A temperature study of laser-irradiated bone

A method for predicting the temperature of laser-irradiated bone has been developed. The method uses a numerical model to predict temperature in a bone sample irradiated with a particular wavelength of light. The model was based on the heat conduction equation with the laser radiation accounted for by a volumetric heat generation term based on the absorption coefficient at the wavelength being used and Beer's Law of exponential absorption. Two beam profiles, top hat and Gaussian, were used to model the incident beam, so the effect of beam profile on temperature distribution could be examined. Experimental runs were performed by irradiating samples of bone with two different laser wavelengths and measuring the temperature of the bone at four locations. A CO₂ laser at 10.6 µm and a Nd: YAG laser at 1.06 µm were used at powers from 5 to 40 Watts using approximately a 10 mm diameter beam. Additional experiments were performed to ascertain the accuracy of reported values for the absorption of 1.06 µm wavelength light by bone. The results of the experiments led to a value for the absorption coefficient for bone at 1.06 µm wavelength of 279/m and a reflectivity of 0.18. Using this value for the absorption coefficient, the model results were reconciled to the YAG experimental data. Charts plotting temperature against time for several locations have been generated and included as a reference for further research. Possibilities for laser-bone applications include cutting, drilling, bone shaping, thermal therapy, welding, and diagnostics and this research may enhance the development of such applications.