Temperature reconstruction by estimating the thermophysical and optical properties of tissue during interstitial laser heating

A theoretical study was undertaken to evaluate the potential of multiple-parameter dynamic temperature reconstruction during interstitial laser heating. An iterative parameter estimation algorithm is used to reconstruct temperatures, based on Newton-Raphson inversion with Levenberg-Marquardt regularization to compensate for ill-conditioning. The algorithm minimizes errors between model-predicted and measured temperatures at sensor locations to obtain estimates of the effective thermal conductivity, volumetric heat capacity, optical absorption and reduced scattering coefficients. It has been shown that reconstruction accuracy depends on the number, location and spacing of sensors. Noise degrades reconstruction accuracy but only between the source and the first sensor located at relevant array-source distances of 3-5 mm. Parameter estimates confirm inherent ill-conditioning of the problem and indicate limited success of regularization. Results suggest that the potential for accurate temperature reconstruction is limited principally by the accuracy of source/sensor placement and by reduced parameter sensitivities at practical sensor locations.