Real-Time 3D Microwave Monitoring of Interstitial Thermal Therapy

We report a method for real-time 3D monitoring of thermal therapy through the use of non-contact microwave imaging. This method is predicated on using microwaves to image changes in the dielectric properties of tissue with changing temperature. Instead of the precomputed linear Born approximation that was used in prior work to speed up the frameto- frame inversions, here we use the nonlinear Distorted Born Iterative Method (DBIM) to solve the electric volume integral equation to image the temperature change. This is made possible by using a recently developed GPU accelerated conformal finite difference time domain (CFDTD) method to solve the forward problem and update the electric field in the monitored region in each DBIM iteration. Compared to our previous work, this approach provides a far superior approximation of the electric field within the volume integral equation (VIE), and thus yields a more accurate reconstruction of tissue temperature change. The proposed method is validated using a realistic numerical model of interstitial thermal therapy for a deep seated brain lesion. With the new DBIM, we reduced the average estimation error of the mean temperature within the region of interest from 2.5 to 1.0 degrees for the noise-free case, and from 2.9 to 1.7 degrees for the 2% background noise case.