A preclinical prototype of a transcutaneous thermal therapy system has been developed for the targeted treatment of breast cancer cells using focused microwaves as an adjuvant to radiation, chemotherapy, and high intensity focused ultrasound (HIFU). The prototype system employs a 2D array of tapered microstrip patch antennas operating at 915 MHz to focus continuous-wave microwave energy transcutaneously into the pendent breast suspended in a coupling medium. Prior imaging studies are used to ascertain the material properties of the breast tissue, and this data is incorporated into a multiphysics model. Time-reversal techniques are employed to find a solution (relative amplitudes and phase) for focusing at a given location. Modeling tests of this time-reversal focusing method have been performed which demonstrate good targeting accuracy within heterogeneous breast tissue. Experimental results using the laboratory prototype to perform focused heating in tissue-mimicking gelatin phantoms have demonstrated 1.5 cm diameter focal spot sizes and differential heating at the desired focus sufficient to achieve an antitumor effect confined to the target region.
A microwave imaging system for real-time 3D imaging of differential temperature has been developed for the monitoring and feedback of thermal therapy systems. Design parameters are constrained by features of a prototype focused microwave thermal therapy system for the breast, operating at 915 MHz. Real-time imaging is accomplished with a precomputed linear inverse scattering solution combined with continuous Vector Network Analyzer (VNA) measurements of a 36-antenna, HFSS modeled, cylindrical cavity. Volumetric images of differential change of dielectric constant due to temperature are formed with a refresh rate as fast as 1 frame per second and 1°C resolution. Procedures for data segmentation and post-processed S-parameter error-correction are developed. Antenna pair VNA calibration is accelerated by using the cavity as the unknown thru standard. The device is tested on water targets and a simple breast phantom. Differentially heated targets are successfully imaged in cluttered environments. The rate of change of scattering contrast magnitude correlates 1:1 with target temperature.
We evaluate several high‐order quadrature schemes for accuracy and efficacy in obtaining orientation‐averaged single‐scattering properties (SSPs). We use the highly efficient MIDAS to perform electromagnetic scattering calculations to evaluate the gain in efficiency from these schemes. MIDAS is shown to be superior to DDSCAT, a popular discrete dipole approximation (DDA) method. This study is motivated by the fact that quality physical precipitation retrievals rely on using accurate orientation‐averaged SSPs derived from realistic hydrometeors as input to radiative transfer models (RTM). The DDA has been a popular choice for single‐scattering calculations, due to its versatility with respect to target geometry. However, being iterative‐solver‐based (ISB), the most used DDA codes, for example, DDSCAT and ADDA (formerly, Amsterdam DDA), must solve the scattering problem for each orientation of the target separately. As the size parameter and geometric anisotropy of the hydrometeor increase, the number of orientations needed to obtain accurate orientation‐averages can increase drastically and so does the computation cost incurred by the ISB‐DDA methods. MIDAS is a Direct‐Solver‐Based (DSB) code, its decomposition of the original large matrix with a high rank into multiple more manageable smaller matrices of lower ranks makes it much more computationally efficient while maintaining excellent accuracy. In addition, direct solvers consider all requested orientations at once, giving MIDAS further advantage over popular ISB‐DDA methods. MIDAS, when combined with high‐order quadrature for orientation averaging, can be greater than three orders of magnitude more efficient in obtaining RTM‐ready SSPs of complex‐shaped hydrometeors than existing ISB‐DDA methods, with the native quadrature schemes they offer.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.