**5. Conclusions**

The Dartmouth microwave imaging system is quite robust because of its synergism of hardware and numerical modeling expertise. Competing implementations of microwave imaging approaches generally ignore multipath signals. In fact, most numerical models preclude their existence by not incorporating structures which would excite surface wave propagation. The Dartmouth approach directly addresses this phenomenon which has led to a range of hardware and software innovations. Most notably, by being able to pack the antennas in such a small circle about the target, various factors have aligned to make 2D imaging a reality.

*Theoretical Premises and Contemporary Optimizations of Microwave Tomography DOI: http://dx.doi.org/10.5772/intechopen.103011*

In addition, by incorporating fundamental concepts from parameter estimation theory, we have been able to implement a version of the image reconstruction process that essentially eliminates the a priori information requirement. While the log transform is most often used for purely real mathematical functions, there is precedent for its use with complex functions—notably for optical coherence tomography. The concept takes on an added level of complexity for microwave imaging because of the phase unwrapping criteria. By developing simple and effective ways to unwrap the phases, we now have an algorithm which does not require a priori information and does not converge to local minima or unwanted solutions. This type of robustness is essential when working in actual clinical situations.

Finally, the results bear out that microwave images can be diagnostically useful in the breast neoadjuvant chemotherapy monitoring setting. Initial pilot results suggest that the property changes observed as early as 30 days after treatment correlate well with final treatment response. Essentially the microwave properties provide a physiological assessment of the response which is known to occur earlier than measures based on morphological phenomena. While physiological models have been proposed that may explain the behavior observed in the imaging trials, more data is required to confirm this phenomenon. Regardless, these results suggest that microwave imaging may be a viable approach and may provide additional tools for clinicians in their fight to treat breast cancer.
