Sensitivity and Identifiability of Tumor-Related Changes in Longitudinal Microwave Breast Imaging
Microwave imaging could monitor breast tumor response to neoadjuvant chemotherapy, but between-visit changes in breast positioning and normal tissue may confound tumor-related changes. We use eight patient-specific dielectric models from longitudinal MRI of two patients at four time points. For each model, 24-port S-parameters were simulated from 1 to 3 GHz, and Jacobians computed for tumor permittivity and loss, fibroglandular tissue (FGT) permittivity, and breast rotation and translation. 1 mm positioning changes produced changes 20 to 50 times larger than a 10% tumor permittivity change above 2 GHz. Nevertheless, tumor sensitivity patterns were weakly aligned with positioning patterns, tumor-FGT similarity exceeded 0.8 at only some visits, and the Jacobians remained well conditioned. Tumor responses are thus small but separable; monitoring will require positioning correction, frequency selection, and noise-aware detectability analysis.