An Experimental Phantom Study for Air-Based Quasi-Resonant Microwave Breast Imaging

The tumor detection performance of two air-based metallic microwave breast imaging systems is evaluated experimentally using breast phantoms having realistic tissue permittivities. The first system has a circular-cylindrical shape, whereas the second has a faceted hemispherical shape. No immersion medium is utilized making these systems low-loss quasi-resonant structures. The breast phantoms are composed of three distinct volumes representing structurally simplified adipose, fibroglandular, and tumor regions filled with tissue-mimicking fluids. Scattered-field data are collected, at multiple frequencies, on the inside surface of the chambers: the normal component of the electric field at 18 locations in the cylindrical chamber and 24 tangential magnetic field components in the faceted chamber. Quantitative 3-D imaging of these high-contrast phantoms is performed utilizing the finite-element contrast-source-inversion algorithm wherein an inhomogeneous numerical background, constituting prior information, is introduced. Experiments are conducted with various accuracies of this prior information, both in terms of the permittivity that is used as well as the accuracy of the geometry compared with the true regions within the phantom. Image segmentation techniques based on thresholding the 3-D reconstructed images are evaluated for tumor detection. Utilizing receiver operating characteristic (ROC) curves, it is shown that taking the intersection of multifrequency thresholded 3-D images performs the best for detecting tumors.