Ultrasound and microwave scanners are developed to scan the breast on the presence of cancer. Typically, these modalities are used independently. Here we investigate if we can achieve an improved resolution if we merge both modalities into a single device. In particular, we test if we can improve the resolution of the resulting images by employing a joint inversion method on both data sets as compared to doing two independent inversions leading to two independent images. For the joint inversion an error functional is employed that contains two terms; the first one represents the mismatch between the measured and modeled acoustic and electromagnetic wave fields whereas the second term links the two reconstructed contrast profiles with each other. Results show that joint Born inversion leads indeed to an improved reconstruction as compared to two independent Born inversions.

We present a novel microwave imaging technique for sparse domain imaging applications. In the proposed method, inverse scattering algorithm modified gradient method (MGM) is combined with a fast iterative shrinkage-thresholding algorithm to improve the resolution and robustness of the MGM by enforcing the sparsity in the imaging domain. The numerical experiments show that the proposed method achieves higher resolution and robustness compared with that of classical MGM. For nonsparse domain reconstruction, the wavelet transformation is adopted to convert nonsparse spatial domain into a sparse wavelet coefficient domain. The feasibility of the proposed method in the wavelet domain is demonstrated through the numerical experiments.