Microwave-Induced Thermoacoustic Imaging of Small Animals Applying Scanning Orthogonal Polarization Excitation

The traditional microwave-induced thermoacoustic imaging (MITAI) technique usually suffers from the problem of inhomogeneous microwave power distribution in the sample under test, which in turn renders the loss of some features of the sample in the image. To address this problem, circularly polarized antennas (CPA) have been used in MITAI to improve the image quality. However, the advantage of CPA in homogenizing the field distribution has been only validated using small samples with very simple structures. For complicated biological samples like small animals or human breasts featured with highly inhomogeneous tissue distributions, the performance of CPA-based MITAI is significantly worse than expected. Moreover, the applied CPAs generally have low efficiency, limited power capacity and narrow bandwidth. Thus, a more feasible and efficient method for homogenizing the power distribution is demanded. This work proposes a novel MITAI modality to homogenize the microwave power deposition in the sample and improve the image quality for small animal imaging via scanning orthogonal polarization (SOP) excitation, which uses a linearly polarized antenna. Two small animal samples, a small mouse and a frog, are experimentally investigated by the MITAI-SOP method. The results indicate that the SOP excitation mechanism can completely reveal the structure of the small animals due to improved power homogeneity and the proposed technique is superior to circularly polarized antenna (CPA) based modality since the former avoids the deficiency of CPA in bandwidth, power capacity and efficiency. This work presents a practical and easy-to-implement paradigm for high-quality imaging of small animals and big biological samples using MITAI.