Thermoacoustic and photoacoustic imaging of biological tissue with different contrasts and properties

Abstract

Microwave-induced thermoacoustic or photoacoustic imaging is a nonionizing imaging modality based on the difference in microwave or light absorption of various biological tissues. The advantage of this imaging over traditional optical imaging is that it retains intrinsic microwave or optical contrast characteristics while benefiting from the diffraction-limited high spatial resolution of ultrasound. Various tissues present particular characteristics in their absorption spectra. Photoacoustic imaging can map optical absorption distribution whereas microwave-induced thermoacoustic imaging is related to the electrical properties in the objects. Muscles which have a rich blood supply provide excellent optical contrast. In contrast high water or ion content tissues, such as muscle tissues or malignant tissues, demonstrate high contrast to fatty tissues employing microwave radiation. Besides different contrast mechanisms, microwave-induced thermoacoustic imaging may find unique applications because microwave radiation provides a deeper penetration depth in biological tissues than optical radiation. The frequency spectrum of thermoacoustic images is much lower and the spatial resolution is poorer due to the pulse width of microwave radiation. Therefore, thermoacoustic and photoacoustic imaging are associated with different characteristics based on information from tissue properties over an electromagnetic spectrum from microwave to optical bands. The reconstructed thermoacoustic and photoacoustic images with their image blending may be more accurate and comprehensive than was previously available. Also the experimental results show that breast cancer detection is a promising, and specific application field by microwave-induced thermoacoustic imaging. We are able to provide multimodality, complementary, and low cost images which can be potentially used for early cancer detection and imaging.