Photoacoustic Imaging for Cancer Diagnosis and Therapy Guidance

Photoacoustic imaging uses light as an excitation source and ultrasound imaging to detect sound waves generated by the optically-excited targets and to form images of optical absorption. With the nonionization nature of light waves and the well-established, portable, and cost-effective ultrasound imaging devices, photoacoustic imaging is capable of real-time imaging and is especially suitable for continuous and repetitive imaging of disease sites for long-term monitoring of disease progression or therapeutic outcome. This imaging technique typically offers the submillimeter imaging resolution of tissue at centimeter depths, although, by sacrificing imaging depth, the resolution could be further scaled down to the submicrometer range to reveal the organelle. Because of these advantages, photoacoustic imaging is capable of monitoring blood flow speed, detecting metabolic blood oxygen level of tumors, producing angiography of tumor vasculature networks, and tracing molecular probes to visualize the molecular pathology of cancer in vivo. Furthermore, it can also be used to noninvasively map the change of temperature distribution during thermal cancer therapy. This chapter introduces the physical mechanisms of photoacoustic signal generation in both homogenous and heterogeneous mediums, discusses the recent development of photoacoustic imaging, highlights its abilities to provide functional and molecular information about the tissue, and reviews its diagnostic use in thermal imaging. Finally, the applications of photoacoustic imaging in cancer therapies are reviewed and future outlooks for this promising translational imaging modality are considered.