The Potential Value of Photoacoustic Imaging in the Assessment of Inflammatory Changes of Joints

This decade has witnessed a growing prevalence of chronic arthritis all around the world. Early diagnosis of arthritis can be essential for timely treatment and a better prognosis. Photoacoustic imaging (PAI), a multi-functional imaging technique, has been applied for visualizing morphological structures of peripheral joints and small vessels in small joints. Blood oxygenation and other perfusion indexes can also be calculated by PAI, allowing functional evaluation of joint tissues. The exogenous photoacoustic contrast agent that is targeted at some specific molecular biomarkers enables molecular imaging with the use of photoacoustic modalities. Several photoacoustic computed tomography (PACT) modalities have been developed for joint imaging, including some dual-modality systems, which integrate a photoacoustic system with other imaging methods. Taking advantage of the stability and maturity of commercial US units, the co-registration of photoacoustic and ultrasound (PA/US) systems with a portable probe can be an essential step for future clinical translation and promotion. This kind of dual-modal imaging system takes the advantage of compactness and high cost-efficiency of commercial ultrasound systems, and permits noninvasive real-time PA/US imaging simultaneously. The feasi- bility of this type of dual-modality PA/US system in the evaluation of joint disease has been explored and validated by recent studies. Moreover, exogenous contrast agents can facilitate molecular PAI in arthritis by binding specific molecules to those photoacoustic dyes, enabling visualizing inflammatory changes of local joints and delivering therapeutic agents for treating arthritis. Currently, researchers are making efforts to eliminate reflection artifacts, and to enhance the quality and speed of PAI acquisition for diagnosing inflammatory arthritis.