Photoacoustic microscopy of arteriovenous shunts and blood diffusion in early-stage tumors

Angiogenesis in a tumor region creates arteriovenous (AV) shunts that cause an abnormal venous blood oxygen saturation (sO_2) distribution. Here, we applied optical-resolution photoacoustic microscopy to study the AV shunting in vivo. First, we built a phantom to image sO_2 distribution in a vessel containing converged flows from two upstream blood vessels with different sO_2 values. The phantom experiment showed that the blood from the two upstream vessels maintained a clear sO_2 boundary for hundreds of seconds, which is consistent with our theoretical analysis using a diffusion model. Next, we xenotransplanted O-786 tumor cells in mouse ears and observed abnormal sO_2 distribution in the downstream vein from the AV shunts in vivo. Finally, we identified the tumor location by tracing the sO_2 distribution. Our study suggests that abnormal sO_2 distribution induced by the AV shunts in the vessel network may be used as a new functional benchmark for early tumor detection.