In vivo photoacoustic imaging of swine ureters injected with methylene blue

Significance: Ureteral injuries represent a major concern during a range of surgical procedures, due to the proximity of the ureter to target surgical structures. Intraoperative identification of the ureter is critical to prevent this accidental damage. Aim: We demonstrate the first known in vivo photoacoustic imaging of the ureter in swine following intravenous administration of FDA-approved methylene blue, enabled by a software-hardware integration that has not been previously reported in the literature. Approach: Photoacoustic channel data from the ureters of two swine were acquired using a Vevo F2 ultrasound system and an Opotek Phocus Mobile laser. Images were beamformed using a delay-and-sum algorithm. Photoacoustic image quality was evaluated using contrast, signal-to-noise ratio (SNR), and generalized contrast-to-noise ratio (gCNR) metrics, measured 10 to 80 min after methylene blue injection. Results: Across the 10- to 80-min imaging window, median contrast (3.46–11.43 dB), SNR (2.84–6.99), and gCNR (0.27–0.64) confirmed sustained ureter visibility with methylene blue. Maximum image quality was observed 20- to 30-min after methylene blue injection, with significantly higher contrast, SNR, and gCNR values compared with earlier or later time points (p<0.05). Conclusions: In vivo results demonstrate that methylene-blue-enhanced photoacoustic imaging can visualize the ureter over a time duration that is consistent with the length of surgical procedures, providing initial feasibility for real-time photoacoustic-guided surgery applications.