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.