Introduction of an ultrathin and flexible laser scanning endoscope for color imaging and integrated PDD and future PDT

The scanning fiber endoscope (SFE), an ultrathin laser scanning endoscope capable of producing 500-line color images at 30-Hz frame rate, has been developed at the University of Washington. The SFE probe is a 1-mm diameter by 9-mm long rigid scanner at the tip of a highly flexible and robust tether (minimum bend radius < 8- mm), comprised of helically wound optical fibers and electrical wires within a protective sheath. The unique physical characteristics of this system have allowed the camera to navigate narrow passages where other technologies have suffered from reduced image quality and fragility, such as imaging the peripheral airways and bile duct. The scanning engine of the SFE allows for laser-based imaging and potential applications of pixel-accurate therapy in remote regions of the body. In this study, the standard SFE operation has been tailored to create widefield fluorescence images for photodynamic detection. A kidney with renal cell carcinoma was excised from an Eker rat after post-mortem in situ perfusion with 0.4 mM hypericin. The 442-nm blue and 532-nm green laser illumination sources were used for both standard reflectance imaging and fluorescence excitation, while the red 635- nm illumination was disabled. Red detection signal gain was increased to amplify the red fluorescence signal from the photomultiplier tube and within the computer image display. Results show green and blue reflectance images overlaid with red fluorescence signal in tumor regions of the kidney. These imaging capabilities portend future adoption of laser-based SFE imaging for real-time PDD.