PDT用内視鏡装置の開発、第三報

Abstract

In bronchial, esophageal and gastric photodynamic therapy (PDT) we were dazzled by the reflection of red laser light during photoradiation, especially in the use of the pulse laser such as an excimer dye laser. Initially we placed a green filter on the eyepiece of the fiberscope to protect the naked eye from being dazzled during photoradiation. Later, we also inserted a green filter in front of the CCD-camera in an OES-TV system with a NTSC signal. The red spot of laser light could be observed clearly, but the mucosal image turned to green and the boundary between cancer and surrounding mucosa became unclear. We, therefore, developed a new device for endoscopic photoradiation that consists of a conventional fiberscope and a new OES-TV system which has a high resolution and sensitivity with automatic gain controller and the signal can be sent out by RGB. We inserted an interference filter specially made to order in front of the CCD which specifically absorbs a red light, whose transmissivity rate at 630 nm wavelength is 15% and the full width at half maximum is 26 nm, while an average transmissivity is 94%. In order to make an optimal balance between a white xenon light and the red laser beam, we also inserted a neutral density filter of ND-0.8 which transmits 16%. However, these filters were not enough to absorb the red laser beam. By this trial we could find the spectral specificity of the filter to make the optimal balance in the use of the excimer dye laser of 4mJ/pulse and 80Hz. In conclusion, the filter should be qualified the specifications as follows: an average transmittance requires more than 20%, the transmissivity rate at 630 nm should be less than 1%, and the rates between an average transmittance and the transmissivity rate at 630 nm should be more than 20 times.