A new technique for improving visualization of mucosal lesions during endoscopic photodynamic therapy

A new device consisting of a conventional fiberscope and a new TV system (model OTV-S5, Olympus Optical Co., Tokyo, Japan) has been developed to achieve accurate irradiation of laser light in photodynamic therapy for gastric cancer. This model has high resolution and sensitivity, and its signal can be transmitted by red, green and blue. In front of the CCD we inserted a special interference filter which has specific absorption of red light with 2.3% transmissivity at a 630 nm wavelength and a 50 nm absorption band of full width at half maximum. The average transmittance in the visible region, except for at 630 nm, was 90%. A neutral density filter with 16% transmittance was added to adjust to the sensitivity of the CCD. The device makes it possible to perform accurate irradiation, because we can observe both the lesion and the laser spot on a monitor in original colors during irradiation.