Methods for the endoscopic photographic and visual detection of helium cadmium laser‐Induced fluorescence of photofrin II

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Abstract
Endoscopic detection of small tumors is key to the early diagnosis and treatment of malignancy. This paper describes a simple, endoscopic detection system which enables tumor localization and a permanent record based on the laser–induced fluorescence of dihematoporphyrin ether (LIFD). Spectral analysis of dihe‐matoporphyrin ether (DHE, Photofrin II) was performed with a Perkin Elmer LS‐5 scanning fluorimeter. DHE at concentrations of 50 μg/ml and 5 μg/ml in 95% ethanol were tested, demonstrating fluorescence quenching at 50 μg/ml DHE at 406 nm excitation. This phenomenon was not observed at 442 nm excitation. Based on this data and the availability of the helium cadmium laser, a series of endoscopic detection systems was developed and tested utilizing a LiConix 4240NB helium cadmium laser (TEMoo, 442 nm, 40 mW). A fiber with a microdiverging (MDL) lens was used. Irradiance achieved at the tip of the fiber was 31.58 mW/cm2 for MDL. A Corning 34832 (550 nm) sharp cutoff barrier filter was coupled to an Olympus OES BF2T10 bronchoscope. Successful detection of LIFD was obtained.Direct observation of LIFD is possible when wearing Laserguard argon safety goggles (OD 15 at 488 nm, OD 11 at 514 nm). Photographic recording of LIFD was performed with the following cameras and parameters: Olympus OM‐2S camera (OM2) with EES135 film (ISO 1600) with a 4‐second exposure (method 1) and the Olympus OES SCP‐10 instant camera with Polaroid 779 (ISO 640) film and a 120‐second exposure (method 2). The photographic methods demonstrate the red fluorescence of DHE on filter paper disks at concentrations of 0.5 μg/ml (500 ng/ml). The visual method allows detection of as little as 0.25 μg/ml (250 ng/ml) DHE. These methods provide a low‐cost method for tumor detection within the range of DHE concentrations employed clinically. The use of the helium cadmium laser for laser‐induced fluorescent endoscopic detection of Photofrin II is reported.