Objective tumor distinction in 5-aminolevulinic acid-based endoscopic photodynamic diagnosis, using a spectrometer with a liquid crystal tunable filter.

Background: Recent improvement of the endoscopic system such as image enhancement has led to the better accuracy of the diagnosis of the gastric cancer. However, the objective and efficient detection method of the gastric cancer is still needed because the detection efficiency could sometimes be low due to the fact that the image enhancement diagnosis needs magnification for its full utilization. The photodynamic diagnosis (PDD) with oral intake of 5-aminolevulinic acid (5-ALA) has been widely used for the detection of the cancerous region for bladder cancer and glioblastoma. The application of the 5-ALA based PDD (5-ALA PDD) to the diagnosis of gastric cancer is recently reported. The efficiency of the detection is reported to be good, however, the objectivity of the method can be impaired by the photobleaching effect with fast decreasing of the intensity of the fluorescence under light exposure. In this article, we investigated the fluorescence spectrum of the gastric tumor and non-tumor mucosa of 5-ALA PDD and revealed the property of the photobleaching effect.

Methods: Example cases of PDD endoscopy of gastric tumor were investigated for cases of endoscopic submucosal dissection (ESD). Newly developed spectrometer using a spectrometer with a liquid crystal tunable filter was used for investigating the fluorescence spectrum of 5-ALA PDD. The assumed tumor region and non-tumor region in gastric mucosa were biopsied and the fluorescence spectrum was measured using the spectrometer consecutively several times, to estimate the photobleaching effect.

Results: The fluorescence spectrum has a primary peak at 630 nm, with a broad peak ranging from 660 to 700 nm. The 630 nm peak diminished quickly upon ultraviolet light exposure, whereas the broad peak from 660 to 700 nm diminished slowly. The sum of the altitudes at 660-700 nm, normalized to the altitude at 600 nm, was not as affected by the photobleaching effect as the 630 nm peak was, and can thus be used for 5-ALA-based PDD.

Conclusions: The 5-ALA PDD using the average fluorescence altitude of 660-700 nm instead of the peak altitude at 630 nm, is shown to be more effective in distinguishing between tumorous and non-tumorous tissues, because of the lower photobleaching effect at this specific spectral range. The finding is expected to greatly improve the objective diagnosis of gastrointestinal cancers by 5-ALA-based photodynamic diagnostic endoscopy.