Photodynamic diagnosis system using green light excitation for the extension of diagnostic depth for gastric and bladder cancers

In the endoscopic diagnosis of gastric and bladder cancers, the diagnostic accuracy depends on doctors’ skill and experience, occasionally leading to misdiagnosis of cancers. To overcome this challenge, photodynamic diagnosis with 5-aminolevulinic acid (ALA-PDD) induced protoporphyrin IX (PpIX) is receiving increasing attention and has been proven to be effective and safe for cancer diagnosis. ALA-PDD can detect cancer cells by the red fluorescence emitted from PpIX excited using a blue-violet light at a wavelength of 405 nm. However, the diagnostic depth is limited owing to the high absorption and scattering nature of the tissues around a 405-nm wavelength, making it ineffective for intramucosal diagnosis. We are developing a PDD diagnostic system using a green light at a wavelength of 505 nm, which is less likely to be attenuated by absorption of mucosa tissue, to improve the detectable depth of PpIX accumulated in gastric and bladder cancers. Since such excitation wavelength can reach deeper tissues, we expect that our system will expand the diagnostic area for gastric and bladder cancer.

Daisuke Ihara, Hisanao Hazama, Takahiro Nishimura, Yoshinori Morita, Kunio Awazu: "Fluorescence detection of deep intramucosal cancer excited by green light for photodynamic diagnosis using protoporphyrin IX induced by 5-aminolevulinic acid: an ex vivo study," Journal of Biomedical Optics 25(6):063809 (2020). 

Hiroki Takishima, Daisuke Ihara, Takahiro Nishimura, Hisanao Hazama, Kunio Awazu: "Investigation of the Exciation Wavelength for Extension of Diagnostic Depth in 5-aminolevulinic Acid-based Photodynamic Diagnosis of Bladder Cancer," Journal of Japan Society for Laser Surgery and Medicine 41(4):297-306 (2021). [in Japanese]