Abstract
Indocyanine green (ICG) is used for clinical tests, such as liver function, by means of the absorption property in near infrared light. ICG also emits near infrared fluorescence when it is excited with near infrared light. In the present study, we compared fluorescence imaging and absorption imaging of ICG using a simple imaging system composed of CCD (charge coupled device) camera and a Xenon lamp with optical filters. ICG dissolved in DMSO was injected into polyethylene tube penetrated into the head of mice at various depths. At 2 to 4mm depth from the surface of the head, the location of a piece of ICG tube was clearly detected through skin, skull bone and brain tissue by means of fluorescence imaging. In contrast, absorption imaging did not identify the shape of ICG tube nor a syringe needle at 2mm depth, indicating that the failure of identification of ICG by absorption imaging was not due to insufficiency of absorption of near infrared light. These results demonstrate that near infrared fluorescence imaging exceeds in detectability of ICG in biological tissues compared with near infrared absorption imaging. In addition, the ICG fluorescence imaging does not require intricate imaging system, such as computed tomography, when applied to detection of ICG near the surface of biological tissue.
