Endoscopic frequency-domain fluorescence lifetime imaging for clinical cancer photodetection: apparatus design

We describe a new fluorescence imaging device for clinical cancer photodetection in hollow organs in which the image contrast is derived from the fluorescence lifetime of the fluorochrome at each point in a 2D image. Lifetime images are created from a series of images obtained from two gain-modulated image intensifiers. One of them (II-1) detects the light-induced tissue fluorescence, whereas the other (II-2) detects the backscattered fluorescence excitation light. This light is modulated at the same frequency as the detectors, resulting in homodyne phase-sensitive image. These stationary phase-sensitive images are collected using two CCD cameras, digitized and manipulated with a mathematical operator in real time. A series of such images, obtained with both image intensifiers at various phase shifts between their gain modulation and the modulation of the excitation light, is used to determine phase angle and/or the modulation of the fluorescence emission at each pixel. The reference values of these phase angles and modulations are obtained with II-2, whereas II-1 enables the measurement of the phase and modulation of the fluorescence. Phase and modulation are related to the fluorescence lifetime of the fluorochrome. An advantage of the experimental method proposed here is that pixel-to-pixel scanning is not required to obtain the fluorescence lifetime image, as the information from all pixels is obtained at the same time.