This invention relates to the detection of fluorescence and, in particular, the detection of fluorescence for cancer diagnosis.
With conventional endoscopic techniques, early cancer detection presents a diagnostic challenge even for experienced physicians. In its early stages, a cancerous tumor may only be a few cell layers thick, and thus, the surface of the tissue may not physically change sufficiently to be visible when viewed under "white light" illumination with conventional endoscopic techniques. By "white light" illumination, is meant a relatively broad range of the visible portion of the electromagnetic spectrum.
Fluorescence imaging techniques have been used to detect the presence of cancer. Fluorescence is generally defined as the emission of radiation, usually in the form of visible light, resulting from the absorption of radiation in another spectral band from a radiation source. The impetus for using fluorescence imaging in cancer detection was due in part to the recognition that normal and malignant tissue provide different fluorescence features.
One approach for using fluorescence imaging in cancer detection involves comparing the intrinsic fluorescence (also referred to as "autofluorescence" or background fluorescence that is generated by all cells due to the natural presence of fluorescent molecules inside them) of normal tissue with the intrinsic fluorescence of malignantly-transformed tissue.
Another approach for fluorescence imaging in cancer detection involves the use of exogenic substances, including fluorescent dyes, which are administered into a patient and accumulate in malignant tissue. Experiments with cultured cells indicate that the primary cause of dye accumulation in malignant tissue is due to the different metabolism rate of normal and cancerous cells. One advantage of this approach is that the fluorescence can be detected at a peak of the dye's fluorescence spectrum.