| Résumé | A number of fluorescence imaging techniques show diagnostic promise. Imaging endogenous fluorescence has been proposed as a method for cancer diagnosis. Unfortunately, tissue autofluorescence is relatively weak and poor contrast between malignant and normal tissue is seen. Contrast may be enhanced with the addition of fluorescent materials that are selectively accumulated by malignant cells, such as fluoroscein or porphyrin derivatives. The limited penetration of light at the emission maxima of these materials restricts the use of fluorescence techniques utilizing these chromophores to superficial phenomena. However, many potential applications still exist. For example, monitoring fluorescence during surgery may allow resection margins to be clearly delineated. Other exogenous chromophores that may have may have diagnostic utility include indocyanine green (ICG). Techniques based upon visualization of the distribution of ICG fluorescence (i.e. choroidal angiography) are already prominent in ophthalmology. ICG fluorescence imaging may also find a useful niche in monitoring of burns and transplant tissue. In addition, monitoring of vascular parameters during cardiac surgery presents exciting opportunities. For example, low oxygen levels (e.g. during bypass surgery) in the heart can result in alterations in microvascular permeability. As ICG is largely bound to serum albumin, it should not be seen in extravascular spaces in normal hearts. However, increased permeability will allow albumin to diffuse into the extravascular spaces, and diffuse fluorescence across the surface of the heart will be seen. In principle, the infusion of polymers (e.g. dextrans) of various molecular weights labeled with dyes that fluoresce at various wavelengths will allow the assessment of the porosity of capillary beds in such systems. Immunofluorescence techniques have the potential to provide unmatched sensitivity and specificity. The unique nature of antibody–antigen interactions ensures specific delivery of the fluorophore to the site of interest. The specific interaction of labeled antibodies with antigens means that the fluorophore persists in the body for a prolonged period of time (days). Following a single injection of labeled antibody, repeated measurements on the same site over the course of hours or days allow kinetic information to be readily obtained. In principle, this means that the effect of therapeutic intervention, i.e. radiation therapy, chemotherapy, etc., can be monitored. |
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