Contrast agents

Fluorescence confocal imaging is only possible using exogenous fluorescence contrast agents. Potentially suitable agents are fluorescein, acriflavine, or cresyl violet. The most common contrast agents are acriflavine hydrochloride (0.05% in saline; topical use only) or fluorescein sodium (5-10 ml of a 10% solution; intravenous application).

 

Confocal imaging following staining with acriflavine hydrochloride and fluorescein sodium reveals a characteristic morphology of mucosal tissue. Whereas topically used acriflavine hydrochloride strongly labels the superficial epithelial cells including nuclei, intravenously applied fluorescein sodium distributes throughout the entire mucosa with a strong contrast within the connective tissue and the capillary network. Fluorescein binds to serum albumin and remaining, unbound dye molecules pass across systemic capillaries and enter the tissue highlighting the extracellular matrix. Confocal images can be generated simultaneously with endoscopic images and allows identification of typical histologic structures within the upper and lower GI-tract. Fluorescence confocal imaging is only possible using exogenous fluorescence contrast agents. Potentially suitable agents are fluorescein, acriflavine, or cresyl violet.

 

 

	The orientation of images and contrast agents used for endomicroscopy. Conventional histology allows differentiation of the mucosal and submucosal layers on a vertical axis, whereas endomicroscopy provides images in a horizontal axis. The depth of infiltration therefore has to be assessed using a series of images.
	Most commonly, endomicroscopy is carried out after intravenous administration of fluorescein. Colonic crypts, goblet cells, and connective tissue are readily visible at high resolution. However, due to the pharmacokinetic properties of fluorescein, nuclei are not visible in all horizontal sections. Acriflavine can be used as a topical dye, which highlights especially nuclei and cell membranes.