Principles of confocal Endomicroscopy

 Endomicroscopy is performed with a miniaturized confocal endomicroscope, where a blue laser light is used to scan the intestinal mucosa from the surface up to the deepest parts of the mucosal layer.


Confocal microscopy provides better spatial resolution than conventional fluorescence microscopy, as the images are not contaminated by light scattering from other focal planes. A low-powered laser is focused onto a single point in a defined microscopic field of view, and the same lens is used as both the condenser and objective folding optical path. The point of illumination thus coincides with the point of detection within the specimen. Light emanating from that point is focused through a pin-hole to a detector, and light emanating from outside the illuminated spot is rejected. The illumination and detection systems are in the same focal plane and are termed “confocal”. All detected signals from the illuminated spot are captured and measured. The gray-scale image created is an optical section representing one focal plane within the examined specimen. The image of a scanned region can be constructed and digitized by measuring the light returning to the detector from successive points. Single points are typically scanned in a raster pattern.


Series of confocal images within successive planes can be used to observe fine cellular or subcellular structures, and three-dimensional structures in the specimen can be imaged.

 

Schematic of confocal laser endomicroscopy

 

 A confocal laser microscope is incorporated into the distal tip of a conventional endoscope. ,  A blue laser light is emitted onto the mucosal surface and into deeper parts of the mucosal layer . The returning light is measured, and its intensity is displayed as a gray- scale image.  A single image represents an optical horizontal section of the mucosal layer.

 

The Pentax confocal endomicroscope uses a single optical-mode fiber acting as both the illumination point source and the detection pinhole, which allows confocal microscopy of the mucosal layer at high resolution (lateral resolution 0.7 µm) in addition to standard video imaging (Pentax EC-3870CIFK; Pentax, Tokyo, Japan).

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