Eric R. Weeks
Emory University, Atlanta, Georgia, U.S.A.
published in the Encyclopedia of Biomaterials and Biomedical Engineering, Taylor & Francis (2005)
Confocal microscopy is an optical imaging technique used to increase micrograph contrast and/or to reconstruct three-dimensional images by using a spatial pinhole to eliminate out-of-focus light in specimens that are thicker than the focal plane. This technique has gained popularity in the scientific and industrial communities.
The principle of confocal imaging was patented by Marvin Minsky in 1957. A confocal microscope uses point illumination and a pinhole in an optically conjugate plane in front of the detector to eliminate out-of-focus information. Only the light within the focal plane can be detected, so the image quality is much better than that of wide-field images. As only one point is illuminated at a time in confocal microscopy, 2D or 3D imaging requires scanning over a regular raster (i.e. a rectangular pattern of parallel scanning lines) in the specimen.
Three types of confocal microscopes are commercially available: confocal laser scanning microscopes , spinning-disk confocal microscopes and Programmable Array Microscopes (PAM). Confocal laser scanning microscopy yields better image quality than Nipkow and PAM, but the imaging frame rate was very slow (less than 3 frames/second) until recently; spinning-disk confocal microscopes can achieve video rate imaging—a desirable feature for dynamic observations such as live cell imaging. Confocal laser scanning microscopy has now been improved to provide better than video rate (60 frames/second) imaging by using MEMS based scanning mirrors.