Dual-axes confocal reflectance microscope for distinguishing colonic neoplasia

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Abstract
Confocal microscopes are used in bench top biological investigations to perform optical sectioning,1 and can be used for in vivo imaging if the objectives and scanning mechanisms can be made sufficiently small. Over the past decade, numerous efforts have been made to miniaturize confocal microscopes. 2, 3, 4, 5, 6, 7 In order to achieve subcellular resolution with a conventional single-axis confocal microscope, a high numerical aperture (NA) is necessary, generally utilizing complex and bulky objectives lenses for diffraction-limited focusing of beams over a wide field of view. Geometrically, a high NA correlates to a short working distance for a given aperture size, thus limiting the depth at which subsurface imaging may be performed in tissue. Due to short working distances, scanning must be performed prior to the objective, which limits the field of view and introduces optical aberrations unless compensated for by the use of multiple lenses.4 Scaling down the optics unavoidably requires a sacrifice of resolution, field of view (FOV), and/or working distance (WD). In addition, the conventional single-axis confocal design is limited in its ability to effectively reject the large amounts of scattered light generated when imaging deeply in tissues (see Section 2).8