Optical Coherence Microscopy Endoscope

Optical Coherence Microscopy (OCM) is a combination of an OCT system and a confocal microscope. It has a coherence gate to provide high axial resolution and high numerical aperture optics coupled to a fiber pinhole to provide high lateral resolution. As currently implemented, OCM is a large table top instrument, and not suited to in vivo imaging. Our goal is to develop a handheld rigid endoscope with a 5 mm diameter tip, 1 mm scan width, and 2 µm lateral resolution. This probe will replace the current sample arm optics and should allow non-invasive cellular imaging.

The endoscope optical design consists of an afocal Hopkins relay lens system and a 0.4 NA objective (Figure 1). X-Y scanning is performed distally with micro galvo scanners incorporated into the endoscope. 2 doublets will serve as scanning lenses and relay the stop from the galvos to the afocal relay stop. To allow focusing at various depth in the tissue, the endoscope housing is designed in two pieces screwed together with a fine pitch threads near the location of the afocal relay. The outer housing holds the distal window, and the inner housing holds the refractive optics. A small rotation of the outer housing moves the lenses proximal and distal relative to the window, causing the focal location in the tissue to change. Another complicating factor with most OCM systems is that the pathlength in the reference arm must be adjusted to account for a change in pathlength in the reference arm during focusing. The sample arm pathlength changes because light in the sample arm is travels through less air and more tissue as the focus is moved deeper. We will avoid this problem in our endoscope design by filling the space between the final objective lens and the window with distilled water. Since the refractive index of tissue is close to water, and the focus will be adjusted by less than 1 mm, misalignment of the focus and coherence gate in tissue will be negligible. The housing will be designed to accommodate the displacement of water during focusing.

Figure 1- Endoscope design

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