Influence of aberrations on the image quality in optical coherence microscopy

High resolution imaging of human airways holds promise to visualize pathologic morphology and function with subcellular resolution. We have shown that endoscopic optical coherence microscopy (eOCM) is able to provide cross-sectional images with micrometer resolution. Our eOCT device is based on a supercontinuum light source, a custom made 400nm spectrometer, and a custom made 0.5 NA gradiant index (GRIN) endoscope. The endoscope is connected via a novel compact handpiece to lightsource and spectrometer.

Working at micrometer resolution, the image performance is significantly influenced by spherical and chromatic aberrations of the endoscope. In contrast to non-coherent microscopy, aberration do not just introduce blurring of the image. They rather modify the cross-section images in a complex way, improving the depth field but also introducing speckle noise and false image structures.

Here we present extensive numerical calculation of the OCM image formation, based numerical wavefront calculations and compare our results with an optical characterization of the eOCM.

We found that spherical as well as chromatic aberrations are able to provide high transvers resolution over larger field of depth compared to aberration-free imaging. Our GRIN endoscope is not corrected for spherical aberrations. This explains our astonishing good image quality over a large depth range. Our calculations also imply that Bessel or angular beam illumination, which was proposed by some groups, does degrade image quality by the intense side lobes of the point spread function.

In conclusion, our rigorous modeling of OCM imaging allows systematically improving image quality in imaging the airways and other scattering tissues.

*Presenting author