Shack-Hartmann sensor based optical quality testing of whole slide imaging systems for digital pathology

Abstract

Whole Slide Imaging (WSI) systems are used in the emerging field of digital pathology for capturing high-resolution images of tissue slides at high throughput. We present a technique to measure the optical aberrations of WSI systems using a Shack-Hartmann wavefront sensor as a function of field position. The resulting full-field aberration maps for the lowest order astigmatism and coma are analyzed using nodal aberration theory. According to this theory two coefficients describe the astigmatism and coma inherent to the optical design and another six coefficients are needed to describe the cumulative effects of all possible misalignments on astigmatism and coma. The nodal aberration theory appears to fit well to the experimental data. We have measured and analyzed the full-field aberration maps for two different objective lens-tube lens assemblies and found that only the optical design related astigmatism coefficient differed substantially between the two cases, but in agreement with expectations. We have also studied full-field aberration maps for intentional decenter and tilt and found that these affect the misalignment coefficient for constant coma (decenter) and the misalignment coefficient for linear astigmatism (tilt), while keeping all other nodal aberration theory coefficients constant.

Impact of partial coherence on the apparent optical transfer function derived from the response to amplitude edges

“…This corresponds to a difference in best focus between sagittally and tangentially oriented edges of about 1.5 µm. The overall dependence of astigmatism (and field curvature) on the field coordinate is well described by a quadratic function, in agreement with basic optical theory [3,23].…”

“…Sagittal coma is largely independent of the field position and takes a rms value equal to −5 ± 13 mλ. The dependence of these aberrations on the field coordinate is in good agreement with so-called Nodal Aberration Theory (NAT) [23], which describes the impact of misalignment on the field dependence of the primary aberrations following from basic optical theory [3].…”

Simultaneous orientation and 3D localization microscopy with a Vortex point spread function

“…We improve upon this treatment by modeling the field dependence of the aberration coefficients using the so-called Nodal Aberration Theory (NAT) instead of 2D polynomials of arbitrary order. This approach is valid for optical imaging systems with small field angles (ratio of FOV to focal length), such as telescopes or microscopes, and has been devised by Shack and Thompson (57), and later extended and used in optical design and characterization studies (58–62).…”