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. 2015 Jun:42:38-43.
doi: 10.1016/j.compmedimag.2014.11.005. Epub 2014 Nov 18.

Digital pathology with Fourier ptychography

Roarke Horstmeyer  1 , Xiaoze Ou  2 , Guoan Zheng  3 , Phil Willems  4 , Changhuei Yang  2
Affiliations

Digital pathology with Fourier ptychography

Roarke Horstmeyer et al. Comput Med Imaging Graph. 2015 Jun.

Abstract

Fourier ptychographic microscopy (FPM) is a recently introduced method of acquiring high-resolution, wide field of view (FOV) giga-pixel histology images. The FPM procedure first acquires a sequence of low-resolution images of a sample under variable-angle illumination. It then combines these images using a novel phase retrieval algorithm to improve the employed microscope's resolution beyond its conventional limit. Here, we first describe how FPM's resolution improvement can enhance wide FOV histology imaging. Second, we show that FPM also records a thin sample's optical phase, which can help pathologists digitally extract as much information as possible from a given histology slide.

Keywords: Computational imaging; Digital pathology; Microscopy; Structured illumination; Super-resolution.

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Figures

Fig. 1
Fig. 1
The FPM setup. (a) LED array sequentially illuminates a sample from different directions, which is then imaged by a 2X microscope objective (MO) lens. (b) Actual FPM setup, showing the LED array and an inset of a single color LED. (c) Single image of resolution target with this 2X objective offers a wide FOV, but cannot resolve group 8 (~6 μm resolution). (d) FPM-reconstructed image resolves group 9 (~0.75 μm resolution).
Fig. 2
Fig. 2
Example grayscale FPM image of a small central area (0.6mm2) of histology slide. (a) Single image viewed in detail (bottom inset) exhibits a low resolution. (b) FPM recovers enhances resolution, and reconstructs the phase of the optical field exiting the sample as shown in (c).
Fig. 3
Fig. 3
FPM enables digital refocusing. (Top) AF resolution target axially offset from the microscope’s focal plane captures raw images that exhibit defocus artifacts with respect to an in-focus raw image, shown in center. (Bottom) FPM reconstructions of the AF resolution target using 137 raw images exhibits resolution improvement, even though the original raw images are significantly defocused. For recovery at z=+/− 150 μm, we used digital propagation to refocus the complex recovered image by these a-priori known sample defocus distances, as detailed in [8].
Fig. 4
Fig. 4
(a) FPM phase map of microspheres, allowing us to verify the accuracy of our tissue scattering parameter estimation procedure. (b) Cropped regions of the phase image around two different-sized microspheres. (c) Gradient of the phase in (b). Variances from the regions in (b) and (c) are used to determine the microsphere’s scattering and reduced scattering coefficients following Eq. (1) and Eq. (2), respectively.
Fig. 5
Fig. 5
(a) full color FPM gigapixel image of a histology slide (120 mm2 FOV). (b) Recovered phase from a 0.2 mm2 region at the sample’s center. (c) Scattering coefficient μs for this area of tissue, computed using Eq. (1). (d) Reduced scattering coefficient μs′ for the same area of tissue from Eq. (2), here shown on log scale. False color scales are noted below each image.
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