Holographic Histopathology Enables Fast, Precise Diagnostics

Because most microscopic specimens are translucent to visible light, conventional histological methods achieve image contrast using exogenous labels.

Optical diffraction tomography is a microscopy technique for reconstructing the refractive index of a tissue sample from its scattered field images obtained with various illumination angles. It enables label-free high contrast visualization of transparent samples. The complex scattered field transmitted through the sample is first retrieved using off-axis holography, then the scattered fields obtained with various angle of illuminations are mapped in the Fourier space enabling the reconstruction of the sample refractive index.

Bioscientists at the Korea Advanced Institute of Science and Technology (Daejeon, Republic of Korea) and their colleagues developed label-free volumetric imaging of thick-tissue slides, exploiting refractive index distributions as intrinsic imaging contrast. The present method systematically exploited label-free quantitative phase imaging techniques, volumetric reconstruction of intrinsic refractive index distributions in tissues, and numerical algorithms for the seamless stitching of multiple three-dimensional tomograms and for reducing scattering-induced image distortion.

The scientists demonstrated label-free volumetric imaging of thick tissues with the field of view of 2  mm  ×  1.75  mm  ×  0.2  mm with a spatial resolution of 170  nm  ×  170  nm  ×  1,400  nm. The number of optical modes, calculated as the reconstructed volume divided by the size of the point spread function, was ∼20  giga voxels. They have also demonstrated that different tumor types and a variety of precursor lesions and pathologies can be visualized with the present method.

The team demonstrated the capacity of their novel method by imaging a variety of different cancer pathologies: pancreatic neuroendocrine tumor, intraepithelial neoplasia, and intraductal papillary neoplasm of bile duct. They imaged millimeter-scale, unstained, 100-μm-thick tissues at a subcellular 3D resolution, which enabled the visualization of individual cells and multicellular tissue architectures, comparable to images obtained with traditional chemically processed tissues.

YongKuen Park, PhD, a professor and senior author of the study, said, “The images obtained with the proposed method enabled clear visualization of different morphological features in the various tissues allowing for recognition and diagnosis of precursor lesions and pathologies. We expect optical diffraction tomography to provide faster and more precise diagnostics in histopathology and intraoperative pathology consultations.” The study was published on April 29, 2021 in the journal Advanced Photonics.

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Korea Advanced Institute of Science and Technology