Recently, a research team led by Associate Prof. PAN An from Xi’an Institute of Optics and Precision Mechanics (XIOPM) of the Chinese Academy of Sciences (CAS) reported a feature domain-based FPM (termed FD-FPM) computational framework to realize non-blocked full-FOV reconstruction.
The study was published in Optica, and selected as the cover story.
Pathological analysis has been the gold standard of disease detection especially tumor diagnosis. Conventional digital pathology relies on high-precision movement of a high numerical aperture (NA) objective to obtain the entire field of view (FOV) for a tissue slide, whose high cost severely hinder its widespread applications. Fourier ptychographic microscopy (FPM) digitalizes high-resolution images with large FOV without mechanical scanning, but suffers from vignetting artifacts, and becomes particularly susceptible to systematic errors. Over a decade, therefore, the application of FPM in digital pathology is only limited to scientific research, and has not been widely accepted and recognized.
In this study, researchers theoretically pointed out that the fundamental reason for vignetting artifacts and sensitivity to systematic errors is the mismatch between forward model predictions and practical measurements. Different from traditional methods focusing on image itself, the reported FD-FPM switches to optimizing the feature of images. During the iterations, the updated target is transformed from the traditional complex amplitude to the complex gradient of images.
Such design plays an essential role in bridging the gap between theoretical model and experimental data. Intensive simulations and experiments have been conducted and verified that, FD-FPM enables elimination of vignetting artifacts at the edge of images without block operation, and exhibits impressive robustness to various systematic errors (positional shifting of light source, uneven illumination intensity, etc.) and noise signals without data preprocessing.
Benefited from the reported framework, the research team firstly applied FPM to a self-developed whole slide imaging (WSI) platform, and realized full-color imaging with 4.7mm diameter FOV at a highest resolution of 336nm. This FPM-WSI instance demonstrates automatic high throughput imaging with low cost, and will offer a turnkey solution to transform the high-quality WSI platform into one that can be made broadly available and utilizable.
Experts in this field suppose that the reported method is expected to break the bottleneck that has long been constraining the development of FPM since its invention in 2013, making FPM more broadly accepted and utilized in the field of biomedical research and clinical applications.
Full-color FPM reconstructions for a human colorectal carcinoma section.（Image by XIOPM）
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