Multi-Aperture Fourier Ptychographic Microscopy: development of a high-speed gigapixel coherent computational microscope

[摘要] Medical research and clinical diagnostics require imaging of large sample areas with sub-cellular resolution. Conventional imaging techniques can provide either high-resolution or wide field-of-view (FoV) but not both. This compromise is conventionally defeated by using a high NA objective with a small FoV and then mechanically scan the sample in order to acquire separate images of its different regions. By stitching these images together, a larger effective FoV is then obtained. This procedure, however, requires precise and expensive scanning stages and prolongs the acquisition time, thus rendering the observation of fast processes/phenomena impossible. A novel imaging configuration termed Multi-Aperture Fourier Ptychographic Microscopy (MA-FPM) is proposed here based on Fourier ptychography (FP), a technique to achieve wide-FoV and high-resolution using time-sequential synthesis of a high-NA coherent illumination. MA-FPM configuration utilises an array of objective lenses coupled with detectors to increase the bandwidth of the object spatial-frequencies captured in a single snapshot. This provides high-speed data-acquisition with wide FoV, high-resolution, long working distance and extended depth-of-field.In this work, a new reconstruction method based on Fresnel diffraction forward model was developed to extend FP reconstruction to the proposed MA-FPM technique. MA-FPM was validated experimentally by synthesis of a 3x3 lens array system from a translating objective-detector system. Additionally, a calibration procedure was also developed to register dissimilar images from multiple cameras and successfully implemented on the experimental data. A nine-fold improvement in captured data-bandwidth was demonstrated. Another experimental configuration was proposed using the Scheimpflug condition to correct for the aberrations present in the off-axis imaging systems. An experimental setup was built for this new configuration using 3D printed parts to minimise the cost. The design of this setup is discussed along with robustness analysis of the low-cost detectors used in this setup. A reconstruction model for the Scheimpflug configuration FP was developed and applied to the experimental data. Preliminary experimental results were found to be in agreement with this reconstruction model. Some artefacts were observed in these results due to the calibration errors in the experiment. These can be corrected by using the self-calibration algorithm proposed in the literature, which is left as a future work. Extensions to this work can include implementing multiplexed illumination for further increasing the data acquisition speed and diffraction tomography for imaging thick samples.

[发布机构] University:University of Glasgow;Department:School of Physics and Astronomy

[关键词] Fourier ptychography, synthetic aperture, microscopy, phase imaging, camera array, high speed imaging, Scheimpflug.