On the use of multilook Fourier ptychographic microscopy for observing cells and tissues

Abstract

Fourier Ptychographic Microscopy (FPM) probes biological samples from multiple directions and provides amplitude and quantitative phase-contrast imaging in label-free modality with large space-bandwidth product. FPM is suitable to analyse tissues in hospitals and analysis labs by unskilled users. However, whenever any setup misalignment occurs, the actual illumination vector does not match the nominal one, which provokes an incorrect stitching of the low-resolution Fourier spectra and generates severe phase artefacts in the FPM reconstruction, thus preventing convergence to the sample complex amplitude. Such inconsistency between the nominal and the actual illumination vectors can be also induced by the presence of liquid films or drops on the sample plane, or light scattering. Here, we show the Multi-Look FPM method, which eliminates the unwanted artefacts and obtains correct quantitative phase-contrast images in labelfree mode over a 3.3 mm2 FoV with a 0.5 μm resolution. Our results add robustness and resiliency to FPM apparatus and will allow non-expert users exploiting FPM setups without calibration processes, becoming more accessible and available by unskilled personnel in diagnostic labs and hospitals. We demonstrate the effectiveness of the Multi-Look FPM method in the case of neural tissue slides, cell layers, and marine microalgae with complex inner structures.