Observing malaria in a new light; Fourier ptychography microscopy for volumetric imaging

Plasmodiumm spp., are the protozoan parasites responsible for malaria, and they convert the toxic heme into hemozoin as a protective mechanism.

The hemozoin crystals exhibit birefringence due to the varying refractive indices within their lattice structure, rendering them visible under cross-polarised light.

FPM is a relatively new advanced imaging technique which uses Fourier optics along with computational imaging to create high-resolution large field-of-view (FOV) images.

Ptychography is a computational imaging technique which captures multiple diffraction patterns of a sample from varying illumination angles and positions.

Fourier ptychography sequentially illuminates the sample from different LEDs within the inserted array, and then computationally merges this data into a single image that appears to have passed through a 'synthetic'; lens, whose effective size can extend across the entire cone of diffracted light to offer a much higher resolution.

In polarisation Fourier ptychography (PFP) the phase delay and optical axis is extracted depending on the crystal orientation, phase wrapping and sample thickness. There is potential, using different wavelengths to uncouple these effects.

By analysing these effects volumetric imaging can be achieved through structured illumination microscopy (SIM) or confocal microscopy.

There is a call for more analysis on the development of hemozoin crystals in malaria studies, therefore, analysing the effect of different wavelengths on these variables will provide invaluable information.

In addition, the point spread function of the system will be measured, to allow imaging/objective lens aberration correction and volumetric imaging.

Currently there are many phase and amplitude matching algorithms published, incorporating different strategies for image reconstruction, which will need to be adapted to improve resolution of birefringent images of malaria samples.