Fourier ptychographic microscopy aided with transport of intensity equation for robust full phase spectrum reconstruction

TL;DR

This paper introduces a hybrid Fourier ptychographic microscopy method combined with the transport of intensity equation to achieve robust, full-spectrum phase reconstruction with improved accuracy and noise robustness, especially for thick biological samples.

Contribution

It presents a novel hybrid approach integrating FPM with TIE, requiring only a single defocused image to recover low-frequency phase information and enhance phase reconstruction fidelity.

Findings

Enhanced phase reconstruction accuracy across spatial frequencies.

Ability to recover phase beyond the 0-2π range in thick samples.

Validated effectiveness on biological samples and test targets.

Abstract

Fourier ptychographic microscopy (FPM) is a pivotal computational imaging technique that achieves phase and amplitude reconstruction with high resolution and wide field of view, using low numerical aperture objectives and LED array illumination. Despite its unique strengths, FPM remains fundamentally limited in retrieving low spatial frequency phase information due to the absence of phase encoding in all brightfield illumination angles. To overcome this, we present a novel hybrid approach that combines FPM with the transport of intensity equation (TIE), enabling accurate, full-spectrum phase retrieval without compromising system simplicity. Our method extends standard FPM acquisitions with a single additional on-axis defocused image, from which low-frequency phase components are reconstructed via TIE method, employing large defocus distance to suppress low-frequency artifacts and enhance robustness to intensity noise. To additionally compensate for defocus-induced magnification variations caused by spherical wavefront illumination, we employ an affine transform-based correction scheme upon image registration. Notably, by restoring the missing low-frequency content, our hybrid method appears capable of recovering phase values beyond the conventional 0-2{\pi} range - an area where conventional FPM techniques often struggle when dealing with optically thick samples. We validated our method using a quantitative phase test target for benchmarking accuracy and biological cheek cells, mouse neurons, and mouse brain tissue slice samples to demonstrate applicability for in vitro bioimaging. Experimental results confirm substantial improvements in phase reconstruction fidelity across spatial frequencies, establishing this hybrid FPM+TIE framework as a practical and high-performance solution for quantitative phase imaging in biomedical and optical metrology applications.