Accurate evaluation of size and refractive index for spherical objects in quantitative phase imaging

TL;DR

This paper introduces a new quantitative phase imaging fitting algorithm that accurately measures the size and refractive index of spherical objects by incorporating light-scattering effects, validated through simulations and experiments.

Contribution

The authors develop a novel QPI fitting method using Mie theory and a corrected Rytov approach to reliably decouple size and RI, improving over traditional geometrical methods.

Findings

The algorithm accurately uncouples size and RI in simulated data.

Experimental validation on various objects demonstrates robustness.

Provides practical guidelines for biological applications.

Abstract

Measuring the average refractive index (RI) of spherical objects, such as suspended cells, in quantitative phase imaging (QPI) requires a decoupling of RI and size from the QPI data. This has been commonly achieved by determining the object's radius with geometrical approaches, neglecting light-scattering. Here, we present a novel QPI fitting algorithm that reliably uncouples the RI using Mie theory and a semi-analytical, corrected Rytov approach. We assess the range of validity of this algorithm in silico and experimentally investigate various objects (oil and protein droplets, microgel beads, cells) and noise conditions. In addition, we provide important practical cues for future studies in cell biology.