  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.
