  Transmission optical coherence tomography (OCT) enables analysis of
biological specimens in vitro through detection of forward scattered light. Up
to now, transmission OCT was considered as a technique that cannot directly
retrieve quantitative phase and is thus a qualitative method. In this paper, we
present qtOCT, a novel quantitative transmission optical coherence tomography
method. Unlike existing approaches, qtOCT allows for a direct, easy, fast and
rigorous retrieval of 2D integrated phase information from transmission
full-field swept-source OCT measurements. Our method is based on coherence
gating and allows user-defined temporal measurement range selection, making it
potentially suitable for analyzing multiple-scattering samples. We demonstrate
high consistency between qtOCT and digital holographic microscopy phase images.
This approach enhances transmission OCT capabilities, positioning it as a
viable alternative to quantitative phase imaging techniques.
