Epi-mode tomographic quantitative phase imaging in thick scattering samples.

Quantitative phase imaging (QPI) is an important tool in biomedicine that allows for the microscopic investigation of live cells and other thin, transparent samples. Importantly, this technology yields access to the cellular and sub-cellular structure and activity at nanometer scales without labels or dyes. Despite this unparalleled ability, QPI's restriction to relatively thin samples severely hinders its versatility and overall utility in biomedicine. Here we overcome this significant limitation of QPI to enable the same rich level of quantitative detail in thick scattering samples. We achieve this by first illuminating the sample in an epi-mode configuration and using multiple scattering within the sample-a hindrance to conventional transmission imaging used in QPI-as a source of transmissive illumination from within. Second, we quantify phase via deconvolution by modeling the transfer function of the system based on the ensemble average angular distribution of light illuminating the sample at the focal plane. This technique packages the quantitative, real-time sub-cellular imaging capabilities of QPI into a flexible configuration, opening the door for truly non-invasive, label-free, tomographic quantitative phase imaging of unaltered thick, scattering specimens. Images of controlled scattering phantoms, blood in collection bags, cerebral organoids and freshly excised whole mouse brains are presented to validate the approach.