Quantitative phase imaging of living cells: application of the phase volume and area functions to the analysis of "nucleolar stress".

We applied coherent phase microscopy to develop a method of quantitative evaluation of functional state of eukaryotic cells using the coordinates of characteristic points (CP) in the functions of the phase volume W and area S. In a fragment of a single cell image (HCT116 human colon carcinoma cell line) with detectable nucleolus, the values of the phase thickness, area, and volume were calculated. These values dramatically changed within the initial minutes of cell exposure to the transcriptional inhibitor actinomycin D. The positions of CP in the graphs of S and W functions allowed for monitoring the time-dependent decrease of nucleolar contrast, a major optical hallmark of "nucleolar stress." Given that the area and volume functions reflect optical heterogeneity of the cell and are independent of its optical model, these functions can be applicable as general mathematical tools for the analysis of cell morphology and physiology.