Method for determining differentiation level of pluripotent stem cells

A method comprising the steps of:

• i) measuring flatness of at least one cultured pluripotent stem cell to determine whether the cultured pluripotent stem cell or a cultured pluripotent stem cell population is differentiated by applying a Student's t-test to compare the flatness of the cultured pluripotent stem cell or the cultured pluripotent stem cell population with those of undifferentiated pluripotent stem cells and differentiated cells, and
• ii) identifying and removing at least one cultured pluripotent stem cell that is determined to be differentiated,
• wherein the flatness of the cultured pluripotent stem cell or the cultured pluripotent stem cell population is measured from at least one tomographic image of a three-dimensional image of the cultured pluripotent stem cell or the cultured pluripotent stem cell population,
• wherein the measured flatness is flatness of a surface of the cultured pluripotent stem cell roughly parallel to a bottom surface of the cultured pluripotent stem cell attached to a culture vessel or flatness of a surface of the cultured pluripotent stem cell population roughly parallel to a bottom surface of the cultured pluripotent stem cell population attached to a culture vessel, and
• wherein the measured flatness of a differentiated cell or a differentiated cell population is statistically different from the measured flatness of an undifferentiated pluripotent stem cell or an undifferentiated pluripotent stem cell population.