Autofocusing and edge detection schemes in cell volume measurements with quantitative phase microscopy

We have proposed and demonstrated a very sensitive volume measurement scheme for a live cell with a quantitative phase microscopy (QPM) utilizing auto-focusing and numerical edge detection schemes. An auto-focusing technique with two different focus measures is applied to find the focus dependent errors in our live cell volume measurement system. The volume of a polystyrene bead sample with 3 mum diameter has been measured for the validity test of our proposed method. We have shown that a small displacement of an object from its focusing position can cause a large volume error. A numerical edge detection technique is also used to accurately resolve the boundary between a cell and its suspension medium. We have applied this method to effectively suppress errors by the surrounding medium of a single red blood cell (RBC).