Three-dimensional refractive-index microscope for analyzing thalassemia

Hematological properties of erythrocytes are associated with various blood-related diseases. Clinically, physicians make a diagnosis mainly based on blood reports obtained using Complete Blood Count (CBC), which is a common tool to measure average values of fundamental indicators such as the volume, hemoglobin content and hemoglobin concentration of all erythrocytes analyzed. However, the information about individual erythrocytes, as well as morphological information, is unavailable for physicians. Common-path tomographic diffractive microscope (cTDM) is a novel three-dimensional (3-D) quantitative phase imaging technique that can acquire 3-D refractive index (RI) images of living cells. We employed cTDM to acquire 3-D RI images of erythrocytes obtained from normal volunteers and patients with mild thalassemia. Only about 0.5 μL of blood is sufficient for imaging with cTDM while CBC needs at least 1 mL. Additionally, we calculated the dry mass of each erythrocyte from phase images after experimentally estimating the specific refractive increment of hemoglobin using custom-made microfluidic channels. The diagnostic accuracy of various indices demonstrates that the total phase and the ratio of volume to surface area are the best parameters to distinguish between the normal and thalassemia erythrocytes.