Quantitative phase microscopy and synthetic aperture tomography of live cells

For more than a decade MIT's George R. Harrison Spectroscopy Laboratory has been developing quantitative phase microscopy (QPM) for biological study. Measurements of a point field were made in the mid 90s, then extended to the full 2D field, and recently, to 3D by using tomography. In the first part of this thesis improvements in the techniques of Fourier Phase Microscopy (FPM) and Hilbert Phase Microscopy (HPM) and their applications to characterize cells and tissues are reported. Tomographic phase microscopy (TPM) provides quantitative information and highly detailed structural information about a live cell, but in its current form it can only examine one cell at a time. Many biological applications including statistical analysis of a large collection of cells such as flow cytometry need a tomography technique that can measure many cells at a time. For the second part of this thesis we have developed a new tomography technique that can measure many cells continuously. In this study we demonstrate the new technique by translating a live cell across a focused beam. This beam is composed of many angular plane waves, and by applying a so-called synthetic aperture algorithm we retrieve individual wave components of the focused beam. We demonstrate for the first time that we can retrieve the field of the focused beam and synthesize any arbitrary angular plane wave. We then construct a 3D map of the variations of the refractive index in a live cell from a series of these synthesized angular plane waves. This new technique is the first step needed to analyze cells flowing through a beam to provide a high-throughput 3D refractive index tomograms that can be used as a new kind of statistical optical assay of living cells.