Quantitative phase imaging : a study from 2D to 3D

Abstract

In this thesis, quantitative phase imaging (QPI) techniques including 2D and 3D versions are investigated and presented. With QPI, biophysical and biochemical information of transparent biological micro-specimens can be measured and quantified. 2D quantitative phase maps of cell samples on the one hand can retrieve morphological shapes, and on the other hand can be converted to dry mass values, which are important bio-markers for cell growth studies. By adapting QPI system into an image cytometer, termed Quantitative phase cytometer (QPC), a large population of ~ 10⁴ HeLa cells were characterized with single-cell level morphology information and dry mass histogram. Next, in order to gain more accurate information such as nuclear shape, nuclear dry mass, and nuclear-to-cytoplasm volume ratio, 3D tomographic versions of QPI, i.e., tomographic phase microscopy (TPM), was introduced, which extended the QPI technique from 2D to 3D in imaging capability. To augment the throughput of TPM system, a digital micro-mirror device (DMD) was used to provide the angle scanning illumination, which significantly boosts the angle scanning speed to the magnitude of kHz. However, this angle scanning method suffers from the diffraction noise caused by the binary grating pattern, which significantly deteriorates the imaging quality. To solve this problem, a novel dynamic spatial filtering method was proposed to perfectly eliminate the diffraction noise for DMD based high-speed angle-scanning TPM systems. In summary, the QPI techniques in 2D and 3D modalities provide a promising quantitative tool for label-free characterization of biological samples.