Holotomography (HT) uses laser interferometry to measure 3-D refractive index (RI) distribution. HT serves as a powerful tool for imaging small transparent objects, such as biological cells and tissues. HT is an optical analogous to X-ray computed tomography (CT); HT measured multiple 2-D holograms of a sample with various illumination angles, from which a 3-D RI distribution of the sample is reconstructed by inversely solving the wave equation. Unlike conventional fluorescence-based imaging techniques, HT provides label-free 3-D imaging capability. Without any fixation or labeling, 3-D images of live cells can be obtained with high spatial resolution (down to 110 nm). Furthermore, HT provides quantitative imaging capability: RI maps of a cell are precisely and quantitative measured, from which various cellular analysis can be followed. 

We present the principle and applications of HT in various fields, including cell biology, microbiology, and hematology. Also, we also present the recently developed multimodal system which simultaneously measures the 3-D RI tomogram and 3-D fluorescence image of a sample, and enables unprecedented correlative and quantitative bioimaging capability. 

Learning Objectives: 

1. To understand the working principle of holotomography 
2. To learn direct applications of holotomography in the field of biology and medicine