Digital holography and cell studies

Digital holographic microscopy (DHM) is a novel high-resolution imaging technique that offers real-time imaging and quantitative measurements of physiological parameters. It has developed into a broad field, and one of many interesting applications is to study cells without staining or labeling them and without affecting them in any way. Digital holography makes it possible to easily measure cell properties that previously have been very difficult to study in living cells, such as cell thickness, volume, and cell refractive index (Marquet et al., 2005; Rappaz et al. 2005; Molder et al., 2008; El-Schish et al., in press; Persson et al., in press). Living, dying or dead cells as well as fixed cells can be studied. The first DHM images showing living cells were published in 2003 and 2004 (You et al., 2003; Carl et al., 2004), making this field of research rather new. Two of the most interesting functions of DHM is 3-D imaging of objects and to make in-focus measurements over time. Digital holography has been used to study a wide range of cells, e.g. protozoa, bacteria and plant cells as well as several types of mammalian cells such as nerve cells and tumor cells (Emery et al., 2007; Kemper et al., 2006; Moon and Javidi 2007). It has also been applied for studies of cell proliferation, cell movement and cell morphology (Kemper et al., 2009; Yu et al., 2009). Movement in both 2-D and 3-D has been studied (Langehanenberg et al., 2009; Persson et al., in press). In addition, cell viability status can be determined using DHM (Kemper et al., 2006; Kemmler et al., 2007). Interestingly, it is possible to study both single cells and entire populations simultaneously, allowing for very detailed studies. In this chapter we will compare DHM with previously used techniques and discuss the benefits and drawbacks of digital holography cell measurements. We will also present cell studies made possible by DHM.