As discussed previously in this book, terahertz (THz) electromagnetic waves, with their unique advantageous features, have been utilized to study biological phenomena. ey have also been applied to the eld of medicine, especially for testing THz technology as a future imaging modality. However, there are some drawbacks of THz waves with respect to their application to medical imaging. One of them is that it is dicult to obtain specic characteristic signals from biological tissues, cells, and macromolecules because the resonant characteristics are smeared out because of the inhomogeneous broadening of macromolecules and the large absorption by water molecules, which are abundant in living cells (Son 2009). e eect of water can be removed by lyophilizing cells and tissues (Png et al. 2008, Globus et al. 2012, Sim et al. 2013). e freezing technique, as described in Chapter 17, is also benecial to the enhancement of THz wave penetration into biological samples. Oh et al. developed another measurement depth enhancement technique in the imaging of biological samples with water by utilizing chemical gels, which have a lower absorption of THz waves than water and a refractive index that is at in the THz frequency range (Oh et al. 2013).