Measuring living systems is the ultimate challenge for biomedical research, as we do not want the act of taking the measurement to affect the system. Taking the measurement quickly has been a priority hitherto, but now that acquisition speeds are faster, we need to consider other aspects in more detail. Some key variables when measuring human skin in vivo include the contact pressure made with the THz probe and the duration of contact. In this talk I will present work by my group on THz spatial light modulators and other devices exploiting the total internal reflection geometry (TIR) which were developed to facilitate speeding up THz image acquisition and polarization control. I will explain how the TIR geometry of the THz modulator enhances sensitivity, and that this sensitivity can be useful for thin film material characterization. I will also present some of our recent results on applying THz imaging to characterize human skin in vivo as well as improving the contrast in excised wax embedded slices.