THz Imaging Based on Water-Concentration Contrast

Terahertz medical imaging has emerged as a promising new field because of its non-ionizing photon energy and its acute sensitivity to water concentration. To better understand the primary contrast mechanism in THz imaging of tissues, the reflectivity of varying water concentrations was measured. Using a pulsed THz reflective imaging system, a 0.3 mm thin paper sample with varying water concentrations was probed and from the measured data a noise equivalent delta water concentration (NEAWC) of 0.054% was derived. The system is based on a photoconductive pulsed source and time-gated waveguide-mounted Schottky diode receiver. It operates at a center frequency of 500 GHz with 125 GHz of noise-equivalent bandwidth and at a standoff of 4 cm, the imaging system achieved a spot size of 2.2 mm. The high water sensitivity of this system was exploited to image burned porcine (pig) skin models in reflection using differences in water content of burned and unburned skin as the contrast mechanism. The obtained images of the porcine skin burns are a step towards the ability to quantify burn injuries using THz radiation.