Exploring the impedance-matching effect in terahertz reflection imaging of skin tissue

Abstract

Terahertz (THz) electromagnetic waves, known for their unique response to water, offer promising opportunities for next-generation biomedical diagnostics and novel cancer therapy technologies. This study investigated the impedance-matching effect, which enhances the efficiency of THz wave delivery into tissues and compensates for the signal distortion induced by the refractive index mismatch between the target and the sample substrate. Three candidate biocompatible materials, water, glycerol, and petroleum jelly were applied to a skin phantom and compared using THz two-dimensional imaging and time-of-flight imaging methods. Finally, we successfully demonstrated impedance-matching effect on mouse skin tissues.

Fig. 1.

Scheme of reflection-mode THz imaging system. The THz imaging system was based on the fiber laser.

Fig. 2.

Imaging of water, glycerol and petroleum jelly drop on quartz window: (a) Photograph and (b) THz peak to peak images of air (A), water (W), glycerol (G), and petroleum jelly (P) (norm.: normalized amplitude).

Fig. 3.

THz waveforms of water, glycerol and petroleum jelly drop on quartz window of Fig. 2 (a.u.: arbitrary unit),

Fig. 4.

THz complex constants of commercial hydrogel patch (a) refractive indices and extinction coefficients and (b) absorption coefficients of commercial hydrogel patch.

Fig. 5.

Imaging of hydrogel patch on the quartz window (a) Photograph and (b) THz peak to peak images of air (A), water (W), glycerol (G), and petroleum jelly (P) (norm.: normalized amplitude).

Fig. 6.

THz TOF images of vertical short dot line of Fig. 5(a) Hydrogel patch without impedance-matching materials and applied glycerol, and (b) Hydrogel patch applied water and petroleum jelly. The dot line boxes indicate the location of samples (a.u.: arbitrary unit).

Fig. 7.

THz TOF images of horizontal long dot line of Fig. 4: (a) Hydrogel patch without and with water, and (b) Hydrogel patch applied glycerol and petroleum jelly (a.u.: arbitrary unit).

Fig. 8.

THz time-domain waveforms of the dotted lines of Fig. 7 (a.u.: arbitrary unit).

Fig. 9.

3-demension volumetric image of hydrogel patch on the quartz window of Fig. 5.

Fig. 10.

Imaging of animal skin on the quartz window: (a) Photograph and (b) THz peak to peak images of (A) air, (W) water, glycerol (G), and petroleum jelly (P) (norm.: normalized amplitude).