Recent advances in terahertz technology for biomedical applications

Abstract

Terahertz instrumentation has improved significantly in recent years such that THz imaging systems have become more affordable and easier to use. THz systems can now be operated by non-THz experts greatly facilitating research into many potential applications. Due to the non-ionising nature of THz light and its high sensitivity to soft tissues, there is an increasing interest in biomedical applications including both in vivo and ex vivo studies. Additionally, research continues into understanding the origin of contrast and how to interpret terahertz biomedical images. This short review highlights some of the recent work in these areas and suggests some future research directions.

Keywords: Terahertz imaging; biological contrast; cancer imaging; terahertz modelling; terahertz spectroscopy.

Figure 1

Demonstrating the hysteresis effect due to slow freeze/thaw cycles in porcine tissue. (A) Optical images of the fresh porcine muscle and fat samples; (B) absorption coefficient vs refractive index for fresh, frozen and thawed porcine muscle samples. Adapted with permission from (6).

Figure 2

Instead of freezing tissue or removing water content, gelatin embedding presents an alternative way to preserve tissue for terahertz imaging studies. (A) Photograph of gelatin embedded porcine skin; (B) schematic cross-section of the THz measurement of a gelatin embedded sample. Adapted with permission from (12).

Figure 3

Diabetic foot measurement studies using THz. (A) Photograph of the measurement set-up. THz images plotting the calculated water volume for (B) a control and (C) a diabetic patient. (D) Calculated water volume for control and diabetic patients using data from the centre of the big toe. Adapted with permission from (22).

Figure 4

Corneal THz reflectivity maps for two rabbit subjects, with the central corneal thickness (CCT) measurement range in millimetres and corresponding Corneal Tissue Water Content (CTWC) given in percent, supplied from ultrasound measurements. Time increases, from left to right and top to bottom for each image series. The dotted circles overlaid on the top left cornea of each image denote the ultrasound probe location.

Figure 5

(A) Absorption coefficient, (B) refractive index and (C) visual image of a hypertrophic scar six months post-injury. The refractive index image continues to show significant differences between normal and scarred tissue, which may be indicative of some realignment of collagen fibres in the scarred tissue. Adapted with permission from (30).

Figure 6

(A) Histology image and high-resolution THz images at 1.5 THz for regions I (B) and II (C). The reflected THz amplitudes for the IDC regions are clearly higher than for the surrounding fatty and fibrous parts.

Figure 7

(A) Schematic of the TIR optical pumping THz modulator (B) TIR signal for different optical pumping powers. In (C) a schematic of a proposed compressed sensing imaging system based upon this approach is shown. (D,E) show the reflected THz intensity when either no optical light is incident upon the TIR interface, or when optical light is pumping three of the four quadrants as shown by the dotted lines and the inset legends (black: light off, red: light on), thereby demonstrating the potential for spatial modulation. Adapted from (53).